Abstract
Lichen is a symbiotic organism of a fungi as a host and an alga or (and) a cyanobacterium as a guest. Lichen shows high tolerance to the strong light under drought condition. Recent studies have shown that lichen has a specific mechanism to effectively convert excessive light energy into heat under drought condition. We have performed the time-resolved fluorimetry of lichens at cryogenic temperature to identify the molecular location where this mechanism functions. The study clarified that the quenching of the excitation energy occurs in photosystem II. The lichen containing Trebouxia as a symbiotic alga has a fluorescence component at 740 nm, which seems to contribute to the energy dissipation. In the present study, we report the results in a green alga Trebouxia isolated from a lichen R. yasudae obtained by time-resolved fluorimetry in cryogenic temperature. The isolated Trebouxia showed no rapid energy dissipation upon desiccation as in lichen. However, the ability of rapid energy dissipation was reproduced by drying with a sugar. The results suggest the essential role of the sugar for the drought-tolerance of Trebouxia.
