Gibberellins and Light Inhibition of Stem Growth in Peas

Light-induced inhibition of stem growth is a common phenomenon in plants. Particularly well investigated is the case of peas, Pisum sativum, mainly thanks to the work of Lockhart. Lockhart showed that growth of Alaska peas, a tall variety, was retarded when plants were transferred from darkness to low-intensity light but that, after a period of inhibition, the plants resumed growth at a rate equal to those grown continuously in the dark (5, 7). Applied gibberellic acid reversed the inhibition caused by light. The effect of irradiation on the growth of dwarf peas is even more drastic. Dwarf peas grow like, or nearly like, the tall types in darkness (1) but when they are exposed to light, stem elongation is strongly reduced (1, 5, 6) and the plants do not regain their original growth rate but stay dwarfed as long as kept in the light. Again the effect of illumination can be overcome by gibberellic-acid treatment. Light inhibition in dwarf peas is mediated by the phytochrome system, red light being most effective in causing suppression of growth and far red negating the effect of a previous irradiation with red light (5, 6). Lockhart postulated that light interferes with the metabolism of endogenous gibberellins in plants. Our experiments were aimed at finding whether lightand dark-grown dwarf peas exhibit quantitative and qualitative differences in their gibberellin content and/or in their responses to applied gibberellins.