Publications by authors named "Jaume Flexas"

117 Publications

Adjustments in photosynthesis and leaf water relations are related to changes in cell wall composition in Hordeum vulgare and Triticum aestivum subjected to water deficit stress.

Plant Sci 2021 Oct 5;311:111015. Epub 2021 Aug 5.

Research Group on Plant Biology Under Mediterranean Conditions, Departament de Biologia, Universitat de Les Illes Balears (UIB) - Agro-Environmental and Water Economics Institute (INAGEA), Carretera de Valldemossa Km 7.5, 07122, Palma, Illes Balears, Spain; King Abdulaziz University, Jeddah, Saudi Arabia. Electronic address:

In the current climate change scenario, understanding crops' physiological performance under water shortage is crucial to overcome drought periods. Although the implication of leaf water relations maintaining leaf turgor and stomatal functioning under water deprivation has been suggested, the relationships between photosynthesis and osmotic and elastic adjustments remain misunderstood. Similarly, only few studies in dicotyledonous analysed how changes in cell wall composition affected photosynthesis and leaf water relations under drought. To induce modifications in photosynthesis, leaf water relations and cell wall composition, Hordeum vulgare and Triticum aestivum were subjected to different water regimes: control (CL, full irrigation), moderate and severe water deficit stress (Mod WS and Sev WS, respectively). Water shortage decreased photosynthesis mainly due to stomatal conductance (g) declines, being accompanied by reduced osmotic potential at full turgor (π) and increased bulk modulus of elasticity (ε). Whereas both species enhanced pectins when intensifying water deprivation, species-dependent adjustments occurred for cellulose and hemicelluloses. From these results, we showed that π and ε influenced photosynthesis, particularly, g. Furthermore, the (Cellulose+Hemicelluloses)/Pectins ratio determined ε and mesophyll conductance (g) in grasses, presenting the lowest pectins content within angiosperms. Thus, we highlight the relevance of cell wall composition regulating grasses physiology during drought acclimation.
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http://dx.doi.org/10.1016/j.plantsci.2021.111015DOI Listing
October 2021

Cell wall thickness and composition are related to photosynthesis in Antarctic mosses.

Physiol Plant 2021 Aug 25. Epub 2021 Aug 25.

Departament de Biologia, Research Group on Plant Biology under Mediterranean Conditions, Universitat de les Illes Balears (UIB), INAGEA, Palma, Illes Balears, Spain.

Cell wall thickness (T ) has been proposed as an important anatomical trait that could determine photosynthesis through land plants' phylogeny, bryophytes being the plant group presenting the thickest walls and the lowest photosynthetic rates. Also, it has recently been suggested that cell wall composition may have the potential to influence both thickness and mesophyll conductance (g ), representing a novel trait that could ultimately affect photosynthesis. However, only a few studies in spermatophytes have demonstrated this issue. In order to explore the role of cell wall composition in determining both T and g in mosses, we tested six species grown under field conditions in Antarctica. We performed gas exchange and chlorophyll fluorescence measurements, an anatomical characterization, and a quantitative analysis of cell wall main composition (i.e., cellulose, hemicelluloses and pectins) in these six species. We found the photosynthetic rates to vary between the species, and they also presented differences in anatomical characteristics and in cell wall composition. Whilst g correlated negatively with T and pectins content, a positive relationship between T and pectins emerged, suggesting that pectins could contribute to determine cell wall porosity. Although our results do not allow us to provide conclusive statements, we suggest for the first time that cell wall composition-with pectins playing a key role-could strongly influence T and g in Antarctic mosses, ultimately defining photosynthesis.
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http://dx.doi.org/10.1111/ppl.13533DOI Listing
August 2021

Dynamic changes in cell wall composition of mature sunflower leaves under distinct water regimes affect photosynthesis.

J Exp Bot 2021 Aug 11. Epub 2021 Aug 11.

Research Group on Plant Biology under Mediterranean Conditions, Departament de Biologia, Universitat de les Illes Balears (UIB), INAGEA. Carretera de Valldemossa Km 7.5, 07122 Palma de Mallorca, Illes Balears, Spain.

Based on a previous work, exposure to limited water availability induced changes in cell wall composition of mature Helianthus annuus L. leaves that affected mesophyll conductance to CO2 diffusion (gm). However, it is unclear on which timescale these cell wall composition changes occur. Here, we tested H. annuus subjected to control (i.e., water availability), different levels of short-term water deficit stress (ST), long-term water deficit stress (LT) and long-term water deficit stress followed by gradual recoveries addressed at different timescales (LT-Rec) to evaluate the dynamics of modifications in cell wall main composition (cellulose, hemicelluloses, pectins and lignins) affecting photosynthesis. During gradual ST treatments, pectins enhancements were associated with gm declines. However, during LT-Rec, pectins content decreased significantly after only 5 h, while hemicelluloses and lignins amounts changed after 24 h, all of them being uncoupled from gm. Surprisingly, lignins increased by around 200% as compared to control and were related to stomatal conductance to gas diffusion (gs) during LT-Rec. Although we suspect that the accuracy of the protocols to determine cell wall composition should be re-evaluated, we demonstrate for the first time that a highly dynamic cell wall composition turnover differently affects photosynthesis in plants subjected to distinct water regimes.
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http://dx.doi.org/10.1093/jxb/erab372DOI Listing
August 2021

Leaf anatomical characteristics are less important than leaf biochemical properties in determining photosynthesis responses to nitrogen top-dressing.

J Exp Bot 2021 07;72(15):5709-5720

Research Group on Plant Biology under Mediterranean Conditions, Universitat de les Illes Balears/Instituto de Investigaciones Agroambientales y de Economía del Agua (INAGEA), Carretera de Valldemossa Km 7.5, Palma de Mallorca, Illes Balears, Spain.

