Research on chilling-induced damage as a kind of photoinhibition

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Green plants undertake photosynthesis. It provides us with most of our living energy and most of our raw materials. All the living organisms on the earth, plants, animals and bacteria, depend on the energy in the sunlight. Because of its importance, the research in photosynthesis has long history, and almost all the structural proteins involved in the photosynthetic electron transport chain have been identified and their genes sequenced by now. Although we have really good static image of photosynthetic apparatus, we do not know much about the dynamic aspects of photosynthesis in ever changing environments. For example, decrease of the photosynthetic activity is observed after exposure of leaves to chilling temperatures. Chilling-induced damage to photosynthesis has three characteristics : existence of threshold temperature, irreversibility, and development of visible symptoms after worming up. Although the cause of these characteristics was enigma for more than 20 years, we found that these characteristics could be explained by the photoinhibition of Photosystem I. Furthermore, we isolated several mutants that showed no specific phenotype under usual growth condition, but peculiar fluorescence kinetics after chilling treatment. The characterization of these mutants must be very useful to understand the molecular mechanisms underlining the temperature response of plants.