Gibberellin A3and Abscisic Acid Cause the Reorientation of Cortical Microtubules in Epicotyl Cells of the Decapitated Dwarf Pea

摘要

To determine whether or not the changes in the orientation of microtubules (MTs) that are induced by GA3and ABA result from changes in the rate of epicotyl elongation caused by these hormones, we examined the effects of GA3and ABA on the orientation of MTs in epidermal cells of decapitated epicotyls of the dwarf pea (Pisum sativumcv. Little Marvel), in which neither GA3nor ABA causes changes in the rate of epicotyl elongation.Cuttings taken from GA3-pretreated seedlings were decapitated and treated with ABA. ABA eliminated the GA3-induced predominance of transverse MTs and treatment with ABA resulted in a predominance of longitudinal MTs in the decapitated cuttings. However, ABA did not reduce the rate of epicotyl elongation in these samples. Cuttings taken from ABA-pretreated seedlings were decapitated and treated with GA3. GA3caused the orientation of MTs to change from longitudinal to transverse in the decapitated cuttings. However, GA3had no promotive effect on elongation of these epicotyls.The results indicate that both ABA and GA3have the ability to change the orientation of MTs by mechanisms that do not involve changes in the rate of cell elongation.