The photosynthetic capacity of leaves is dramatically influenced by nitrogen (N) availability in the soil, as CO2 concentration in chloroplasts and photosynthetic biochemical capacity are related to leaf N content. The relationship between mesophyll conductance (gm) and leaf N content was expected to be shaped by leaf anatomical traits. However, the increased gm in mature leaves achieved by N top-dressing is unlikely to be caused by changes in leaf anatomy. Here, we assessed the impacts of N supply on leaf anatomical, biochemical, and photosynthetic features, specifically, the dynamic responses of leaf anatomy, biochemistry, and photosynthesis to N top-dressing in tobacco. Plant performance was substantially affected by soil N status. In comparison with the leaves of plants subjected to low N treatment, leaves of plants with high N treatment photosynthesized significantly more, due to higher CO2 diffusion conductance and photosynthetic biochemical capacity. The high gm in high N-treated leaves apparently related to modifications in the leaf anatomy; however, the rapid response of gm to N top-dressing cannot be fully explained by leaf anatomical modifications.
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http://dx.doi.org/10.1093/jxb/erab230DOI Listing
July 2021

Differences in biochemical, gas exchange and hydraulic response to water stress in desiccation tolerant and sensitive fronds of the fern Anemia caffrorum.

New Phytol 2021 08 5;231(4):1415-1430. Epub 2021 Jun 5.

Department of Molecular and Cell Biology, University of Cape Town, Private Bag X3, Rondebosch, 7701, South Africa.

Desiccation tolerant plants can survive extreme water loss in their vegetative tissues. The fern Anemia caffrorum produces desiccation tolerant (DT) fronds in the dry season and desiccation sensitive (DS) fronds in the wet season, providing a unique opportunity to explore the physiological mechanisms associated with desiccation tolerance. Anemia caffrorum plants with either DT or DS fronds were acclimated in growth chambers. Photosynthesis, frond structure and anatomy, water relations and minimum conductance to water vapour were measured under well-watered conditions. Photosynthesis, hydraulics, frond pigments, antioxidants and abscisic acid contents were monitored under water deficit. A comparison between DT and DS fronds under well-watered conditions showed that the former presented higher leaf mass per area, minimum conductance, tissue elasticity and lower CO assimilation. Water deficit resulted in a similar induction of abscisic acid in both frond types, but DT fronds maintained higher stomatal conductance and upregulated more prominently lipophilic antioxidants. The seasonal alternation in production of DT and DS fronds in A. caffrorum represents a mechanism by which carbon gain can be maximized during the rainy season, and a greater investment in protective mechanisms occurs during the hot dry season, enabling the exploitation of episodic water availability.
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http://dx.doi.org/10.1111/nph.17445DOI Listing
August 2021

Cell wall thickness and composition are involved in photosynthetic limitation.

J Exp Bot 2021 05;72(11):3971-3986

School of Biological Sciences, University of Tasmania, Hobart, TAS, Australia.

The key role of cell walls in setting mesophyll conductance to CO2 (gm) and, consequently, photosynthesis is reviewed. First, the theoretical properties of cell walls that can affect gm are presented. Then, we focus on cell wall thickness (Tcw) reviewing empirical evidence showing that Tcw varies strongly among species and phylogenetic groups in a way that correlates with gm and photosynthesis; that is, the thicker the mesophyll cell walls, the lower the gm and photosynthesis. Potential interplays of gm, Tcw, dehydration tolerance, and hydraulic properties of leaves are also discussed. Dynamic variations of Tcw in response to the environment and their implications in the regulation of photosynthesis are discussed, and recent evidence suggesting an influence of cell wall composition on gm is presented. We then propose a hypothetical mechanism for the influence of cell walls on photosynthesis, combining the effects of thickness and composition, particularly pectins. Finally, we discuss the prospects for using biotechnology for enhancing photosynthesis by altering cell wall-related genes.
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http://dx.doi.org/10.1093/jxb/erab144DOI Listing
May 2021

Acclimation of mesophyll conductance and anatomy to light during leaf aging in Arabidopsis thaliana.

Physiol Plant 2021 Aug 30;172(4):1894-1907. Epub 2021 Mar 30.

Research Group in Plant Biology under Mediterranean Conditions, Universitat de les Illes Balears, Palma, Spain.

Mesophyll conductance (g ), a key limitation to photosynthesis, is strongly driven by leaf anatomy, which is in turn influenced by environmental growth conditions and ontogeny. However, studies examining the combined environment × age effect on both leaf anatomy and photosynthesis are scarce, and none have been carried out in short-lived plants. Here, we studied the variation of photosynthesis and leaf anatomy in the model species Arabidopsis thaliana (Col-0) grown under three different light intensities at two different leaf ages. We found that light × age interaction was significant for photosynthesis but not for anatomical characteristics. Increasing growth light intensities resulted in increases in leaf mass per area, thickness, number of palisade cell layers, and chloroplast area lining to intercellular airspace. Low and moderate-but not high-light intensity had a significant effect on all photosynthetic characteristics. Leaf aging was associated with increases in cell wall thickness (T ) in all light treatments and in increases in leaf thickness in plants grown under low and moderate light intensities. However, g did not vary with leaf aging, and photosynthesis only decreased with leaf age under moderate and high light, suggesting a compensatory effect between increased T and decreased chloroplast thickness on the total CO diffusion resistance.
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http://dx.doi.org/10.1111/ppl.13398DOI Listing
August 2021

Recent advances in understanding and improving photosynthesis.

Fac Rev 2020 6;9. Epub 2020 Nov 6.

Department of Biology, Universitat de les Illes Balears, INAGEA, Palma de Mallorca, Spain.

Since 1893, when the word "photosynthesis" was first coined by Charles Reid Barnes and Conway MacMillan, our understanding of the elements and regulation of this complex process is far from being entirely understood. We aim to review the most relevant advances in photosynthesis research from the last few years and to provide a perspective on the forthcoming research in this field. Recent discoveries related to light sensing, harvesting, and dissipation; kinetics of CO fixation; components and regulators of CO diffusion through stomata and mesophyll; and genetic engineering for improving photosynthetic and production capacities of crops are addressed.
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http://dx.doi.org/10.12703/b/9-5DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7886073PMC
November 2020

Decreased Levels of Thioredoxin Influences Stomatal Development and Aperture but Not Photosynthesis under Non-Stress and Saline Conditions.

