Gibberellins and Light Inhibition of Stem Growth in Peas

Abstract

Light-induced inhibition of stem growth is a com-mon phenomenon in plants. Particularly well investi-gated 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 re-tarded when plants were transferred from darkness to low-intensity light but that, after a period of inhibi-tion, 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 re-gain their original growth rate but stay dwarfed as long as kept in the light. Again the effect of illumina-tion 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 light-and dark-grown dwarf peas exhibit quantitative and quali-tative differences in their gibberellin content and/or in their responses to applied gibberellins. Materials and Methods Bioassays. The main bioassay for pure gibberel-lins and for gibberellin-like materials in extracts was a dwarf-pea assay developed in this laboratory by E. Reinhard (4). Alaska peas and a dwarf corn mu-tant, d5, served as complementary assay plants. Dwarf peas, var. Progress No. 9 (Asgrow, New Haven, Connecticut), were soaked for 24 hours at room temperature in vermiculate and kept in darkness at 230. On the third day after sowing seedlings were selected for uniformity and transferred to plastic boxes containing half-strength Hoagland solution. Plants were measured and selected again on the fourth day and then treated with test solutions. Gibberellins 1 Received Sept. 3, 1963.