A comparative study of wavelength-dependent photoinactivation in photosystem II of drought-tolerant photosynthetic organisms in Antarctica and the potential risks of photoinhibition in the habitat.

Background and Aims: All photosynthetic organisms are faced with photoinhibition, which would lead to death in severe environments. Because light quality and light intensity fluctuate dynamically in natural microenvironments, quantitative and qualitative analysis of photoinhibition is important to clarify how this environmental pressure has impacted ecological behaviour in different organisms. Methods: We evaluated the wavelength dependency of photoinactivation to photosystem II (PSII) of Prasiola crispa (green alga), Umbilicaria decussata (lichen) and Ceratodon purpureus (bryophyte) harvested from East Antarctica. For evaluation, we calculated reaction coefficients, Epis, of PSII photoinactivation against energy dose using a large spectrograph. Daily fluctuation of the rate coefficient of photoinactivation, kpi, was estimated from Epis and ambient light spectra measured during the summer season. Key Results: Wavelength dependency of PSII photoinactivation was different for the three species, although they form colonies in close proximity to each other in Antarctica. The lichen exhibited substantial resistance to photoinactivation at all wavelengths, while the bryophyte showed sensitivity only to UV-B light (<325 nm). On the other hand, the green alga, P. crispa, showed ten times higher Epi to UV-B light than the bryophyte. It was much more sensitive to UV-A (325-400 nm). The risk of photoinhibition fluctuated considerably throughout the day. On the other hand, Epis were reduced dramatically for dehydrated compared with hydrated P. crispa. Conclusions: The deduced rate coefficients of photoinactivation under ambient sunlight suggested that P. crispa needs to pay a greater cost to recover from photodamage than the lichen or the bryophyte in order to keep sufficient photosynthetic activity under the Antarctic habitat. A newly identified drought-induced protection mechanism appears to operate in P. crispa, and it plays a critical role in preventing the oxygen-evolving complex from photoinactivation when the repair cycle is inhibited by dehydration.

Restriction of sexual reproduction in the moss Racomitrium lanuginosum along an elevational gradient.

Terrestrial plant populations located at the margins of species' distributions often display reduced sexual reproduction and an increased reliance on asexual reproduction. One hypothesis to explain this phenomenon is that the decline is associated with environmental effects on the energetic costs to produce reproductive organs.In order to clarify the changing processes of sexual reproduction along an elevational gradient, we investigated the sexual reproductive parameters, such as the number of sporophytes and gametangia, in Racomitrium lanuginosum, a dioicous moss found on Mt. Fuji.Matured sporophytes were present only below 3,000 m, and the number of sporophytes per shoot tended to be lower at higher elevation habitats. The numbers of male inflorescences per shoot and antheridia per inflorescence and shoot significantly decreased with increasing elevation. In contrast, the numbers of female inflorescences per shoot and archegonia per inflorescence and shoot varied little across elevations. Synthesis. Our results suggest that the reasons for this limitation are assumed to be limitations in sporophyte development that result in abortion, and the spatial segregation between males and females. Possible reasons for the abortion of sporophytes are the inhibitory effects of low air temperature, a shortened growth period, and winter environmental conditions at higher elevations. Remarkable differences between male and female on various reproductive parameters found in this study are thought to affect the mode of sexual reproduction under the harsh environment. These differences between males and females may be caused by differences in the costs of production and development of gametangia, sensitivity to environmental stressors, and phenological patterns.