When there is too much light.

A great deal of importance has happened in research investigating photosynthetic response to environmental stress in the 25 years since the last anniversary issue of Plant Physiology. However, from my perspective, the importance of one set of discoveries stands out from the others for its far reaching influence on how we think about the photosynthetic response to a wide range on environmentally imposed limitations. As little as 15 years ago it was generally held that the success of plants in their environment was dictated by strategies that maximized the rate of photosynthesis. Further, maximum photosynthetic capacity was thought to be largely a static characteristic of individual leaves that was established during development. This view has now given way to the recognition that the regulation of photosynthesis in response to the environment is highly dynamic and dominated by a photoprotective process, the nonphotosynthetic thermal dissipation of absorbed light (4, 10, 14), which was entirely unknown at the time of Plant Physiology’s 50th Anniversary. This brief overview describes what is currently understood about this centrally important photoprotective process and highlights areas of current inquiry that may presage a detailed mechanistic understanding in the near future.