Int J Mol Sci 2021 Jan 21;22(3). Epub 2021 Jan 21.

Department of Stress Biology and Plant Pathology, CEBAS-CSIC, 30100 Murcia, Spain.

Salinity has a negative impact on plant growth, with photosynthesis being downregulated partially due to osmotic effect and enhanced cellular oxidation. Redox signaling contributes to the plant response playing thioredoxins (TRXs) a central role. In this work we explore the potential contribution of Arabidopsis TRX1 to the photosynthetic response under salinity analyzing Arabidopsis wild-type (WT) and two mutant lines in their growth under short photoperiod and higher light intensity than previous reported works. Stomatal development and apertures and the antioxidant, hormonal and metabolic acclimation are also analyzed. In control conditions mutant plants displayed less and larger developed stomata and higher pore size which could underlie their higher stomatal conductance, without being affected in other photosynthetic parameters. Under salinity, all genotypes displayed a general decrease in photosynthesis and the oxidative status in the mutant lines was altered, with higher levels of HO and NO but also higher ascorbate/glutathione (ASC/GSH) redox states than WT plants. Finally, sugar changes and increases in abscisic acid (ABA) and NO may be involved in the observed higher stomatal response of the TRX1-altered plants. Therefore, the lack of affected stomata development and opening and the mutants modulate their antioxidant, metabolic and hormonal responses to optimize their adaptation to salinity.
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http://dx.doi.org/10.3390/ijms22031063DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7865980PMC
January 2021

Resurrection plants optimize photosynthesis despite very thick cell walls by means of chloroplast distribution.

J Exp Bot 2021 03;72(7):2600-2610

Research Group on Plant Biology under Mediterranean Conditions, Departament de Biologia, Universitat de les Illes Balears (UIB), INAGEA, Carretera de Valldemossa Km 7.5, 07122 Palma de Mallorca, Illes Balears, Spain.

Resurrection plants are vascular species able to sustain extreme desiccation in their vegetative tissues. Despite its potential interest, the role of leaf anatomy in CO2 diffusion and photosynthesis under non-stressed conditions has not been explored in these species. Net CO2 assimilation (An) and its underlying diffusive, biochemical, and anatomical determinants were assessed in 10 resurrection species from diverse locations, including ferns, and homoiochlorophyllous and poikilochlorophyllous angiosperms. Data obtained were compared with previously published results in desiccation-sensitive ferns and angiosperms. An in resurrection plants was mostly driven by mesophyll conductance to CO2 (gm) and limited by CO2 diffusion. Resurrection species had a greater cell wall thickness (Tcw) than desiccation-sensitive plants, a feature associated with limited CO2 diffusion in the mesophyll, but also greater chloroplast exposure to intercellular spaces (Sc), which usually leads to higher gm. This combination enabled a higher An per Tcw compared with desiccation-sensitive species. Resurrection species possess unusual anatomical features that could confer stress tolerance (thick cell walls) without compromising the photosynthetic capacity (high chloroplast exposure). This mechanism is particularly successful in resurrection ferns, which display higher photosynthesis than their desiccation-sensitive counterparts.
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http://dx.doi.org/10.1093/jxb/erab022DOI Listing
March 2021

Photosynthesis on the edge: photoinhibition, desiccation and freezing tolerance of Antarctic bryophytes.

Photosynth Res 2021 Aug 8;149(1-2):135-153. Epub 2020 Oct 8.

Department of Botany, Ecology and Plant Physiology, Universidad de La Laguna (ULL), 38200 La Laguna, Canarias, Spain.

In Antarctica, multiple stresses (low temperatures, drought and excessive irradiance) hamper photosynthesis even in summer. We hypothesize that controlled inactivation of PSII reaction centres, a mechanism widely studied by pioneer work of Fred Chow and co-workers, may effectively guarantee functional photosynthesis under these conditions. Thus, we analysed the energy partitioning through photosystems in response to temperature in 15 bryophyte species presenting different worldwide distributions but all growing in Livingston Island, under controlled and field conditions. We additionally tested their tolerance to desiccation and freezing and compared those with their capability for sexual reproduction in Antarctica (as a proxy to overall fitness). Under field conditions, when irradiance rules air temperature by the warming of shoots (up to 20 °C under sunny days), a predominance of sustained photoinhibition beyond dynamic heat dissipation was observed at low temperatures. Antarctic endemic and polar species showed the largest increases of photoinhibition at low temperatures. On the contrary, the variation of thermal dissipation with temperature was not linked to species distribution. Instead, maximum non-photochemical quenching at 20 °C was related (strongly and positively) with desiccation tolerance, which also correlated with fertility in Antarctica, but not with freezing tolerance. Although all the analysed species tolerated - 20 °C when dry, the tolerance to freezing in hydrated state ranged from the exceptional ability of Schistidium rivulare (that survived for 14 months at - 80 °C) to the susceptibility of Bryum pseudotriquetrum (that died after 1 day at - 20 °C unless being desiccated before freezing).
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http://dx.doi.org/10.1007/s11120-020-00785-0DOI Listing
August 2021

It Is Hot in the Sun: Antarctic Mosses Have High Temperature Optima for Photosynthesis Despite Cold Climate.

Front Plant Sci 2020 7;11:1178. Epub 2020 Aug 7.

Centre for Sustainable Ecosystem Solutions, School of Earth, Atmosphere and Life Sciences, University of Wollongong, Wollongong, NSW, Australia.

