METABOLISM AND TRANSLOCATION OF GIBBERELLINS IN SEEDLINGS OF PHARBITIS-NIL .1. EFFECT OF PHOTOPERIOD ON STEM ELONGATION AND ENDOGENOUS GIBBERELLINS IN COTYLEDONS AND THEIR PHLOEM EXUDATES

Gibberellin A(1) (GA(1)), GA(19), and GA(20), in phloem exudates and cotyledons of seedlings of Pharbitis nil cv. Violet, grown under different photoperiodic conditions, were qualitatively and semi-quantitatively analyzed by a combination of high performance-liquid chromatography (HPLC) and radioimmunoassays (RIA). The levels of GA(19) and GA(20) were higher in cotyledons from plants grown under dark treatment (DT) conditons of 16 h-light/8 h-dark for 6 days followed by 8 h-light/16 h-dark for 3 days than in those grown under continuous light (CL) for 9 days. This relationship was also observed for the GAs in phloem exudates, although the levels were much lower than in the cotyledons. When GAs were applied to the cotyledons, elongation of the epicotyl was promoted more by GA(20) than by GA(1) or GA(19), especially under the CL treatment. The relative effect of GA(1) and GA(20) on the epicotyl elongation was reversed when these GAs were applied to epicotyls pre-treated with prohexadione, an inhibitor of 2-oxoglutarate-dependent dioxygenases.