Gibberellin-induced elongation and osmoregulation in internodes of floating rice

Abstract

Internodal elongation in floating rice (Oryza sativa L. cv. Habiganj Aman II) is known to be enhanced by treatment with ethylene or gibberellic acid (GA 3 ) at high relative humidity (RH). However, ethylene-induced internodal elongation is inhibited at low RH, while GA 3 -induced internodal elongation is hardly affected by humidity. We examined the possible involvement of osmoregulation in the stimulation by GA 3 of the elongation of internodes at low RH. Submergence and treatment with ethylene or GA 3 at 100% RH increased the osmotic potential in internodes of excised stem segments, while GA 3 at 20% RH maintained the osmotic potential at a low level. In internodes of stem segments that had been treated with GA 3 at 20% RH, the activity of invertase and the level of soluble sugars were almost 2- and 1.5-fold higher, respectively, than those in internodes that had been treated with GA 3 at 100% RH. These results indicate that one of the possible mechanisms by which GA 3 promotes elongation of internodes at low RH involves the osmoregulation that is achieved by promotion of the synthesis of invertase.