Abstract
Lichens are photoautotrophical symbionts containing algae and can live even in the drought environment. It has been suggested that lichens convert absorbed light energy into thermal energy efficiently in the drought conditions, although the mechanism is still unclear. We measured the lifetime of fluorescence of a lichen, Pertusaria sp. using pico-second time resolved spectrophotometer, and analyzed the process of energy conversion. We obtained following results. (1) The fluorescence of photosystem II decayed much faster in the dried cells. (2) Excitation energy transfer within photosystem II was still observed in the dried cells. (3) The lifetime of photosystem II was increased within 1 min after water-absorption. (4) The blue shift and the shortening of the lifetime were also observed in photosystem I upon dehydration. Similar features were observed in other lichens. We discuss this energy dissipation mechanism from these results.