The terrestrial flora of Antarctica's frozen continent is restricted to sparse ice-free areas and dominated by lichens and bryophytes. These plants frequently battle sub-zero temperatures, extreme winds and reduced water availability; all influencing their ability to survive and grow. Antarctic mosses, however, can have canopy temperatures well above air temperature. At midday, canopy temperatures can exceed 15°C, depending on moss turf water content. In this study, the optimum temperature of photosynthesis was determined for six Antarctic moss species: , , , , , and collected from King George Island (maritime Antarctica) and/or the Windmill Islands, East Antarctica. Both chlorophyll fluorescence and gas exchange showed maximum values of electron transport rate occurred at canopy temperatures higher than 20°C. The optimum temperature for both net assimilation of CO and photoprotective heat dissipation of three East Antarctic species was 20-30°C and at temperatures below 10°C, mesophyll conductance did not significantly differ from 0. Maximum mitochondrial respiration rates occurred at temperatures higher than 35°C and were lower by around 80% at 5°C. Despite the extreme cold conditions that Antarctic mosses face over winter, the photosynthetic apparatus appears optimised to warm temperatures. Our estimation of the total carbon balance suggests that survival in this cold environment may rely on a capacity to maximize photosynthesis for brief periods during summer and minimize respiratory carbon losses in cold conditions.
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http://dx.doi.org/10.3389/fpls.2020.01178DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7457050PMC
August 2020

Cell wall composition and thickness affect mesophyll conductance to CO2 diffusion in Helianthus annuus under water deprivation.

J Exp Bot 2020 12;71(22):7198-7209

Research Group on Plant Biology under Mediterranean Conditions, Departament de Biologia, Universitat de les Illes Balears (UIB), INAGEA, Carretera de Valldemossa Km 7.5, 07122 Palma de Mallorca, Illes Balears, Spain.

Water deprivation affects photosynthesis, leaf anatomy, and cell wall composition. Although the former effects have been widely studied, little is known regarding those changes in cell wall major (cellulose, hemicelluloses, pectin, and lignin) and minor (cell wall-bound phenolics) compounds in plants acclimated to short- and long-term water deprivation and during recovery. In particular, how these cell wall changes impact anatomy and/or photosynthesis, specifically mesophyll conductance to CO2 diffusion (gm), has been scarcely studied. To induce changes in photosynthesis, cell wall composition and anatomy, Helianthus annuus plants were studied under five conditions: (i) control (i.e. without stress) (CL); (ii) long-term water deficit stress (LT); (iii) long-term water deficit stress with recovery (LT-Rec); (iv) short-term water deficit stress (ST); and (v) short-term water deficit stress with recovery (ST-Rec), resulting in a wide photosynthetic range (from 3.80 ± 1.05 μmol CO2 m-2 s-1 to 24.53 ± 0.42 μmol CO2 m-2 s-1). Short- and long-term water deprivation and recovery induced distinctive responses of the examined traits, evidencing a cell wall dynamic turnover during plants acclimation to each condition. In particular, we demonstrated for the first time how gm correlated negatively with lignin and cell wall-bound phenolics and how the (cellulose+hemicelloses)/pectin ratio was linked to cell wall thickness (Tcw) variations.
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http://dx.doi.org/10.1093/jxb/eraa413DOI Listing
December 2020

Reduced photosynthesis in Arabidopsis thaliana atpme17.2 and atpae11.1 mutants is associated to altered cell wall composition.

Physiol Plant 2021 Jul 25;172(3):1439-1451. Epub 2020 Aug 25.

Research Group on Plant Biology under Mediterranean Conditions, Departament de Biologia, Universitat de les Illes Balears (UIB) - Agro-Environmental and Water Economics Institute (INAGEA), Palma, 07122, Spain.

The cell wall is a complex and dynamic structure that determines plants' performance by constant remodeling of its compounds. Although cellulose is its major load-bearing component, pectins are crucial to determine wall characteristics. Changes in pectin physicochemical properties, due to pectin remodeling enzymes (PRE), induce the rearrangement of cell wall compounds, thus, modifying wall architecture. In this work, we tested for the first time how cell wall dynamics affect photosynthetic properties in Arabidopsis thaliana pectin methylesterase atpme17.2 and pectin acetylesterase atpae11.1 mutants in comparison to wild-type Col-0. Our results showed maintained PRE activities comparing mutants with wild-type and no significant differences in cellulose, but cell wall non-cellulosic neutral sugars contents changed. Particularly, the amount of galacturonic acid (GalA) - which represents to some extent the pectin cell wall proportion - was reduced in the two mutants. Additionally, physiological characterization revealed that mutants presented a decreased net CO assimilation (A ) because of reductions in both stomatal (g ) and mesophyll conductances (g ). Thus, our results suggest that atpme17.2 and atpae11.1 cell wall modifications due to genetic alterations could play a significant role in determining photosynthesis.
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http://dx.doi.org/10.1111/ppl.13186DOI Listing
July 2021

What drives photosynthesis during desiccation? Mosses and other outliers from the photosynthesis-elasticity trade-off.

J Exp Bot 2020 10;71(20):6460-6470

Research Group on Plant Biology under Mediterranean Conditions. Departament de Biologia, Universitat de les Illes Balears, INAGEA Carretera de Valldemossa Km 7.5, Palma de Mallorca, Illes Balears, Spain.

In vascular plants, more rigid leaves have been linked to lower photosynthetic capacity, associated with low CO2 diffusion across the mesophyll, indirectly resulting in a trade-off between photosynthetic capacity (An) and bulk modulus of elasticity (ε). However, we evaluated mosses, liverworts, and Chara sp., plus some lycophytes and ferns, and found that they behaved as clear outliers of the An-ε relationship. Despite this finding, when vascular and non-vascular plants were plotted together, ε still linearly determined the cessation of net photosynthesis during desiccation both in species with stomata (either actively or hydro-passively regulated) and in species lacking stomata, and regardless of their leaf structure. The latter result challenges our current view of photosynthetic responses to desiccation and/or water stress. Structural features and hydric strategy are discussed as possible explanations for the deviation of these species from the An-ε trade-off, as well as for the general linear dependency between ε and the full cessation of An during desiccation.
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http://dx.doi.org/10.1093/jxb/eraa328DOI Listing
October 2020

From one side to two sides: the effects of stomatal distribution on photosynthesis.

New Phytol 2020 12 28;228(6):1754-1766. Epub 2020 Aug 28.

