Publications by authors named "Giovanni Agati"

38 Publications

Application of a Combined Transmittance/Fluorescence Leaf Clip Sensor for the Nondestructive Determination of Nitrogen Status in White Cabbage Plants.

Sensors (Basel) 2021 Jan 12;21(2). Epub 2021 Jan 12.

Istituto di Fisica Applicata "Nello Carrara"-CNR, Via Madonna del Piano, 10-50019 Sesto Fiorentino (FI), Italy.

The correct fertilization of vegetable crops is commonly determined on the basis of soil and plant costly destructive analyses, demanding more sustainable non-invasive optical detection. Here, we tested the ability of the combined transmittance/fluorescence leaf clip Dualex device for determining the nitrogen (N) status of cabbage plants. Fully developed leaves from plants grown under different N rates of 0; 100; 200; 300 kg N ha in 2018 and 2019 were measured in the field by the Dualex sensor twice a year in July and October. The chlorophyll (Chl) and nitrogen (nitrogen balance index, NBI) indices and the flavonols (Flav) index of the sensor were positively and negatively correlated to leaf nitrogen, respectively. Merging the two-years data, the NBI versus leaf N correlation was less point dispersed in October than July (R = 0.76 and 0.64, respectively). NBI was also correlated to cabbage yield, better in July than October. Our results showed that the multiparametric Dualex device can be used as precision agriculture tool for the early prediction of plant N and cabbage yield with economic advantage for the growers and reduced environmental contamination due to nitrate leaching.
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http://dx.doi.org/10.3390/s21020482DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7827347PMC
January 2021

Are Flavonoids Effective Antioxidants in Plants? Twenty Years of Our Investigation.

Antioxidants (Basel) 2020 Nov 9;9(11). Epub 2020 Nov 9.

Institute for Sustainable Plant Protection, National Research Council of Italy (CNR), Via Madonna del Piano 10, I-50019, Sesto F.no, Florence, Italy.

Whether flavonoids play significant antioxidant roles in plants challenged by photooxidative stress of different origin has been largely debated over the last few decades. A critical review of the pertinent literature and our experimentation as well, based on a free-of-scale approach, support an important antioxidant function served by flavonoids in plants exposed to a wide range of environmental stressors, the significance of which increases with the severity of stress. On the other side, some questions need conclusive answers when the putative antioxidant functions of plant flavonoids are examined at the level of both the whole-cell and cellular organelles. This partly depends upon a conclusive, robust, and unbiased definition of "a plant antioxidant", which is still missing, and the need of considering the subcellular re-organization that occurs in plant cells in response to severe stress conditions. This likely makes our deterministic-based approach unsuitable to unveil the relevance of flavonoids as antioxidants in extremely complex biological systems, such as a plant cell exposed to an ever-changing stressful environment. This still poses open questions about how to measure the occurred antioxidant action of flavonoids. Our reasoning also evidences the need of contemporarily evaluating the changes in key primary and secondary components of the antioxidant defense network imposed by stress events of increasing severity to properly estimate the relevance of the antioxidant functions of flavonoids in an in planta situation. In turn, this calls for an in-depth analysis of the sub-cellular distribution of primary and secondary antioxidants to solve this still intricate matter.
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http://dx.doi.org/10.3390/antiox9111098DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7695271PMC
November 2020

Short-Term Pre-Harvest UV-B Supplement Enhances the Polyphenol Content and Antioxidant Capacity of Leaves during Storage.

Plants (Basel) 2020 Jun 25;9(6). Epub 2020 Jun 25.

University of Florence, Department of Agriculture, Food, Environment and Forestry (DAGRI), Section Woody Plants, CAP. 50019 Sesto Fiorentino (Florence), Italy.

(basil) leaves are rich in polyphenols, conferring them a high antioxidant activity. The application of UV-B can be used to maintain the post-harvest nutraceutical quality of basil leaves. We aimed to investigate the effects of pre-harvest UV-B application on polyphenolic and pigment contents, antioxidant capacity, and the visual quality of basil stored leaves. We also evaluated the applicability of the non-invasive Dualex for monitoring the accumulation of leaf epidermal phenolics (Flav Index). After exposing plants to white light (control) and to supplemental UV-B radiation for 4 d, the leaves were harvested and stored for 7d (T). The UV-B leaves showed both a higher phenolic content and antioxidant capacity than the controls at T. In addition, the correlations between the Flav Index and phenolic content demonstrated that Dualex can reliably assess the content of epidermal phenolics, thus confirming its promising utilization as a non-destructive method for monitoring the phytochemical quality of leaves. In conclusion, a pre-harvesting UV-B application may be a tool for enhancing the content of polyphenols and the antioxidant potential of basil stored leaves without detrimental effects on their visual quality. These results are important considering the nutraceutical value of this plant and its wide commercial distribution.
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http://dx.doi.org/10.3390/plants9060797DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7361986PMC
June 2020

Unveiling the shade nature of cyanic leaves: A view from the "blue absorbing side" of anthocyanins.

Plant Cell Environ 2021 Apr 14;44(4):1119-1129. Epub 2020 Jul 14.

Institute for Sustainable Plant Protection, National Research Council of Italy, Florence, Italy.

Anthocyanins have long been suggested as having great potential in offering photoprotection to plants facing high light irradiance. Nonetheless, their effective ability in protecting the photosynthetic apparatus from supernumerary photons has been questioned by some authors, based upon the inexact belief that anthocyanins almost exclusively absorb green photons, which are poorly absorbed by chlorophylls. Here we focus on the blue light absorbing features of anthocyanins, a neglected issue in anthocyanin research. Anthocyanins effectively absorb blue photons: the absorbance of blue relative to green photons increases from tri- to mono-hydroxy B-ring substituted structures, reaching up to 50% of green photons absorption. We offer a comprehensive picture of the molecular events activated by low blue-light availability, extending our previous analysis in purple and green basil, which we suggest to be responsible for the "shade syndrome" displayed by cyanic leaves. While purple leaves display overexpression of genes promoting chlorophyll biosynthesis and light harvesting, in green leaves it is the genes involved in the stability/repair of photosystems that are largely overexpressed. As a corollary, this adds further support to the view of an effective photoprotective role of anthocyanins. We discuss the profound morpho-anatomical adjustments imposed by the epidermal anthocyanin shield, which reflect adjustments in light harvesting capacity under imposed shade and make complex the analysis of the photosynthetic performance of cyanic versus acyanic leaves.
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http://dx.doi.org/10.1111/pce.13818DOI Listing
April 2021

Fluorescence-Sensor Mapping for the in Vineyard Non-Destructive Assessment of Crimson Seedless Table Grape Quality.

