Photoinhibition of photosynthesis in Antarctic lichen Usnea antarctica. I. Light intensity- and light duration-dependent changes in functioning of photosystem II

Abstract

The paper deals with the differences in sensitivity of Antarctic lichen to photoinhibition. Thalli of Usnea antarctica were collected at the James Ross Island, Antarctica (57°52´57´´W, 63°48´02´´S) and transferred in dry state to the Czech Republic. After rewetting in a laboratory, they were exposed to 2 high light treatments: short-term (30 min), and long-term (6 h). In short-term treatment, the sample were exposed to 1000 and 2000 µmol m -2 s -1 of photosynthetically active radiation (PAR). In long-term experiment, PAR of 300, 600, and 1000 µmol m -2 s -1 were used. Photosynthetic efficiency of U. antarctica thalli was monitored by chlorophyll fluorescence parameters, potential (F V /F M ) and actual ( PSII ) quantum yield of photochemical processes in photosystem II in particular. In short-term treatments, the F 0 , F V and F M signals, as well as the values of F V /F M , and  PSII showed light-induced decrease, however substantial recovery after consequent 30 min. in dark. Longer exposition (60 min) to high light led to more pronounced decrease in chlorophyll fluorescence than after 30 min treatment, however dark recovery was faster in the thalli treated before for longer time (60 min). Long-term treatment by high light caused gradual decrease in F V /F M and  PSII with the time of exposition. The extent of the decrease was found light dose-dependent. The time course was biphasic for F V /F M but not for  PSII . The study showed that wet thalli of Usnea antarctica had high capacity of photoprotective mechanisms to cope well either with short-or long-term high light stress. This might be of particular importance in the field at the James Ross Island, particularly at the begining of growing season when melting water is available and, simultaneously, high light stress may happen on fully sunny days. 43

Photoinhibition of photosynthesis in Antarctic lichen Usnea antarctica. II. Analysis of non-photochemical quenching mechanisms activated by low to medium light doses

“…Maksimov et al 2014). In studies focused on photoinhibition that exploit chlorophyll fluorescence kinetics supplemented with quenching analysis, lichens show a rapid recovery (in terms of hours) of functioning of PS II to pre-photoinhibitory status after termination of high light stress as shown for Usnea antarctica in our previous study (Barták et al 2012).…”

“…The main aim of this study is to compare the negative effects of short-and long-term exposition of Usnea antarctica caused by high light using a chlorophyll fluorescence approach. In previous paper (Barták et al 2012), we focused on negative effects of a short-term photoinhibitory treatment on PS II, F V /F M ,  PSII in particular. In the follow-up study, we paid attention to the activation of physiological mechanisms forming non-photochemical quenching of absorbed light energy.…”

Effects of short-term low temperature stress on chlorophyll fluorescence transients in Antarctic lichen species

“…Whenever ATP and NADPH consuption increases thanks to accelerated CO 2 fixation, ChlF tends to decrease from M2 peak to T (steady state) ChlF level. However, time at which M peaks are reached within ChlF transients, seems to be highly dependent on a lichen species (see Conti et al 2014, Usnea antarctica, Stereocaulon vesuvianum), actual extent of photoinhibition (Barták et al 2012) and acclimation to particular experi-mental temperature. In our study, U. antarctica and P. muscigena showed M1 and M2 peaks only at 10 and 5°C while M1 was missing at the temperature above 10°C.…”

Production of UV-B screens and changes in photosynthetic efficiency in Antarctic Nostoc commune colonies and a lichen Xanthoria elegans depend on a dose and duration of UV-B stress

“…In some Antarctic lichens, P might be higher than M as shown e.g. for Usnea antarctica (Barták et al 2012). Those Kautsky kinetics recorded for N. commune were rather flat (Fig.…”