PHOTOMORPHOGENIC PROCESSES IN THE AGRICULTURAL ENVIRONMENT

We review recent advances in our understanding of how photomorphogenic mechanisms influence processes of significance for agriculture, including weed seed germination. acclimation to solar UV-B radiation, and plant interactions in canopies. It has been demonstrated recently that seeds of some weed species acquire the ability to germinate in response to very low photon fluences during burial. Short sunlight pulses perceived by seeds during tillage appear to be important signals of soil disturbance. Regarding UV-B acclimation there is increasing evidence for the involvement of a specific UV-B photoreceptor in pigmentation and morphological responses to UV-B. The protective role played by UV-B-induced flavonoids has been experimentally demonstrated. Concerning plant interactions in canopies it has been shown that, by perceiving light signals through phytochrome and blue-UV-A photoreceptors, plants obtain information about the characteristics of the surrounding vegetation well before their resources are reduced as a consequence of neighbors' activities. There appears to be a large potential for improving cropping systems by manipulating the light environment or by changing the photomorphogenic behavior of crop plants. However, relatively little is known about how the expression and agronomic significance of photomorphogenic responses are influenced by other factors of the plant's environment.