Research Group on Plant Biology under Mediterranean Conditions, Universitat de les Illes Balears/Instituto de Investigaciones Agroambientales y de Economía del Agua (INAGEA), Carretera de Valldemossa Km 7.5, Palma de Mallorca, Illes Balears, 07121, Spain.

The functions of stomata have been studied for a long time; however, a clear understanding of the influences of stomatal distribution on photosynthesis, especially the CO diffusion, is still unclear. Here, we investigated the stomatal morphology, distribution on leaf surfaces, vein traits and gas exchange parameters of 61 species, of which 29 were amphistomatous, spanning 32 families. Photosynthesis (A) was tightly coupled with operational stomatal conductance (g ) and mesophyll conductance (g ) regardless of whether phylogenetic relationships were accounted for. Although the enhancement of g from ferns and gymnosperms to angiosperms could largely be explained by the increase in leaf vein density (VLA) and stomatal density (SD), the g was decoupled from VLA and SD across angiosperm species. Instead, A in angiosperms was further influenced by the allocation of stomatal pores on leaf surfaces, which dramatically increased g and g . Moreover, the ratio of g to anatomically based maximum g was, on average, 0.12 across species. Our results show that the shift of stomatal pores from one leaf side to both sides played an important role in regulating CO diffusion via both stomata and mesophyll tissues. Modifications of stomata distribution have potential as a functional trait for photosynthesis improvement.
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http://dx.doi.org/10.1111/nph.16801DOI Listing
December 2020

Cell wall composition strongly influences mesophyll conductance in gymnosperms.

Plant J 2020 08 3;103(4):1372-1385. Epub 2020 Jun 3.

Research Group in Plant Biology under Mediterranean Conditions, Universitat de les Illes Balears (UIB) - Agro-Environmental and Water Economics Institute (INAGEA), Palma, Illes Balears, 07122, Spain.

Cell wall thickness is widely recognized as one of the main determinants of mesophyll conductance to CO (g ). However, little is known about the components that regulate effective CO diffusivity in the cell wall (i.e. the ratio between actual porosity and tortuosity, the other two biophysical diffusion properties of cell walls). The aim of this study was to assess, at the interspecific level, potential relationships between cell wall composition, cell wall thickness (T ) and g . Gymnosperms constitute an ideal group to deepen these relationships, as they present, on average, the thickest cell walls within spermatophytes. We characterized the foliar gas exchange, the morphoanatomical traits related with g , the leaf fraction constituted by cell walls and three main components of primary cell walls (hemicelluloses, cellulose and pectins) in seven gymnosperm species. We found that, although the relatively low g of gymnosperms was mainly determined by their elevated T , g was also strongly correlated with cell wall composition, which presumably sets the final effective CO diffusivity. The data presented here suggest that (i) differences in g are strongly correlated to the pectins to hemicelluloses and cellulose ratio in gymnosperms, and (ii) variations in cell wall composition may modify effective CO diffusivity in the cell wall to compensate the negative impact of thickened walls. We speculate that higher relative pectin content allows higher g because pectins increase cell wall hydrophilicity and CO molecules cross the wall dissolved in water.
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http://dx.doi.org/10.1111/tpj.14806DOI Listing
August 2020

Mesophyll conductance: the leaf corridors for photosynthesis.

Biochem Soc Trans 2020 04;48(2):429-439

Research Group on Plant Biology Under Mediterranean Conditions, Department de Biologia, Universitat de les Illes Balears/Institute of Agro-Environmental Research and Water Economy -INAGEA, Carretera de Valldemossa, 07122 Palma de Mallorca, Spain.

Besides stomata, the photosynthetic CO2 pathway also involves the transport of CO2 from the sub-stomatal air spaces inside to the carboxylation sites in the chloroplast stroma, where Rubisco is located. This pathway is far to be a simple and direct way, formed by series of consecutive barriers that the CO2 should cross to be finally assimilated in photosynthesis, known as the mesophyll conductance (gm). Therefore, the gm reflects the pathway through different air, water and biophysical barriers within the leaf tissues and cell structures. Currently, it is known that gm can impose the same level of limitation (or even higher depending of the conditions) to photosynthesis than the wider known stomata or biochemistry. In this mini-review, we are focused on each of the gm determinants to summarize the current knowledge on the mechanisms driving gm from anatomical to metabolic and biochemical perspectives. Special attention deserve the latest studies demonstrating the importance of the molecular mechanisms driving anatomical traits as cell wall and the chloroplast surface exposed to the mesophyll airspaces (Sc/S) that significantly constrain gm. However, even considering these recent discoveries, still is poorly understood the mechanisms about signaling pathways linking the environment a/biotic stressors with gm responses. Thus, considering the main role of gm as a major driver of the CO2 availability at the carboxylation sites, future studies into these aspects will help us to understand photosynthesis responses in a global change framework.
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http://dx.doi.org/10.1042/BST20190312DOI Listing
April 2020

Fuelling life: recent advances in photosynthesis research.

Plant J 2020 02;101(4):753-755

Departament de, Universitat de les Illes Balears-INAGEA, Carretera de Valldemossa Km 7.5, Palma de Mallorca, 07122, Spain.

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http://dx.doi.org/10.1111/tpj.14698DOI Listing
February 2020

Nano and Micro Unmanned Aerial Vehicles (UAVs): A New Grand Challenge for Precision Agriculture?

Curr Protoc Plant Biol 2020 03;5(1):e20103

Grup de Recerca en Biologia de les Plantes en Condicions Mediterrànies, Departament de Biologia, University of the Balearic Islands (UIB)/Instituto de investigaciones Agroambientales y de la Economía del Agua (INAGEA), Palma, Spain.