Sensors (Basel) 2020 Feb 12;20(4). Epub 2020 Feb 12.

Istituto di Fisica Applicata "Nello Carrara" IFAC, Consiglio Nazionale delle Ricerche, Via Madonna del Piano 10, 50019 Sesto Fiorentino, Italy.

Non-destructive tools for the in situ evaluation of vine fruit quality and vineyard management can improve the market value of table grape. We proposed a new approach based on a portable fluorescence sensor to map the ripening level of Crimson Seedless table grape in five different plots in the East, Central-North and South of the Macedonia Region of Greece. The sensor provided indices of ripening and color such as SFR and ANTH correlated to the chlorophyll and anthocyanin berry contents, respectively. The mean ANTH index was significantly different among all the plots examined due to the occurrence of different environmental conditions and/or asynchronous ripening processes. The indices presented moderate, poor in some cases, spatial variability, probably due to a significant vine-to-vine, intra-vine and intra-bunch variability. The cluster analysis was applied to the plot with the most evident spatial structure (at Kilkis). Krigged maps of the SFR, ANTH and yield were classified by k-means clustering in two-zones that differed significantly in their mean values. ANTH and SFR were inversely correlated over 64% of the plot. SFR appeared to be a potential useful proxy of yield since it was directly correlated to yield over 66% of the plot. The grape color (ANTH) was slightly higher over the low-yield zones with respect to the high-yield zones. Our study showed that the combination of anthocyanins and chlorophyll indices detected in the field on Crimson Seedless table grape by a portable fluorescence sensor can help in defining the best harvest time and the best areas for harvesting.
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http://dx.doi.org/10.3390/s20040983DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7070766PMC
February 2020

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Foods 2019 Jun 27;8(7). Epub 2019 Jun 27.

Department of Process Technology, Nofima - Norwegian Institute of Food, Fisheries and Aquaculture Research, N-4068 Stavanger, Norway.

There is a large potential in Europe for valorization in the vegetable food supply chain. For example, there is occasionally overproduction of tomatoes for fresh consumption, and a fraction of the production is unsuited for fresh consumption sale (unacceptable color, shape, maturity, lesions, etc.). In countries where the facilities and infrastructure for tomato processing is lacking, these tomatoes are normally destroyed, used as landfilling or animal feed, and represent an economic loss for producers and negative environmental impact. Likewise, there is also a potential in the tomato processing industry to valorize side streams and reduce waste. The present paper provides an overview of tomato production in Europe and the strategies employed for processing and valorization of tomato side streams and waste fractions. Special emphasis is put on the four tomato-producing countries Norway, Belgium, Poland, and Turkey. These countries are very different regards for example their climatic preconditions for tomato production and volumes produced, and represent the extremes among European tomato producing countries. Postharvest treatments and applications for optimized harvest time and improved storage for premium raw material quality are discussed, as well as novel, sustainable processing technologies for minimum waste and side stream valorization. Preservation and enrichment of lycopene, the primary health promoting agent and sales argument, is reviewed in detail. The European volume of tomato postharvest wastage is estimated at >3 million metric tons per year. Together, the optimization of harvesting time and preprocessing storage conditions and sustainable food processing technologies, coupled with stabilization and valorization of processing by-products and side streams, can significantly contribute to the valorization of this underutilized biomass.
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http://dx.doi.org/10.3390/foods8070229DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6678325PMC
June 2019

Comparison of lycopene changes between open-field processing and fresh market tomatoes during ripening and post-harvest storage by using a non-destructive reflectance sensor.

J Sci Food Agric 2019 Apr 22;99(6):2763-2774. Epub 2018 Dec 22.

Istituto di Fisica Applicata 'Nello Carrara' - CNR, Sesto Fiorentino, Italy.

Background: Accumulation and stability of tomato lycopene markedly depends on the cultivar, plant growing and storage conditions. To estimate lycopene in open-field cultivated processing and fresh market tomatoes, we used a calibrated spectral reflectance portable sensor.

Results: Lycopene accumulation in fruits attached to the plant, starting from the Green ripening stage, followed a sigmoidal function. It was faster and reached higher levels in processing (cv. Calista) than fresh market (cv. Volna) tomatoes (90 and 62 mg kg fresh weight, respectively). During storage at 12, 20 and 25 °C, Red tomatoes retained about 90% of harvest lycopene for three weeks. Pink tomatoes increased lycopene during the first week of storage, but never reached the lycopene values of Red tomatoes ripened on the vine. Storability at 12 °C retaining the highest quality in red tomatoes was limited to 14 and 7 days for Calista and Volna cultivars, respectively.

Conclusion: Significant differences in lycopene accumulation and stability between processing and fresh market tomatoes were established by examining with time the very same fruits by a non-destructive optical tool. It can be useful in agronomical and post-harvest physiological studies and can be of interest for producers oriented to the niche nutraceutical market. © 2018 Society of Chemical Industry.
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http://dx.doi.org/10.1002/jsfa.9484DOI Listing
April 2019

Multiple Consequences Induced by Epidermally-Located Anthocyanins in Young, Mature and Senescent Leaves of .

Front Plant Sci 2018 2;9:917. Epub 2018 Jul 2.

Department of Agriculture, Food and Environment, University of Pisa, Pisa, Italy.

Anthocyanic morphs are generally less efficient in terms of carbon gain, but, in turn, are more photoprotected than anthocyanin-less ones. To date, mature leaves of different morphs or leaves at different developmental stages within the same species have generally been compared, whereas there is a lack of knowledge regarding different stages of development of red . green leaves. Leaves (1-, 7-, and 13-week-old) of red- (RLP) and green-leafed (GLP) in terms of photosynthetic rate, carbon metabolism and photoprotective mechanisms were compared to test whether anthocyanin-equipped leaves perform better than anthocyanin-less leaves and whether photoprotection is the primary role of epidermally-located anthocyanins, using for the first time a recently-developed parameter of chlorophyll fluorescence (qPd). GLP leaves had a higher photosynthetic rate in 1- and 7-week-old leaves, but RLP leaves performed better at an early stage of senescence and had a longer leaf lifespan. Anthocyanins contributed to leaf photoprotection throughout the leaf development, but were tightly coordinated with carotenoids. Besides photoprotecting, we propose that epidermal anthocyanins may be principally synthetized to maintain an efficient carbon-sink strength in young and senescent leaves, thus extending the RLP leaf lifespan.
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http://dx.doi.org/10.3389/fpls.2018.00917DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6036500PMC
July 2018

Management Zone Delineation for Winegrape Selective Harvesting Based on Fluorescence-Sensor Mapping of Grape Skin Anthocyanins.

