Publications by authors named "Melinda J Waterman"

6 Publications

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Limitations to photosynthesis in bryophytes: certainties and uncertainties regarding methodology.

J Exp Bot 2022 May 7. Epub 2022 May 7.

Universitat de les Illes Balears, Department of Biology, INAGEA. Carretera de Valldemossa Km 7.5, 07122, Palma de Mallorca, Illes Balears, Spain.

Bryophytes are the group of land plants with the lowest photosynthetic rates, which was considered to be a consequence of their higher anatomical CO2 diffusional limitation compared with tracheophytes. However, the most recent studies assessing limitations due to biochemistry and mesophyll conductance in bryophytes reveal discrepancies based on methodology used. In this study, we compared data calculated from two different methodologies for estimating mesophyll conductance: variable J and the curve-fitting method. Although correlated, mesophyll conductance estimated by the curve-fitting method was on average 4-fold higher than the conductance obtained by the variable J method; a large enough difference to account for the scale of differences previously shown between the biochemical and diffusional limitations to photosynthesis. Biochemical limitations were predominant when the curve-fitting method was used. We also demonstrated that variations in bryophyte relative water content during measurements can also introduce errors in the estimation of mesophyll conductance, especially for samples which are overly desiccated. Furthermore, total chlorophyll concentration and soluble proteins were significantly lower in bryophytes than in tracheophytes and the percentage of proteins quantified as rubisco was also significantly lower in bryophytes (less than 6.3% in all studied species) than in angiosperms (more than 16% in all non-stressed cases). Photosynthetic rates normalized by rubisco were not significantly different between bryophytes and angiosperms. Our data suggest that the biochemical limitation to photosynthesis in bryophytes is more relevant than so far assumed.
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http://dx.doi.org/10.1093/jxb/erac189DOI Listing
May 2022

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

UV-B and Drought Stress Influenced Growth and Cellular Compounds of Two Cultivars of Phaseolus vulgaris L. (Fabaceae).

Photochem Photobiol 2021 01 5;97(1):166-179. Epub 2020 Sep 5.

Department of Botany, Institute of Biosciences, University of São Paulo, São Paulo, SP, Brazil.

Combined enhanced UV-B radiation and drought may induce different morphological and physiological alterations in plants than either abiotic stress alone. We evaluated morphology, biomass, and primary and secondary metabolism changes in seedlings of two common bean cultivars, IAC Imperador (drought-resistant) and IAC Milênio. To test the hypothesis that cultivars responded differently to combined stresses in a controlled environment, seedlings of the examined been cultivars were exposed to UV-B and/or drought treatments for three weeks. The cultivars behaved differently, especially to the drought treatment, suggesting that they use different mechanisms to cope with unfavorable environmental conditions. IAC Imperador showed a stronger protective response, modifying wax composition and primary metabolism, and improving its resistance to UV-B radiation. For IAC Imperador, the accumulation of cuticular wax and alkane was higher under combined stress but production of primary alcohols was reduced, suggesting a possible fatty acyl switch. Root/shoot length and biomass ratios increased in both cultivars, particularly for the combined stress, indicating a common plant response. We show that these two bean cultivars responded more strongly to UV-B and combined stress than drought alone as evident in changes to their chemistry and biology. This shows the importance of investigating plant morphological and physiological responses to combined stress.
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http://dx.doi.org/10.1111/php.13318DOI Listing
January 2021

Photoprotection enhanced by red cell wall pigments in three East Antarctic mosses.

Biol Res 2018 Nov 21;51(1):49. Epub 2018 Nov 21.

Centre for Sustainable Ecosystem Solutions, School of Biological Sciences, University of Wollongong, Northfields Avenue, Wollongong, NSW, 2522, Australia.

Background: Antarctic bryophytes (mosses and liverworts) are resilient to physiologically extreme environmental conditions including elevated levels of ultraviolet (UV) radiation due to depletion of stratospheric ozone. Many Antarctic bryophytes synthesise UV-B-absorbing compounds (UVAC) that are localised in their cells and cell walls, a location that is rarely investigated for UVAC in plants. This study compares the concentrations and localisation of intracellular and cell wall UVAC in Antarctic Ceratodon purpureus, Bryum pseudotriquetrum and Schistidium antarctici from the Windmill Islands, East Antarctica.

