Gibberellins and phytochrome regulation of stem elongation in pea

Abstract

In garden pea (Pisum sativum L.) neither etiolation nor the phytochrome B (phyB)-response mutation lv substantially alters the level of the major active endogenous gibberellin, GA1 in the apical portion of young seedlings. The phyB-controlled responses to continuous red light and end-of-day far-red light are retained even in a GA-overproducing mutant (sln). Comparison of the effects of the lv mutation and GA1 application on seedling development shows important differences in rate of node development, cell extension and division, and leaf development. These results suggest that in pea the control of stem elongation by light in general and phyB in particular is not mediated by changes in GA1 content. Instead, the increased elongation of dark-grown and lv plants appears to result from increased responsiveness of the plant to its endogenous levels of GA1. Three GA1-deficient mutants, na, ls and le have been used to investigate these changes in responsiveness, and study of these and the double mutants na lv, ls lv and le lv has demonstrated that the relative magnitude of the change in responsiveness is dependent on GA1 level. The difference in pleiotropic effects of GA1 application and the lv mutation suggest that light and GA1 interact late in their respective transduction pathways. A model for the relationship between light, GA1 level and elongation in pea is presented and discussed.