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, 51 (1), 49

Photoprotection Enhanced by Red Cell Wall Pigments in Three East Antarctic Mosses

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Photoprotection Enhanced by Red Cell Wall Pigments in Three East Antarctic Mosses

Melinda J Waterman et al. Biol Res.

Abstract

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.

Keywords: Antarctic moss; Anthocyanins; Bryophyte; Bryum pseudotriquetrum; Cell wall; Ceratodon purpureus; FT-IR; Schistidium antarctici; UV-B-absorbing compounds.

Figures

Fig. 1
Fig. 1
UV-B-absorbing compounds and anthocyanins in adjacent exposed (red) and shaded (green) moss samples. Comparison of mean total concentrations of a intracellular, cell wall and total UV-B-absorbing compounds are in terms of area under the curve between 280 and 315 nm (AUC280–315) mg−1 dry wt and b anthocyanin concentrations (n = 12 pairs). Bars are means (± SEM). Significant differences within extract types are marked with an asterisk. NB: Although the 1 SEM errors overlap for the cell wall bars, samples that are paired (and not independent) can show significant differences when the difference between them gives a small margin of error of its confidence interval. This consequently reflects a high correlation, which is taken into account in the statistics
Fig. 2
Fig. 2
Colour and UV-B-absorbing compound localisation differences between exposed (red) and shaded (green) Antarctic C. purpureus. a Photographs of red and green gametophyte photosynthetic tips. Light microscopy images of b red and c green leaves. Confocal microscopy fluorescence images of d red and e green leaves stained with Naturstoff reagent A to visualise the location of UV-B-absorbing compounds. Yellow/orange fluorescence indicates the presence of phenolic compounds. Scale bars in be are 25 μm
Fig. 3
Fig. 3
Intracellular, cell wall and total UV-B-absorbing compound concentrations for Antarctic Bryum pseudotriquetrumCeratodon purpureus and Schistidium antarctici collected at the beginning (December 2011) and middle (January 2012) of the austral summer season. Bars represent means (± SE). Significant differences within species are marked by asterisks (see Table 2)
Fig. 4
Fig. 4
Mean (± SE) concentrations of UV-B absorbing compounds within intracellular and cell wall extracts of exposed (red) Antarctic B. pseudotriquetrum, C. purpureus and S. antarctici grown in reduced light, with hydration and warm temperatures for 2 weeks in the laboratory (n = 6). Bars within extract type that are not connected by the same letter are significantly different (Table 3). Asterisk indicates a significant difference at P < 0.05 where post hoc tests showed no significant difference
Fig. 5
Fig. 5
Confocal fluorescence and transmission images showing qualitative concentrations (fluorescence intensity) and location of phenolic compounds within cells and cell walls of red varieties of Antarctic B. pseudotriquetrum, C. purpureus and S. antarctici at week 0 and after 2 weeks of growth in the laboratory (green samples, conditions as in Fig. 4). Leaves were stained with Naturstoff reagent A and fluorescence images were captured in the 500530 nm emission window under the same confocal settings. Yellow/orange fluorescence indicates the presence and concentration of phenolic compounds. Scale bars are 25 μm

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