Annual variation in photo acclimation and photoprotection of the photobiont in the foliose lichen Xanthoria parietina.
Seasonal variation in maximal photochemical quantum yield (F(V)/F(M)) of photosystem II (PS II), light adapted quantum yield (Phi(II)) of PS II, non-photochemical quenching (NPQ), contents of chlorophylls, and xanthophyll cycle pigments (VAZ) was studied in Xanthoria parietina repeatedly sampled in one location in S Norway during one year. The seasonal course in the susceptibility to photoinhibition was evaluated as high light-induced changes (1,800 micromol photons m(-2) s(-1) for 24h) in F(V)/F(M), Phi(II), and NPQ, measured as the ability to recover after 2 and 20 h at low light in control thalli with a natural cortical parietin screen, and in thalli from which parietin had been removed prior to high light exposures. F(V)/F(M), Phi(II), chlorophyll content, and the conversion state of VAZ (DEPS) reached minimum in spring. At the same time, yearly maxima of VAZ content and NPQ were recorded. Thereafter, F(V)/F(M), Phi(II), and chlorophyll content increased gradually, reaching maximum values in late autumn. DEPS peaked already in summer. Similarly, VAZ and NPQ decreased from early summer until winter. All data show that the X. parietina photobiont acclimates to seasonal changes in solar radiation, consistent with the lichen's preference for well-lit habitats. However, a comparison with a study of seasonal acclimation in the X. parietina mycobiont shows that in order to understand the seasonal photobiont acclimation, one has to consider the seasonal variation in internal screening caused by the fungal regulation of the PAR-absorbing parietin. A joint effort of both bionts seems to be required to avoid serious photoinhibition.
Vráblíková
Hana
H
Department of Ecology and Natural Resource Management (Urbygningen), Norwegian University of Life Sciences, P.O. Box 5003, N-1432 As, Norway. vrablik@sci.muni.cz
McEvoy
Maria
M
Solhaug
Knut Asbjørn
KA
Barták
Milos
M
Gauslaa
Yngvar
Y
D000064:Acclimatization; D002734:Chlorophyll / Q000378:metabolism; D008011:Lichens / Q000502:physiology* / Q000528:radiation effects*; D009664:Norway; D018462:Photobiology; D010777:Photochemistry; D045332:Photosystem II Protein Complex / Q000378:metabolism; D012621:Seasons; D013559:Symbiosis; D024341:Xanthophylls / Q000378:metabolism; D065146:Zeaxanthins
D045332:Photosystem II Protein Complex; D024341:Xanthophylls; D065146:Zeaxanthins; D002734:Chlorophyll