J Agric Food Chem 2018 Jun 4;66(23):5778-5789. Epub 2018 Jun 4.

Ecologie Systématique Evolution , Univ. Paris-Sud, CNRS, AgroParisTech, Université Paris-Saclay , Bât. 362, 91400 Orsay , France.

We analyzed the potential of non-destructive optical sensing of grape skin anthocyanins for selective harvesting in precision viticulture. We measured anthocyanins by a hand-held fluorescence optical sensor on a 7 ha Sangiovese vineyard plot in central Italy. Optical indices obtained by the sensor were calibrated for the transformation in units of anthocyanins per berry mass, i.e., milligrams per gram of berry fresh weight. A full protocol for optimal data filtration, interpolation, and homogeneous zone delineation based on a very large number of optical measurements is proposed. Both the single signal-based fluorescence index (ANTH) and the two signal ratio-based index (ANTH) can be used for Sangiovese grapes. Significant separations of grape-quality batches were obtained by several methods of data classification and zone delineations. Basic statistical criteria were as efficient as the K-means clustering. The best separations were obtained for three classes of grape skin anthocyanin.
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http://dx.doi.org/10.1021/acs.jafc.8b01326DOI Listing
June 2018

Prediction Models for Assessing Lycopene in Open-Field Cultivated Tomatoes by Means of a Portable Reflectance Sensor: Cultivar and Growing-Season Effects.

J Agric Food Chem 2018 May 27;66(18):4748-4757. Epub 2018 Apr 27.

Istituto di Fisica Applicata "Nello Carrara"-CNR , Via Madonna del Piano, 10 - 50019 Sesto Fiorentino (FI) , Italy.

Reflectance spectroscopy represents a useful tool for the nondestructive assessment of tomato lycopene, even in the field. For this reason, a compact, low-cost, light emitting diode-based sensor has been developed to measure reflectance in the 400-750 nm spectral range. It was calibrated against wet chemistry and evaluated by partial least squares (PLS) regression analyses. The lycopene prediction models were defined for two open-field cultivated red-tomato varieties: the processing oblong tomatoes of the cv. Calista (average weight: 76 g) and the fresh-consumption round tomatoes of the cv. Volna (average weight: 130 g), over a period of two consecutive years. The lycopene prediction models were dependent on both cultivar and season. The lycopene root mean square error of prediction produced by the 2014 single-cultivar calibrations validated on the 2015 samples was large (33 mg kg) in the Calista tomatoes and acceptable (9.5 mg kg) in the Volna tomatoes. A more general bicultivar and biyear model could still explain almost 80% of the predicted lycopene variance, with a relative error in red tomatoes of less than 20%. In 2016, the in-field applications of the multiseasonal prediction models, built with the 2014 and 2015 data, showed significant ( P < 0.001) differences in the average lycopene estimated in the crop on two sampling dates that were 20 days apart: on August 19 and September 7, 2016, the lycopene was 98.9 ± 9.3 and 92.2 ± 10.8 mg kg FW for cv. Calista and 54.6 ± 13.2 and 60.8 ± 6.8 mg kg FW for cv. Volna. The sensor was also able to monitor the temporal evolution of lycopene accumulation on the very same fruits attached to the plants. These results indicated that a simple, compact reflectance device and PLS analysis could provide adequately precise and robust (through-seasons) models for the nondestructive assessment of lycopene in whole tomatoes. This technique could guarantee tomatoes with the highest nutraceutical value from the production, during storage and distribution, and finally to consumers.
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http://dx.doi.org/10.1021/acs.jafc.8b01570DOI Listing
May 2018

Prediction models for assessing anthocyanins in grape berries by fluorescence sensors: Dependence on cultivar, site and growing season.

Food Chem 2018 Apr 7;244:213-223. Epub 2017 Oct 7.

Istituto di Fisica Applicata "Nello Carrara" IFAC, Consiglio Nazionale delle Ricerche, Via Madonna del Piano 10, 50019 Sesto Fiorentino, Firenze, Italy.

Fluorescence sensors are useful tools for the non-destructive assessment of grape berry anthocyanins. The Multiplex (Mx) sensor here studied provides two anthocyanin indices: ANTH = log(1/Chl-fluorescence_R) and ANTH = log(Chl-fluorescence_R/Chl-fluorescence_G), based on the chlorophyll (Chl) fluorescence excited with red (R) and green (G) light. These indices were calibrated against wet chemistry. The dependence of anthocyanin prediction models on cultivar, season and site was studied on four cultivars in two Italian regions during three consecutive years. The 2010 global model (all cultivars at both growing sites) gave relative prediction errors on anthocyanin content less than 14.1% (ANTH) and 19.0% (ANTH). The ANTH was independent of season, maintaining a relative error of about 20% in both 2011 and 2012. In field applications of the calibrated Mx, it showed its ability to detect inter-plot and inter-season differences on both growing sites.
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http://dx.doi.org/10.1016/j.foodchem.2017.10.021DOI Listing
April 2018

Nondestructive Optical Sensing of Flavonols and Chlorophyll in White Head Cabbage (Brassica oleracea L. var. capitata subvar. alba) Grown under Different Nitrogen Regimens.

J Agric Food Chem 2016 Jan 28;64(1):85-94. Epub 2015 Dec 28.

Research Institute of Horticulture, Konstytucji 3 Maja 1/3, 96-100 Skierniewice, Poland.

