The Interaction of Auxin and Light in the Growth Responses of Plants

Abstract

The information presented above suggests that many heretofore unrelated processes which are affected by both light and auxin, including red light induced growth of the Avena coleoptile, the photoperiodic response, leaf expansion, and seed germination, may all have their basis in a common mechanism. All of these processes have approximately the same action spectra with effective peaks at ca. 660O, all are freely reversed by infra-red light, and all appear to be auxin-dependent. It has been shown that in the case of the Avena coleoptile, red light appears to exert its effect through the generation of an auxin-receptive entity, E, within the plant and that infra-red light acts to decompose the active complex ES into an auxin-non-receptive entity. In the coleoptile these processes also proceed thermally although at reduced rates. This is particularly true of the infra-red mediated decomposition of ES. The present paper calls attention to the fact that a concept of the cyclic interconversion of auxin-non-receptive precursor, auxin receptor, and receptor-auxin complex by light and dark can be applied without violence to the interpretation of these varied plant responses. The concept presented, that of the photo-cycle, at once suggests a variety of experimental approaches which may be used to further test its validity in each individual instance.