Studies on the Physiology of Light Action. Iv. Light Enhancement of Auxin-induced Growth in Green Peas.

In the first paper of this series (3), it was demonstrated that the auxininduced growth in length of sub-apical sections of etiolated pea stems -is greatly inhibited by light. This light-growth inhibition was subsequently (1, 2) interpreted in terms of a riboflavin-sensitized photoinactivation of indoleacetic acid (IAA). Such an interpretation derives support from the fact that light, concurrent with its inhibition of growth, increases the rate of disappearance of IAA from the external medium. In the course of similar experiments with stem sections of light-grown peas, we noticed that light enhances, rather than inhibits, the auxin-induced growth. This response was unexpected and of such great magnitude that it was considered desirable to investigate it more fully. The present paper describes the phenomenon in some detail and presents an explanation of it which seems consistent with all the facts at our disposal. The simple section growth test herein described may, incidentally, be of some use to those interested in utilizing green tissues for auxin or herbicide studies.