Abstract
Some bryophytes are known to have high desiccation tolerance. In order to find out the mechanism of the tolerance, we have investigated changes in various photosynthetic activities caused by dehydration using bryophytes grown under different water environments. We found that PSII fluorescence is quenched and the PSII reaction center (PSIIRC) activity is lost by dehydration, which seems to be important to protect PSII under dry conditions. However, even in desiccation-tolerant species, partial dehydration by sorbitol treatments give the state where the photosynthetic activity was lost but the PSIIRC activity was remaining. We investigated the effect of high light at this state, and found that PSIIRC was practically deactivated by nonphotochemical quenching (NPQ), which was not recovered by dark incubation. This NPQ was found not to be caused by the xanthophyll cycle and to be very important for desiccation tolerance. Here we will report on details of this NPQ.