Results: Multiple stresses, including desiccation and naturally high UV and visible light, seemed to enhance the incorporation of total UVAC including red pigments in the cell walls of all three Antarctic species analysed. The red growth form of C. purpureus had significantly higher levels of cell wall bound and lower intracellular UVAC concentrations than its nearby green form. Microscopic and spectroscopic analyses showed that the red colouration in this species was associated with the cell wall and that these red cell walls contained less pectin and phenolic esters than the green form. All three moss species showed a natural increase in cell wall UVAC content during the growing season and a decline in these compounds in new tissue grown under less stressful conditions in the laboratory.

Conclusions: UVAC and red pigments are tightly bound to the cell wall and likely have a long-term protective role in Antarctic bryophytes. Although the identity of these red pigments remains unknown, our study demonstrates the importance of investigating cell wall UVAC in plants and contributes to our current understanding of UV-protective strategies employed by particular Antarctic bryophytes. Studies such as these provide clues to how these plants survive in such extreme habitats and are helpful in predicting future survival of the species studied.
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http://dx.doi.org/10.1186/s40659-018-0196-1DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6247747PMC
November 2018

Antarctic Moss Biflavonoids Show High Antioxidant and Ultraviolet-Screening Activity.

J Nat Prod 2017 08 7;80(8):2224-2231. Epub 2017 Aug 7.

School of Chemistry, UNSW , Sydney, NSW 2052, Australia.

Ceratodon purpureus is a cosmopolitan moss that survives some of the harshest places on Earth: from frozen Antarctica to hot South Australian deserts. In a study on the survival mechanisms of the species, nine compounds were isolated from Australian and Antarctic C. purpureus. This included five biflavonoids, with complete structural elucidation of 1 and 2 reported here for the first time, as well as an additional four known phenolic compounds. Dispersion-corrected DFT calculations suggested a rotational barrier, leading to atropisomerism, resulting in the presence of diastereomers for compound 2. All isolates absorbed strongly in the ultraviolet (UV) spectrum, e.g., biflavone 1 (UV-A, 315-400 nm), which displayed the strongest radical-scavenging activity, 13% more efficient than the standard rutin; p-coumaric acid and trans-ferulic acid showed the highest UV-B (280-315 nm) absorption. The more complex and abundant 1 and 2 presumably have dual roles as both UV-screening and antioxidant compounds. They are strongly bound to Antarctic moss cell walls as well as located inside the cells of moss from both locations. The combined high stability and photoprotective abilities of these isolates may account for the known resilience of this species to UV-B radiation and its survival in some of the toughest locations in the world.
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http://dx.doi.org/10.1021/acs.jnatprod.7b00085DOI Listing
August 2017

Native hemiparasite and light effects on photoprotection and photodamage in a native host.

Funct Plant Biol 2015 Dec;42(12):1168-1178

Northumberland Building Rm NB260, Faculty of Health and Life Sciences, Northumbria University, NE1 8ST, UK.

Plants infected with hemiparasites often have lowered rates of photosynthesis, which could make them more susceptible to photodamage. However, it is also possible that infected plants increase their photoprotective capacity by changing their pigment content and/or engagement of the xanthophyll cycle. There are no published studies investigating infection effects on host pigment dynamics and how this relates to host susceptibility to photodamage whether in high (HL) or low light (LL). A glasshouse experiment was conducted where Leptospermum myrsinoides Schltdl. either uninfected or infected with Cassytha pubescens R.Br. was grown in HL or LL and pigment content of both host and parasite were assessed. Infection with C. pubescens significantly decreased all foliar pigment concentrations (except chlorophyll b) in L. myrsinoides in both HL and LL. Xanthophyll cycle (violaxanthin, antheraxanthin, zeaxanthin; VAZ) and chlorophyll (Chl) pigments decreased in parallel in response to infection, hence, VAZ/Chl of the host was unaffected by C. pubescens in either HL or LL. Pre-dawn and midday de-epoxidation state [(A+Z)/(V+A+Z)] of L. myrsinoides was also unaffected by infection in both HL and LL. Thus, L. myrsinoides infected with C. pubescens maintained similar photoprotective capacity per unit chlorophyll and engagement of the xanthophyll cycle as uninfected plants. Even though midday quantum yield (ΦPSII) of HL plants was affected by infection, pre-dawn maximum quantum yields (Fv/Fm) of hosts were the same as uninfected plants whether in HL or LL. This ability of L. myrsinoides to maintain photoprotective capacity/engagement when infected by C. pubescens thereby preventing photodamage could explain this host's tolerance to hemiparasite infection.
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http://dx.doi.org/10.1071/FP15132DOI Listing
December 2015
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