A multiparametric optical sensor was used to nondestructively estimate phytochemical compounds in white cabbage leaves directly in the field. An experimental site of 1980 white cabbages (Brassica oleracea L. var. capitata subvar. alba), under different nitrogen (N) treatments, was mapped by measuring leaf transmittance and chlorophyll fluorescence screening in one leaf/cabbage head. The provided indices of flavonols (FLAV) and chlorophyll (CHL) displayed the opposite response to applied N rates, decreasing and increasing, respectively. The combined nitrogen balance index (NBI = CHL/FLAV) calculated was able to discriminate all of the plots under four N regimens (0, 100, 200, and 400 kg/ha) and was correlated with the leaf N content determined destructively. CHL and FLAV were properly calibrated against chlorophyll (R(2) = 0.945) and flavonol (R(2) = 0.932) leaf contents, respectively, by using a homographic fit function. The proposed optical sensing of cabbage crops can be used to estimate the N status of plants and perform precision fertilization to maintain acceptable crop yield levels and, additionally, to rapidly detect health-promoting flavonol antioxidants in Brassica plants.
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http://dx.doi.org/10.1021/acs.jafc.5b04962DOI Listing
January 2016

Esculetin and esculin (esculetin 6-O-glucoside) occur as inclusions and are differentially distributed in the vacuole of palisade cells in Fraxinus ornus leaves: a fluorescence microscopy analysis.

J Photochem Photobiol B 2014 Nov 28;140:28-35. Epub 2014 Jun 28.

Istituto di Fisica Applicata 'Carrara' (IFAC), Consiglio Nazionale delle Ricerche, Via Madonna del Piano 10, I-50019, Sesto. F. no, Firenze, Italy. Electronic address:

The location of individual coumarins in leaves of Fraxinus ornus acclimated at full solar irradiance was estimated using their specific UV- and fluorescence spectral features. Using a combination of UV-induced fluorescence and blue light-induced fluorescence of tissues stained with diphenylborinic acid 2-amino-ethylester, in wide field or confocal laser scanning microscopy, we were able to visualize the distribution of esculetin and esculetin 6-O-glucoside (esculin) in palisade cells. Coumarins are not uniformly distributed in the cell vacuole, but accumulate mostly in the adaxial portion of palisade cells. Our study indeed shows, for the first time, that coumarins in palisade cells accumulate as vacuolar inclusions, as previously reported in the pertinent literature only for anthocyanins. Furthermore, esculetin and esculin have a different vacuolar distribution: esculetin largely predominates in the first 15 μm from the adaxial epidermis. This leads to hypothesize for esculetin and esculin different transport mechanisms from the endoplasmic reticulum to the vacuole as well as potentially different roles in photoprotection. Our study open to new experiments aimed at exploring the mechanisms that deliver coumarins to the vacuole using different fluorescence signatures of coumarin aglycones and coumarin glycosides.
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http://dx.doi.org/10.1016/j.jphotobiol.2014.06.012DOI Listing
November 2014

Isoprene production in transgenic tobacco alters isoprenoid, non-structural carbohydrate and phenylpropanoid metabolism, and protects photosynthesis from drought stress.

Plant Cell Environ 2014 Aug 22;37(8):1950-64. Epub 2014 May 22.

Institute for Plant Protection, Department of Biology, Agriculture and Food Sciences, The National Research Council of Italy (CNR), I-50019, Sesto Fiorentino (Florence), Italy.

Isoprene strengthens thylakoid membranes and scavenges stress-induced oxidative species. The idea that isoprene production might also influence isoprenoid and phenylpropanoid pathways under stress conditions was tested. We used transgenic tobacco to compare physiological and biochemical traits of isoprene-emitting (IE) and non-emitting (NE) plants exposed to severe drought and subsequent re-watering. Photosynthesis was less affected by drought in IE than in NE plants, and higher rates were also observed in IE than in NE plants recovering from drought. Isoprene emission was stimulated by mild drought. Under severe drought, isoprene emission declined, and levels of non-volatile isoprenoids, specifically de-epoxidated xanthophylls and abscisic acid (ABA), were higher in IE than in NE plants. Soluble sugars and phenylpropanoids were also higher in IE plants. After re-watering, IE plants maintained higher levels of metabolites, but isoprene emission was again higher than in unstressed plants. We suggest that isoprene production in transgenic tobacco triggered different responses, depending upon drought severity. Under drought, the observed trade-off between isoprene and non-volatile isoprenoids suggests that in IE plants isoprene acts as a short-term protectant, whereas non-volatile isoprenoids protect against severe, long-term damage. After drought, it is suggested that the capacity to emit isoprene might up-regulate production of non-volatile isoprenoids and phenylpropanoids, which may further protect IE leaves.
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http://dx.doi.org/10.1111/pce.12350DOI Listing
August 2014

Potential of a multiparametric optical sensor for determining in situ the maturity components of red and white Vitis vinifera wine grapes.

J Agric Food Chem 2013 Dec 5;61(50):12211-8. Epub 2013 Dec 5.

Istituto di Fisica Applicata 'N. Carrara'-CNR , Via Madonna del Piano 10, 50019 Sesto Fiorentino (FI), Italy.

A nondestructive fluorescence-based technique for evaluating Vitis vinifera L. grape maturity using a portable sensor (Multiplex) is presented. It provides indices of anthocyanins and chlorophyll in Cabernet Sauvignon, Merlot, and Sangiovese red grapes and of flavonols and chlorophyll in Vermentino white grapes. The good exponential relationship between the anthocyanin index and the actual anthocyanin content determined by wet chemistry was used to estimate grape anthocyanins from in field sensor data during ripening. Marked differences were found in the kinetics and the amount of anthocyanins between cultivars and between seasons. A sensor-driven mapping of the anthocyanin content in the grapes, expressed as g·kg(-1) fresh weight, was performed on a 7-ha vineyard planted with Sangiovese. In the Vermentino, the flavonol index was favorably correlated to the actual content of berry skin flavonols determined by means of HPLC analysis of skin extracts. It was used to make a nondestructive estimate of the evolution in the flavonol concentration in grape berry samplings. The chlorophyll index was inversely correlated in a linear manner to the total soluble solids (°Brix): it could, therefore, be used as a new index of technological maturity. The fluorescence sensor (Multiplex) possesses a high potential for representing an important innovative tool for controlling grape maturity in precision viticulture.
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http://dx.doi.org/10.1021/jf405099nDOI Listing
December 2013

Fluorescence approach for measuring anthocyanins and derived pigments in red wine.

J Agric Food Chem 2013 Oct 9;61(42):10156-62. Epub 2013 Oct 9.

Institute of Applied Physics, National Research Council, Sesto Fiorentino (Florence), Italy.

