Abstract
Lichens are photoautotrophical symbionts containing algae. It has been suggested that lichens convert absorbed light energy into thermal energy under the drought conditions. We investigated 20 pieces of lichens to clarify the excitation energy transfer and electron transfer processes under the drought conditions. We classified lichens into 3 groups based on the drying-responses of fluorescence spectra at 77 K. Fluorescence lifetime analysis further indicated that the light energy absorbed by photosystem II is rapidly quenched in the two groups in the dry conditions. The remaining one group was shown to protect photosystem II by decreasing the antenna size in the dry conditions. The delayed fluorescence emitted from photosystem II at 50-100 ns indicated the electron transfer from P680 to pheophytin is still active. We also measured the delayed fluorescence in the millisecond domain and the thermoluminescence in the dry conditions. We will discuss the energy dissipation mechanisms from these results.
