The end-of-day far-red irradiation increases gibberellin A(1) content in cowpea (Vigna sinensis) epicotyls by reducing its inactivation
2000
Martínez-García, Jaime F. | Santes, C. M. | García-Martínez, José-Luis
It has been shown previously that gibberellins (GAs) mediate the phytochrome (Phy) control of cowpea (Vigna sinensis L,) epicotyl elongation induced by end-of-day (EOD)-far-red light (FR), In the present work, the EOD-FR effect on GA metabolism and GA levels in cowpea has been investigated, GA(1), GA(8), GA(19) and GA(20) were identified in epicotyls, and GA(1), GA(19), GA(20) and GA(29)-catabolite in leaves of 6-day-old cowpea seedlings, The content of GA(1) in the epicotyl paralleled the decrease of its growth rate, supporting the hypothesis that this is the GA bioactive in controlling cowpea epicotyl elongation. FR enhanced both the amount of [H-3]GA(1) in the epicotyl produced from applied [H-3]GA(20), and that of applied [H-3]GA(1) that remained unmetabolized in epicotyl explants, suggesting that Phy mag regulate the inactivation of GA(1). In agreement with this effect of light on GA(1) metabolism, the contents of GA(1) in the epicotyl remained higher in FR-treated than in R-treated explants, Moreover, in intact seedlings EOD-FR treatment increased both epicotyl elongation and GA(1) content in the responsive epicotyl, whereas it was not altered in the leaves, These results show, for the first time, that photostable Phys modulate the stem elongation in light-grown plants by locally controlling the GA(1) levels through regulation of its inactivation.
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