Plant Photobiology in the Last Half-Century

The absorption of light energy not only nourishes the plant through photosynthetic phosphorylation and concomitant carbon dioxide fixation, but it also determines the nature and the direction of plant growth. This review will summarize the major advances in the physiology of both of the latter processes over the last half-century. Because of severe limitations of space, only a few key concepts can be mentioned, let alone emphasized, and some fields, like algal phototaxis, must be omitted entirely. Although there was certainly provocative earlier work by Klebs and others (100), our present understanding of the control of form by light, or photomorphogenesis, began with the clear enunciation of the principles of photoperiodism by Garner and Allard (55, 56) a little more than 50 years ago. Photomorphogenetic transformations are mediated mainly by the longer wavelengths of the visible spectrum (105), and are these days attributed mainly or exclusively to absorption by phytochrome. The development of the phytochrome concept by