By collecting data at spatial and temporal scales that are inaccessible to satellite and field observation, unmanned aerial vehicles (UAVs) are revolutionizing a number of scientific and management disciplines. UAVs may be particularly valuable for precision agricultural applications, offering strong potential to improve the efficiency of water, nutrient, and disease management. However, some authors have suggested that the UAV industry has overhyped the potential value of this technology for agriculture, given that it is difficult for non-specialists to operate UAVs as well as to process and interpret the resulting data. Here, we analyze the barriers to applying UAVs for precision agriculture, which range from regulatory issues to technical requirements. We then evaluate how new developments in the nano- and micro-UAV (NAV and MAV, respectively) markets may help to overcome these barriers. Among the possible breakthroughs that we identify is the ability of NAV/MAV platforms to directly quantify plant traits using methods (e.g., object-oriented classification) that require less image calibration and interpretation than spectral index-based approaches. We suggest that this potential, when combined with steady improvements in sensor miniaturization, flight precision, and autonomy as well as cloud-based image processing, will make UAVs a tool with much broader adoption by agricultural managers in the near future. If this wider uptake is realized, then UAVs have real potential to improve agriculture's resource-use efficiency. © 2020 by John Wiley & Sons, Inc.
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http://dx.doi.org/10.1002/cppb.20103DOI Listing
March 2020

Low-temperature tolerance of the Antarctic species Deschampsia antarctica: A complex metabolic response associated with nutrient remobilization.

Plant Cell Environ 2020 06 24;43(6):1376-1393. Epub 2020 Feb 24.

Research Group on Plant Biology under Mediterranean Conditions, Universitat de les Illes Balears (UIB)-Instituto de Agroecología y Economía del Agua (INAGEA), Palma de Mallorca, Spain.

The species Deschampsia antarctica (DA) is one of the only two native vascular species that live in Antarctica. We performed ecophysiological, biochemical, and metabolomic studies to investigate the responses of DA to low temperature. In parallel, we assessed the responses in a non-Antarctic reference species (Triticum aestivum [TA]) from the same family (Poaceae). At low temperature (4°C), both species showed lower photosynthetic rates (reductions were 70% and 80% for DA and TA, respectively) and symptoms of oxidative stress but opposite responses of antioxidant enzymes (peroxidases and catalase). We employed fused least absolute shrinkage and selection operator statistical modelling to associate the species-dependent physiological and antioxidant responses to primary metabolism. Model results for DA indicated associations with osmoprotection, cell wall remodelling, membrane stabilization, and antioxidant secondary metabolism (synthesis of flavonols and phenylpropanoids), coordinated with nutrient mobilization from source to sink tissues (confirmed by elemental analysis), which were not observed in TA. The metabolic behaviour of DA, with significant changes in particular metabolites, was compared with a newly compiled multispecies dataset showing a general accumulation of metabolites in response to low temperatures. Altogether, the responses displayed by DA suggest a compromise between catabolism and maintenance of leaf functionality.
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http://dx.doi.org/10.1111/pce.13737DOI Listing
June 2020

Photosynthesis and photosynthetic efficiencies along the terrestrial plant's phylogeny: lessons for improving crop photosynthesis.

Plant J 2020 02 24;101(4):964-978. Epub 2020 Jan 24.

Research Group on Plant Biology Under Mediterranean Conditions, Universitat de les Illes Balears - Instituto de Investigaciones Agroambientales y de Economía del Agua (UIB-INAGEA), Carretera de Valldemossa Km 7.5, 07122, Palma, Spain.

Photosynthesis is the basis of all life on Earth. Surprisingly, until very recently, data on photosynthesis, photosynthetic efficiencies, and photosynthesis limitations in terrestrial land plants other than spermatophytes were very scarce. Here we provide an updated data compilation showing that maximum photosynthesis rates (expressed either on an area or dry mass basis) progressively scale along the land plant's phylogeny, from lowest values in bryophytes to largest in angiosperms. Unexpectedly, both photosynthetic water (WUE) and nitrogen (PNUE) use efficiencies also scale positively through the phylogeny, for which it has been commonly reported that these two efficiencies tend to trade-off between them when comparing different genotypes or a single species subject to different environmental conditions. After providing experimental evidence that these observed trends are mostly due to an increased mesophyll conductance to CO - associated with specific anatomical changes - along the phylogeny, we discuss how these findings on a large phylogenetic scale can provide useful information to address potential photosynthetic improvements in crops in the near future.
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http://dx.doi.org/10.1111/tpj.14651DOI Listing
February 2020

Cell wall components regulate photosynthesis and leaf water relations of Vitis vinifera cv. Grenache acclimated to contrasting environmental conditions.

J Plant Physiol 2020 Jan 26;244:153084. Epub 2019 Nov 26.

Research Group on Plant Biology under Mediterranean Conditions, Departament de Biologia, Universitat de les Illes Balears (UIB), INAGEA, Carretera de Valldemossa Km 7.5, 07122 Palma de Mallorca, Illes Balears, Spain. Electronic address:

Environmental conditions determine plants performance as they shape - among other key factors - leaf features and physiology. However, little is known regarding to the changes occurring in leaf cell wall composition during the acclimation to an environmental stress and, specially, if these changes have an impact on other leaf physiology aspects. In order to induce changes in photosynthesis, leaf water relations and cell wall main components (i.e., cellulose, hemicelluloses and pectins) and see how they co-vary, Vitis vinifera cv. Grenache was tested under four different conditions: (i) non-stress conditions (i.e., control, with high summer temperature and irradiance), (ii) growth chamber conditions, (iii) growth chamber under water stress and (iv) cold growth chamber. Plants developed in growth chambers decreased net CO assimilation (A) and mesophyll conductance (g) compared to control. Although cold did not change the bulk modulus of elasticity (ε), it decreased in growth chamber conditions and water stress. Control treatment showed the highest values for photosynthetic parameters and ε as well as for leaf structural traits such as leaf mass area (LMA) and leaf density (LD). Whereas cellulose content correlated with photosynthetic parameters, particularly A and g, pectins and the amount of alcohol insoluble residue (AIR) - an approximation of the isolated cell wall fraction - correlated with leaf water parameters, specifically, ε. Although preliminary, our results suggest that cell wall modifications due to environmental acclimations can play a significant role in leaf physiology by affecting distinctly photosynthesis and water relations in a manner that might depend on environmental conditions.
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http://dx.doi.org/10.1016/j.jplph.2019.153084DOI Listing
January 2020

Cytochrome respiration pathway and sulphur metabolism sustain stress tolerance to low temperature in the Antarctic species Colobanthus quitensis.