A novel fluorescence approach to monitor the evolution of anthocyanins and derivatives in red wine was developed. Some red table wines and Port wine with different vintage years were first tested with the aim to determine the ideal fluorescent conditions. The fluorescence contribution of both monomeric and polymeric anthocyanins was studied by comparing their emission spectra. By measuring the F700/F560 ratio on different wine samples and applying an inverted exponential function, it was possible to estimate the monomeric/polymeric anthocyanin absorbance ratio that is proportional to the relative content of the two classes of compounds. The methodology was further developed by using pure compounds representative of monomeric anthocyanins and anthocyanin-pyruvic acid adducts, namely, by using malvidin-3-O-glucoside and vitisin A. A fluorescence excitation ratio (FER350/550) was considered for estimating the absorbance ratio between vitisin A and malvidin-3-O-glucoside. Overall, this work aims to use fluorescence to monitor the evolution of anthocyanin derivatives and to distinguish them from their anthocyanin precursors, thereby allowing the evolution of anthocyanin pigments during wine aging to be monitored, but it also may be useful to determine age markers or even geographical markers.
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http://dx.doi.org/10.1021/jf402398aDOI Listing
October 2013

Characterisation of the polyphenol content in the kiwifruit (Actinidia deliciosa) exocarp for the calibration of a fruit-sorting optical sensor.

Phytochem Anal 2013 Sep-Oct;24(5):460-6. Epub 2013 May 28.

Department of Pharmaceutical Sciences, University of Florence, Via Ugo Schiff 6, 50019, Sesto Fiorentino, Firenze, Italy.

Introduction: Kiwifruit contains high amounts of anti-oxidants beneficial to health. Its quality is influenced by ripening time, genotype, cultivation techniques, climate and storage conditions after harvest.

Objective: The aim of the present study was to characterise the phenolic content by HPLC methods and to evaluate the performance of a portable optical sensor (Multiplex 3), for in vivo non-destructive phenolic compound assessment in kiwifruits.

Methods: Kiwifruits peel extracts were characterised by reverse-phase (RP) HPLC with diode-array detector (DAD) and electrospray ionisation (ESI) with MS using the Zorbax SB-Aq. column from Agilent. The fluorimetric sensor method is based on the screening of fruit chlorophyll fluorescence excitation and allows the UV absorbance of intact fruit skin to be measured. The flavonol index, FLAV, was calculated as log(FRF(R)/FRF(UV)), where FRF(R) and FRF(UV) are the chlorophyll fluorescence excited with red and UV light.

Results: Hydroxycinnamic acids, procyanidins, and quercetin glycosides were the main polyphenol classes detected by HPLC-DAD-ESI/MS in the kiwifruit skin. A good linear regression (R²  = 0.88) was found between the fluorimetric sensor FLAV index and flavonol chromatographic analysis of the fruits. The FLAV index was able to detect the higher content of flavonols in sun-exposed fruits with respect to mid-shaded and shaded ones in accordance with the destructive analysis.

Conclusion: The fluorimetric sensor represents a rapid and non-invasive tool to: (i) monitor the flavonol accumulation in kiwifruit and to assess its quality concerning the healthy anti-oxidant properties; (ii) evaluate the effect of environmental and agronomical factors related to the fruit quality; and (iii) select fruits with the largest flavonol content, and consequently less susceptible to pathogen attack, in order to improve their storage durability.
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http://dx.doi.org/10.1002/pca.2443DOI Listing
March 2014

Functional roles of flavonoids in photoprotection: new evidence, lessons from the past.

Plant Physiol Biochem 2013 Nov 28;72:35-45. Epub 2013 Mar 28.

Istituto di Fisica Applicata 'Carrara', IFAC, Consiglio Nazionale delle Ricerche, Via Madonna del Piano 10, I-50019 Sesto Fiorentino, Firenze, Italy.

We discuss on the relative significance of different functional roles potentially served by flavonoids in photoprotection, with special emphasis to their ability to scavenge reactive oxygen species (ROS) and control the development of individual organs and whole plant. We propose a model in which chloroplast-located flavonoids scavenge H2O2 and singlet oxygen generated under excess light-stress, thus avoiding programmed cell death. We also draw a picture in which vacuolar flavonoids in conjunction with peroxidases and ascorbic acid constitute a secondary antioxidant system aimed at detoxifying H2O2, which may diffuse out of the chloroplast at considerable rates and enter the vacuole following excess light stress-induced depletion of ascorbate peroxidase. We hypothesize for flavonols key roles as developmental regulators in early and current-day land-plants, based on their ability to modulate auxin movement and auxin catabolism. We show that antioxidant flavonoids display the greatest capacity to regulate key steps of cell growth and differentiation in eukaryotes. These regulatory functions of flavonoids, which are shared by plants and animals, are fully accomplished in the nM concentration range, as likely occurred in early land plants. We therefore conclude that functions of flavonoids as antioxidants and/or developmental regulators flavonoids are of great value in photoprotection. We also suggest that UV-B screening was just one of the multiple functions served by flavonoids when early land-plants faced an abrupt increase in sunlight irradiance.
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http://dx.doi.org/10.1016/j.plaphy.2013.03.014DOI Listing
November 2013

Flavonoids as antioxidants in plants: location and functional significance.

Plant Sci 2012 Nov 11;196:67-76. Epub 2012 Aug 11.

Consiglio Nazionale delle Ricerche, Istituto di Fisica Applicata 'Carrara', Via Madonna del Piano 10, I-50019 Sesto F. No, Firenze, Italy.

Stress-responsive dihydroxy B-ring-substituted flavonoids have great potential to inhibit the generation of reactive oxygen species (ROS) and reduce the levels of ROS once they are formed, i.e., to perform antioxidant functions. These flavonoids are located within or in the proximity of centers of ROS generation in severely stressed plants. Efficient mechanisms have been recently identified for the transport of flavonoids from the endoplasmic reticulum, the site of their biosynthesis, to different cellular compartments. The mechanism underlying flavonoid-mediated ROS reduction in plants is still unclear. 'Antioxidant' flavonoids are found in the chloroplast, which suggests a role as scavengers of singlet oxygen and stabilizers of the chloroplast outer envelope membrane. Dihydroxy B-ring substituted flavonoids are present in the nucleus of mesophyll cells and may inhibit ROS-generation making complexes with Fe and Cu ions. The genes that govern the biosynthesis of antioxidant flavonoids are present in liverworts and mosses and are mostly up-regulated as a consequence of severe stress. This suggests that the antioxidant flavonoid metabolism is a robust trait of terrestrial plants. Vacuolar dihydroxy B-ring flavonoids have been reported to serve as co-substrates for vacuolar peroxidases to reduce H(2)O(2) escape from the chloroplast, following the depletion of ascorbate peroxidase activity. Antioxidant flavonoids may effectively control key steps of cell growth and differentiation, thus acting regulating the development of the whole plant and individual organs.
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http://dx.doi.org/10.1016/j.plantsci.2012.07.014DOI Listing
November 2012

BVOC emission from Populus × canadensis saplings in response to acute UV-A radiation.

