Stimulation of Pisum sativum epicotyl elongation by gibberellin and auxin. – Different effects of two hormones on osmoregulation and cell walls

Abstract

The possible involvement of auxin in the action of gibberellin in stimulating cell elongation was examined by comparing the effects of gibberellic acid (GA) and IAA on the growth, osmoregulation and cell wall properties of the Alaska pea (Pisum sativum L. cv. Alaska) subhook. Both GA and IAA stimulated cell elongation in the subhook region of derooted cuttings. Cotyledon excision decreased the stimulating effect of GA on the growth of the subhook region, but did not affect that of IAA. As the subhook region elongated, the osmotic potential of the cell sap and the total amount of osmotic solutes increased. Cotyledon excision accelerated the increase in the osmotic potential and suppressed the accumulation of osmotic solutes. In cuttings with cotyledons. GA partly counteracted the increase in the osmotic potential and substantially promoted the accumulation of osmotic solutes. On the other hand, in cuttings without cotyledons. GA did not affect the change in the osmotic potential although it slightly promoted the accumulation of osmotic solutes. IAA accelerated the increase in the osmotic potential, but did not affect the accumulation of osmotic solutes. IAA enhanced the extensibility of the cell wall, while GA did not affect it. These results suggest that at least in the Alaksa pea subhook region. GA does not stimulate cell elongation by affecting the level of auxin.