Photoprotective mechanisms activated in Antarctic moss <i>Chorisodontium aciphyllum</i> during desiccation

We investigated the relationship between relative water content (RWC) of Antarctic moss Chorisodontium aciphyllum and several chlorophyll fluorescence parameters evaluating primary photochemical processes of photosynthesis. During the gradual dehydration of Ch. aciphyllum from fully wet (RWC=100%) to dry (RWC=0%) state, progression of NPQ (non-photochemical quenching) induction curves were recorded; the maximum NPQ (NPQmax) attained at the end of illumination period (10 min.), and NPQ relaxation in dark were all analysed. Induction curves of photosynthetic electron transport rate (ETR) were also evaluated, as well as two parameters, ETRmax and initial slop, were derived from the curve: (1) ETRmax; (2) initial slope (a parameter). The two parameters were related to the degree of desiccation (RWC decdlining from 100 to 0%). It was found that NPQ induction curves and the parameters derived from them were sensitive to dehydration and may be used as markers for dehydration-induced changes in photosystem II functioning of desiccating Ch. aciphyllum. The activation of non-photochemical quenching during desiccatin and the underlying mechanisms are discussed.