Physiol Plant 2013 May 1;148(1):51-61. Epub 2012 Oct 1.

Institute of AgroEnvironmental and Forest Biology, National Research Council, 00015, Monterotondo Scalo, RM, Italy.

Hybrid poplar (Populus × canadensis) saplings were subjected to acute ultraviolet-A (UV-A) irradiation (30 W m(-2) , ambient treatment, 60, 90 and 120 W m(-2) of UV-A irradiance) to determine the effects on photosynthesis and biogenic volatile organic compound (BVOC) emissions in two different short-term experiments (i.e. sequential increase in UV-A irradiance and UV-A intensity-response relationships). Both intensity-response experiments showed that the UV-A ambient treatment did not affect photosynthesis and BVOC emissions. Whereas exposition at 60, 90 and 120 W m(-2) of UV-A (first experiment), increasingly inhibited photosynthesis. This increasing inhibition was also detected by decreasing trends of both photochemical reflectance index (PRI) and fluorescence yield. Isoprene emission resulted to be very sensitive to increasing UV-A irradiances. Methanol was also very sensitive to high UV-A radiation, suggesting the occurrence of strong damages of cellular structures. The second experiment, which was performed both in the middle of July and repeated towards the end of the summer, showed a temporal variations in the UV-A intensity-response relationships. In fact, there were no longer significant differences in photosynthesis, PRI and isoprene emission in response to high UV-A radiation toward the end of the summer season. The adaxial flavonoid level increased significantly over the period monitored, resulting 85% higher toward the end of the summer than during the middle of the summer. This dramatic increase in the adaxial flavonoids may have played a protective role against UV-A radiation by shielding leaves. Our findings add to the understanding of physiological processes involved in plant response to UV radiation.
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http://dx.doi.org/10.1111/j.1399-3054.2012.01687.xDOI Listing
May 2013

Non-destructive evaluation of ripening and quality traits in apples using a multiparametric fluorescence sensor.

J Sci Food Agric 2012 Jul 9;92(9):1855-64. Epub 2012 Jan 9.

"Faculdade de Agronomia Eliseu Maciel", Universidade Federal de Pelotas, Campus Universitário s/n, Caixa Posta n° 354-Pelotas, RS, Brazil.

Background: The detection of pigments and colourless flavonoids in apples can provide a useful indication of fruit quality. Optical methods are preferable because they are fast and non-destructive. In this study, a fluorescence-based portable sensor was used in order to non-invasively determine the content of chlorophylls, anthocyanins and flavonols in Fuji, Granny Smith and Golden Delicious apple cultivars. The aim was to define new non-destructive optical indices of apple quality.

Results: The anthocyanin index (ANTH) in Fuji was higher in the sunny (i.e. sun-exposed) side of the fruit compared to the shady side. For all cultivars, the flavonol index (FLAV) was higher in the sunny side compared with the shady side. The chlorophyll index (CHL) for the shady sides of Granny Smith and Golden Delicious was significantly higher than for the sunny sides. Fine linear regressions were found between the ANTH, FLAV and CHL indices and the actual anthocyanin, flavonol and chlorophyll concentrations, respectively, which were determined destructively on the apple peel extracts. A negative correlation was found between the apple sugar content and the chlorophyll fluorescence in the far-red spectral band.

Conclusion: Our results indicate that a single multiparametric fluorescence-based sensor can provide valuable non-destructive markers of ripening and quality in apples.
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http://dx.doi.org/10.1002/jsfa.5552DOI Listing
July 2012

A retrieval algorithm to evaluate the Photosystem I and Photosystem II spectral contributions to leaf chlorophyll fluorescence at physiological temperatures.

Photosynth Res 2011 Sep 25;108(2-3):225-39. Epub 2011 Aug 25.

Istituto di Fisica Applicata Nello Carrara, CNR, Via Madonna del Piano 10, 50019, Sesto Fiorentino, Firenze, Italy.

A new computational procedure to resolve the contribution of Photosystem I (PSI) and Photosystem II (PSII) to the leaf chlorophyll fluorescence emission spectra at room temperature has been developed. It is based on the Principal Component Analysis (PCA) of the leaf fluorescence emission spectra measured during the OI photochemical phase of fluorescence induction kinetics. During this phase, we can assume that only two spectral components are present, one of which is constant (PSI) and the other variable in intensity (PSII). Application of the PCA method to the measured fluorescence emission spectra of Ficus benjamina L. evidences that the temporal variation in the spectra can be ascribed to a single spectral component (the first principal component extracted by PCA), which can be considered to be a good approximation of the PSII fluorescence emission spectrum. The PSI fluorescence emission spectrum was deduced by difference between measured spectra and the first principal component. A single-band spectrum for the PSI fluorescence emission, peaked at about 735 nm, and a 2-band spectrum with maxima at 685 and 740 nm for the PSII were obtained. A linear combination of only these two spectral shapes produced a good fit for any measured emission spectrum of the leaf under investigation and can be used to obtain the fluorescence emission contributions of photosystems under different conditions. With the use of our approach, the dynamics of energy distribution between the two photosystems, such as state transition, can be monitored in vivo, directly at physiological temperatures. Separation of the PSI and PSII emission components can improve the understanding of the fluorescence signal changes induced by environmental factors or stress conditions on plants.
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http://dx.doi.org/10.1007/s11120-011-9678-5DOI Listing
September 2011

The biosynthesis of flavonoids is enhanced similarly by UV radiation and root zone salinity in L. vulgare leaves.

J Plant Physiol 2011 Feb 20;168(3):204-12. Epub 2010 Sep 20.

Istituto di Fisica Applicata Carrara, IFAC, Consiglio Nazionale delle Ricerche, Via Madonna del Piano 10, I-50019 Sesto. F.no, Firenze, Italy.