New Phytol 2020 01 21;225(2):754-768. Epub 2019 Oct 21.

Research Group on Plant Biology under Mediterranean Conditions, Instituto de Agroecología y Economía del Agua (INAGEA), Universitat de les Illes Balears (UIB), cta. Valldemossa km 7,5, 07122, Palma de Mallorca, Spain.

Understanding the strategies employed by plant species that live in extreme environments offers the possibility to discover stress tolerance mechanisms. We studied the physiological, antioxidant and metabolic responses to three temperature conditions (4, 15, and 23°C) of Colobanthus quitensis (CQ), one of the only two native vascular species in Antarctica. We also employed Dianthus chinensis (DC), to assess the effects of the treatments in a non-Antarctic species from the same family. Using fused LASSO modelling, we associated physiological and biochemical antioxidant responses with primary metabolism. This approach allowed us to highlight the metabolic pathways driving the response specific to CQ. Low temperature imposed dramatic reductions in photosynthesis (up to 88%) but not in respiration (sustaining rates of 3.0-4.2 μmol CO  m  s ) in CQ, and no change in the physiological stress parameters was found. Its notable antioxidant capacity and mitochondrial cytochrome respiratory activity (20 and two times higher than DC, respectively), which ensure ATP production even at low temperature, was significantly associated with sulphur-containing metabolites and polyamines. Our findings potentially open new biotechnological opportunities regarding the role of antioxidant compounds and respiratory mechanisms associated with sulphur metabolism in stress tolerance strategies to low temperature.
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http://dx.doi.org/10.1111/nph.16167DOI Listing
January 2020

Photosynthesis Optimized across Land Plant Phylogeny.

Trends Plant Sci 2019 10 27;24(10):947-958. Epub 2019 Jul 27.

Research Group on Plant Biology under Mediterranean conditions, Departament de Biologia, Universitat de les Illes Balears / Institute of Agro-Environmental Research and Water Economy -INAGEA, Carretera de Valldemossa, 07122, Palma, Spain. Electronic address:

Until recently, few data were available on photosynthesis and its underlying mechanistically limiting factors in plants, other than crops and model species. Currently, a new large pool of data from extant representatives of basal terrestrial plant groups is emerging, allowing exploration of how photosynthetic capacity (A) increases from minimum values in bryophytes to maximum in tracheophytes, which is associated to an optimization of the balance between its limiting factors. From predominant mesophyll conductance limitation (l) in bryophytes and lycophytes (fern allies) to stomatal conductance (l) and l colimitation in pteridophytes (ferns) and gymnosperms, a balanced colimitation by the three limitations is finally reached in angiosperms. We discuss the implications of this new knowledge for future biotechnological attempts to improve crop photosynthesis.
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http://dx.doi.org/10.1016/j.tplants.2019.07.002DOI Listing
October 2019

The apoplastic antioxidant system and altered cell wall dynamics influence mesophyll conductance and the rate of photosynthesis.

Plant J 2019 09 15;99(6):1031-1046. Epub 2019 Jul 15.

Research Group on Plant Biology under Mediterranean Conditions, Universitat de les Illes Balears (UIB)-Instituto de Agroecología y Economía del Agua (INAGEA), ctra. Valldemossa km 7,5, Palma de Mallorca, Spain.

Mesophyll conductance (g ), the diffusion of CO from substomatal cavities to the carboxylation sites in the chloroplasts, is a highly complex trait driving photosynthesis (net CO assimilation, A ). However, little is known concerning the mechanisms by which it is dynamically regulated. The apoplast is considered as a 'key information bridge' between the environment and cells. Interestingly, most of the environmental constraints affecting g also cause apoplastic responses, cell wall (CW) alterations and metabolic rearrangements. Since CW thickness is a key determinant of g , we hypothesize that other changes in this cellular compartiment should also influence g . We study the relationship between the antioxidant apoplastic system and CW metabolism and the g responses in tobacco plants (Nicotiana sylvestris L.) under two abiotic stresses (drought and salinity), combining in vivo gas-exchange measurements with analyses of antioxidant activities, CW composition and primary metabolism. Stress treatments imposed substantial reductions in A (58-54%) and g (59%), accompanied by a strong antioxidant enzymatic response at the apoplastic and symplastic levels. Interestingly, apoplastic but not symplastic peroxidases were positively related to g . Leaf anatomy remained mostly stable; however, the stress treatments significantly affected the CW composition, specifically pectins, which showed significant relationships with A and g . The treatments additionally promoted a differential primary metabolic response, and specific CW-related metabolites including galactose, glucosamine and hydroxycinnamate showed exclusive relationships with g independent of the stress. These results suggest that g responses can be attributed to specific changes in the apoplastic antioxidant system and CW metabolism, opening up more possibilities for improving photosynthesis using breeding/biotechnological strategies.
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http://dx.doi.org/10.1111/tpj.14437DOI Listing
September 2019

Anatomical constraints to nonstomatal diffusion conductance and photosynthesis in lycophytes and bryophytes.

New Phytol 2019 05 3;222(3):1256-1270. Epub 2019 Feb 3.

Research Group on Plant Biology under Mediterranean Conditions, Universitat de les Illes Balears (UIB) - Instituto de Investigaciones Agroambientales y de Economía del Agua (INAGEA), Carretera de Valldemossa Km 7.5, 07122, Palma, Illes Balears, Spain.