Flavonoids have recently been suggested to have the potential to serve as antioxidants other than effective UV attenuators in photoprotection. Here, we tested the hypothesis that flavonoids accumulate in response to "excess light" in the presence or in the absence of UV radiation. In a UV exclusion experiment, we grew Ligustrum vulgare plants outdoors under 30% or 100% sunlight irradiance, by cutting-off the whole UV waveband. These plants were also exposed to UV irradiance or supplied with 125 mM NaCl at the root zone. Leaves of plants under 100% sunlight irradiance suffered from excess light, which was exacerbated greatly by root zone salinity stress. Salinity stress repressed the activities of antioxidant enzymes, particularly in full sunlight, and led to severe leaf oxidative damage. Dihydroxy B-ring-substituted flavonoids, namely quercetin 3-O- and luteolin 7-O-glycosides, accumulated steeply in response to sunlight irradiance in the absence of UV radiation. UV radiation and root zone NaCl increased, to a similar degree, the concentration of these flavonoids, which have a great potential to scavenge various forms of reactive oxygen. Treatment-induced changes in leaf phenylpropanoid concentration affected antioxidant activities to a greater extent than the UV-screening capacities of leaf extracts. Early responses to an abrupt increase in sunlight irradiance included a steep increase in the concentrations of quercetin derivatives and cyanidin 3-O-glucoside, with the latter negligibly absorbing in the UV-spectral region. In contrast, effective UV attenuators, such as hydroxycinnamates and monohydroxy B-ring flavonoids, were unresponsive to the light treatments. Overall, these findings lead to the hypothesis that flavonoids may have an important antioxidant function in photoprotection. This hypothesis is further corroborated by the large distribution of quercetin and luteolin derivatives in the vacuoles of mesophyll, not only in the corresponding compartments of epidermal cells, but also in full sunlight-treated leaves in the absence of UV radiation. Future experiments aimed at evaluating the relative contribution of flavonoids within the complex antioxidant defense systems operating in the leaf are needed to help conclusively address the relevance of their antioxidant functions in photoprotection.
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http://dx.doi.org/10.1016/j.jplph.2010.07.016DOI Listing
February 2011

Multiple functional roles of flavonoids in photoprotection.

New Phytol 2010 Jun;186(4):786-793

Istituto per la Protezione delle Piante, Consiglio Nazionale delle Ricerche, Via Madonna del Piano 10, I-50019, Sesto F.no, Firenze, Italy.

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http://dx.doi.org/10.1111/j.1469-8137.2010.03269.xDOI Listing
June 2010

Mesophyll distribution of 'antioxidant' flavonoid glycosides in Ligustrum vulgare leaves under contrasting sunlight irradiance.

Ann Bot 2009 Oct 25;104(5):853-61. Epub 2009 Jul 25.

Istituto di Fisica Applicata Carrara, IFAC, Consiglio Nazionale delle Ricerche, I-50019, Sesto Fiorentino, Firenze, Italy.

Background And Aims: Flavonoids have the potential to serve as antioxidants in addition to their function of UV screening in photoprotective mechanisms. However, flavonoids have long been reported to accumulate mostly in epidermal cells and surface organs in response to high sunlight. Therefore, how leaf flavonoids actually carry out their antioxidant functions is still a matter of debate. Here, the distribution of flavonoids with effective antioxidant properties, i.e. the orthodihydroxy B-ring-substituted quercetin and luteolin glycosides, was investigated in the mesophyll of Ligustrum vulgare leaves acclimated to contrasting sunlight irradiance.

Methods: In the first experiment, plants were grown at 20 % (shade) or 100% (sun) natural sunlight. Plants were exposed to 100 % sunlight irradiance in the presence or absence of UV wavelengths, in a second experiment. Fluorescence microspectroscopy and multispectral fluorescence microimaging were used in both cross sections and intact leaf pieces to visualize orthodihydroxy B-ring-substituted flavonoids at inter- and intracellular levels. Identification and quantification of individual hydroxycinnamates and flavonoid glycosides were performed via HPLC-DAD.

Key Results: Quercetin and luteolin derivatives accumulated to a great extent in both the epidermal and mesophyll cells in response to high sunlight. Tissue fluorescence signatures and leaf flavonoid concentrations were strongly related. Monohydroxyflavone glycosides, namely luteolin 4'-O-glucoside and two apigenin 7-O-glycosides were unresponsive to changes in sunlight irradiance. Quercetin and luteolin derivatives accumulated in the vacuoles of mesophyll cells in leaves growing under 100 % natural sunlight in the absence of UV wavelengths.

Conclusions: The above findings lead to the hypothesis that flavonoids play a key role in countering light-induced oxidative stress, and not only in avoiding the penetration of short solar wavelengths in the leaf.
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http://dx.doi.org/10.1093/aob/mcp177DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2749533PMC
October 2009

Antioxidant defences and oxidative damage in salt-treated olive plants under contrasting sunlight irradiance.

Tree Physiol 2009 Sep 16;29(9):1187-98. Epub 2009 Jul 16.

Departamento de Agronomia, Universidad de Córdoba, Edificio Celestino Mutis, Campus Universitario de Rabanales, 14071 Córdoba, Spain.

The interactive effects of root-zone salinity and sunlight on leaf biochemistry, with special emphasis on antioxidant defences, were analysed in Olea europaea L. cv. Allora, during the summer period. Plants were grown outside under 15% (shade plants) or 100% sunlight (sun plants) and supplied with 0 or 125 mM NaCl. The following measurements were performed: (1) the contribution of ions and soluble carbohydrates to osmotic potentials; (2) the photosystem II (PSII) photochemistry and the photosynthetic pigment concentration; (3) the concentration and the tissue-specific distribution of leaf flavonoids; (4) the activity of antioxidant enzymes; and (5) the leaf oxidative damage. The concentrations of Na(+) and Cl(-) were significantly greater in sun than in shade leaves, as also observed for the concentration of the 'antioxidant' sugar-alcohol mannitol. The de-epoxidation state of violaxanthin-cycle pigments increased in response to salinity stress in sun leaves. This finding agrees with a greater maximal PSII photochemistry (F(v)/F(m)) at midday, detected in salt-treated than in control plants, growing in full sunshine. By contrast, salt-treated plants in the shade suffered from midday depression in F(v)/F(m) to a greater degree than that observed in control plants. The high concentration of violaxanthin-cycle pigments in sun leaves suggests that zeaxanthin may protect the chloroplast from photo-oxidative damage, rather than dissipating excess excitation energy via non-photochemical quenching mechanisms. Dihydroxy B-ring-substituted flavonoid glycosides accumulate greatly in the mesophyll, not only in the epidermal cells, in response to high sunlight. The activity of antioxidant enzymes varied little because of sunlight irradiance, but declined sharply in response to high salinity in shade leaves. Interestingly, control and particularly salt-treated plants in the shade underwent greater oxidative damage than their sunny counterparts. These findings, which conform to the evolution of O. europaea in sunny environments, suggest that under partial shading, the antioxidant defence system may be ineffective to counter salt-induced oxidative damage.
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http://dx.doi.org/10.1093/treephys/tpp047DOI Listing
September 2009

Chlorophyll fluorescence imaging for the noninvasive assessment of anthocyanins in whole grape (Vitis vinifera L.) bunches.

Photochem Photobiol 2008 Nov-Dec;84(6):1431-4. Epub 2008 Aug 27.

Istituto di Fisica Applicata Nello Carrara, Consiglio Nazionale delle Ricerche, Florence, Italy.

The distribution of anthocyanins in grape (Vitis vinifera L.) bunches from the Sangiovese cultivar was measured nondestructively by chlorophyll fluorescence imaging using two excitation light bands at 550 and 650 nm in sequence. The pixel intensity in the derived logarithm of the fluorescence excitation ratio image was directly related, by an exponential function (r2 = 0.93), to the anthocyanin concentration of berry extracts. The method will be useful for the assessment of the heterogeneity of anthocyanin accumulation in berries that is known to depend on physiologic and climatic factors. It can also represent a new, rapid and noninvasive technique for the assessment of grape ripening and the appropriate time of harvest.
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http://dx.doi.org/10.1111/j.1751-1097.2008.00424.xDOI Listing
February 2009

Optically-assessed preformed flavonoids and susceptibility of grapevine to Plasmopara viticola under different light regimes.

Funct Plant Biol 2008 Feb;35(1):77-84

Dipartimento di Scienze Agronomiche e Gestione del Territorio Agro-forestale, Università degli Studi di Firenze, Piazzale delle Cascine 18, 50144 Firenze, Italy.

The role of flavonoids in the response of plants to Plasmopara viticola, the phytopathogen agent of downy mildew, was studied in the Vitis vinifera L. cultivar Sangiovese. Grapevines in the vineyard were exposed to two light regimes, 100% and 35% of full sunlight in order to induce differences in total leaf polyphenolic content. Epidermal leaf phenolic compounds were assessed optically, using the Dualex chlorophyll fluorescence-based portable leaf-clip. Dualex data were calibrated by means of HPLC analysis of extracts from the same measured leaves. Good correlations were obtained with total flavonoid contents, which consist mainly of quercetin 3-O-glucuronide. From the Dualex non-destructive measurements, we showed that full-sun exposed leaves contained 75% more flavonoids than shaded leaves. Inoculation of leaves with P. viticola sporangia resulted in a significantly lower infected leaf area in sun-lit leaves compared with shaded ones, as seen from subsequent analysis of the downy mildew severity. These results indicated an inverse relationship between preformed flavonoids and the susceptibility of grapevines to downy mildew. The rapid optical method for the non-destructive assessment of flavonoids presented here could be useful for large scale screening and predicting V. vinifera susceptibility to P. viticola.
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http://dx.doi.org/10.1071/FP07178DOI Listing
February 2008

Therapeutic effect of turquoise versus blue light with equal irradiance in preterm infants with jaundice.

Acta Paediatr 2007 Jun;96(6):837-41

Department of Pediatrics, University Hospital of Aalborg, Aalborg, Denmark.

Aim: To compare the efficiency of turquoise light with that of TL52 blue in treatment of preterm infants with jaundice at the same level of body irradiance.

Methods: Infants with gestational age 28-37 weeks and non-haemolytic hyperbilirubinemia were treated for 24 h with either turquoise light (OSRAM L18W/860 fluorescent lamps) or blue light (Philips TL20W/52 fluorescent lamps). The concentrations of serum total bilirubin and bilirubin isomers were measured by the Vitros routine method and by HPLC, respectively.

Results: The decrease in serum concentrations of total bilirubin, total bilirubin isomers and the toxic Z,Z-bilirubin was greatest for infants treated with turquoise light. Further, the increase in Z,E-bilirubin was smaller and there was a trend towards a higher rise in E,Z-bilirubin.

Conclusions: Turquoise light has a greater bilirubin reducing effect than TL52 blue light with equal irradiance, expressed both by serum total bilirubin, total bilirubin isomers and Z,Z-bilirubin, i.e. the turquoise spectral range is more efficient than the blue. This is in accordance with deeper penetration into the skin, lower production of the Z,E-bilirubin and greater production of E,Z-bilirubin and lumirubin, in infants under turquoise light. This suggests, given equal irradiances, that light in the turquoise spectral range is preferable to the TL52 blue in treatment of newborn jaundiced infants.
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http://dx.doi.org/10.1111/j.1651-2227.2007.00261.xDOI Listing
June 2007

Chloroplast-located flavonoids can scavenge singlet oxygen.

New Phytol 2007 ;174(1):77-89

Istituto per la Valorizzazione del Legno e delle Specie Arboree, IVALSA, Consiglio Nazionale delle Ricerche, Via Madonna del Piano 10, I-50019, Sesto F.no, Firenze, Italy.

* The hypothesis was tested that flavonoids may scavenge singlet oxygen ((1)O(2)) in mesophyll cells of Phillyrea latifolia exposed to excess-light stress. * In cross-sections taken from leaves developed at 10% (shade) or 100% (sun) solar irradiance, we evaluated the excess photosynthetically active radiation (PAR)-induced accumulation of (1)O(2) in mesophyll cells by imaging the fluorescence quenching of the specific (1)O(2) probe N-[2-(diethylamino)ethyl]-N-[(2,5-dihydro-2,2,5,5-tetramethyl-1H-pyrrol-3-yl)methyl]-5-(dimethylamino)-1-naphthalenesulfonamide (DanePy). The intracellular location of flavonoids was also analyzed using three-dimensional deconvolution microscopy. * Photo-induced quenching of DanePy fluorescence was markedly greater in the mesophyll of shade leaves than in that of sun leaves, the former showing a negligible accumulation of mesophyll flavonoids. The photo-induced generation of (1)O(2) was inversely related to the content of flavonoids in the mesophyll cells of sun leaves. Flavonoids were located in the chloroplasts, and were likely associated with the chloroplast envelope. * Here we provide relevant evidence for the potential scavenger activity of chloroplast-located flavonoids against (1)O(2) and new insights into the photo-protective role of flavonoids in higher plants.
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http://dx.doi.org/10.1111/j.1469-8137.2007.01986.xDOI Listing
June 2007