Photosynthesis in bryophytes and lycophytes has received less attention than terrestrial plant groups. In particular, few studies have addressed the nonstomatal diffusion conductance to CO g of these plant groups. Their lower photosynthetic rate per leaf mass area at any given nitrogen concentration compared with vascular plants suggested a stronger limitation by CO diffusion. We hypothesized that bryophyte and lycophyte photosynthesis is largely limited by low g . Here, we studied CO diffusion inside the photosynthetic tissues and its relationships with photosynthesis and anatomical parameters in bryophyte and lycophyte species in Antarctica, Australia, Estonia, Hawaii and Spain. On average, lycophytes and, specially, bryophytes had the lowest photosynthetic rates and nonstomatal diffusion conductance reported for terrestrial plants. These low values are related to their very thick cell walls and their low exposure of chloroplasts to cell perimeter. We conclude that the reason why bryophytes lie at the lower end of the leaf economics spectrum is their strong nonstomatal diffusion conductance limitation to photosynthesis, which is driven by their specific anatomical characteristics.
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http://dx.doi.org/10.1111/nph.15675DOI Listing
May 2019

A field portable method for the semi-quantitative estimation of dehydration tolerance of photosynthetic tissues across distantly related land plants.

Physiol Plant 2019 Dec 25;167(4):540-555. Epub 2019 Mar 25.

Department Plant Biology and Ecology, University of the Basque Country (UPV/EHU), Leioa, Spain.

Desiccation tolerant (DT) plants withstand complete cellular dehydration, reaching relative water contents (RWC) below 30% in their photosynthetic tissues. Desiccation sensitive (DS) plants exhibit different degrees of dehydration tolerance (DHT), never surviving water loss >70%. To date, no procedure for the quantitative evaluation of DHT extent exists that is able to discriminate DS species with differing degrees of DHT from truly DT plants. We developed a simple, feasible and portable protocol to differentiate between DT and different degrees of DHT in the photosynthetic tissues of seed plants and between fast desiccation (< 24 h) tolerant (FDT) and sensitive (FDS) bryophytes. The protocol is based on (1) controlled desiccation inside Falcon tubes equilibrated at three different relative humidities that, consequently, induce three different speeds and extents of dehydration and (2) an evaluation of the average percentage of maximal photochemical efficiency of PSII (F /fm) recovery after rehydration. Applying the method to 10 bryophytes and 28 tracheophytes from various locations, we found that (1) imbibition of absorbent material with concentrated salt-solutions inside the tubes provides stable relative humidity and avoids direct contact with samples; (2) for 50 ml capacity tubes, the optimal plant amount is 50-200 mg fresh weight; (3) the method is useful in remote locations due to minimal instrumental requirements; and (4) a threshold of 30% recovery of the initial F /fm upon reaching RWC ≤ 30% correctly categorises DT species, with three exceptions: two poikilochlorophyllous species and one gymnosperm. The protocol provides a semi-quantitative expression of DHT that facilitates comparisons of species with different morpho-physiological traits and/or ecological attributes.
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http://dx.doi.org/10.1111/ppl.12890DOI Listing
December 2019

Leaf economics spectrum in rice: leaf anatomical, biochemical, and physiological trait trade-offs.

J Exp Bot 2018 11;69(22):5599-5609

Research Group on Plant Biology under Mediterranean conditions, Instituto de Investigaciones Agroambientales y de Economía del Agua (INAGEA)-Universitat de les Illes Balears (UIB), Palma de Mallorca, Illes Balears, Spain.

The leaf economics spectrum (LES) is an ecophysiological concept describing the trade-offs of leaf structural and physiological traits, and has been widely investigated on multiple scales. However, the effects of the breeding process on the LES in crops, as well as the mechanisms of the trait trade-offs underlying the LES, have not been thoroughly elucidated to date. In this study, a dataset that included leaf anatomical, biochemical, and functional traits was constructed to evaluate the trait covariations and trade-offs in domesticated species, namely rice (Oryza species). The slopes and intercepts of the major bivariate correlations of the leaf traits in rice were significantly different from the global LES dataset (Glopnet), which is based on multiple non-crop species in natural ecosystems, although the general patterns were similar. The photosynthetic traits responded differently to leaf structural and biochemical changes, and mesophyll conductance was the most sensitive to leaf nitrogen (N) status. A further analysis revealed that the relative limitation of mesophyll conductance declined with leaf N content; however, the limitation of the biochemistry increased relative to leaf N content. These findings indicate that breeding selection and high-resource agricultural environments lead crops to deviate from the leaf trait covariation in wild species, and future breeding to increase the photosynthesis of rice should primarily focus on improvement of the efficiency of photosynthetic enzymes.
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http://dx.doi.org/10.1093/jxb/ery322DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6255696PMC
November 2018

Mesophyll conductance in cotton bracts: anatomically determined internal CO2 diffusion constraints on photosynthesis.

J Exp Bot 2018 11;69(22):5433-5443

The Key Laboratory of Oasis Eco-agriculture, Xinjiang Production and Construction Group, Shihezi University, Shihezi, P.R. China.

Mesophyll conductance (gm) has been shown to affect photosynthetic capacity and thus the estimates of terrestrial carbon balance. While there have been some attempts to model gm at the leaf and larger scales, the potential contribution of gm to the photosynthesis of non-leaf green organs has not been studied. Here, we investigated the influence of gm on photosynthesis of cotton bracts and how it in turn is influenced by anatomical structures, by comparing leaf palisade and spongy mesophyll with bract tissue. Our results showed that photosynthetic capacity in bracts is much lower than in leaves, and that gm is a limiting factor for bract photosynthesis to a similar extent to stomatal conductance. Bract and the spongy tissue of leaves have lower mesophyll conductance than leaf palisade tissue due to the greater volume fraction of intercellular air spaces, smaller chloroplasts, lower surface area of mesophyll cells and chloroplasts exposed to leaf intercellular air spaces and, perhaps, lower membrane permeability. Comparing bracts with leaf spongy tissue, although bracts have a larger cell wall thickness, they have a similar gm estimated from anatomical characteristics, likely due to the cumulative compensatory effects of subtle differences in each subcellular component, especially chloroplast traits. These results provide the first evidence for anatomical constraints on gm and photosynthesis in non-leaf green organs.
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http://dx.doi.org/10.1093/jxb/ery296DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6255706PMC
November 2018
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