Physiological and biochemical mechanisms involved in the response to abscisic acid in maize coleoptiles

The role of abscisic acid (ABA) in controlling growth and development has been studied in maize (Zea mays L.) coleoptile segments. Application of ABA reduces the elongation rate by about 50% and affects ion fluxes, In particular, proton extrusion is decreased while potassium efflux is greatly enhanced, Apparently, ABA does not seem to influence calcium influx from the apoplast into the cytosol, but more likely it influences its efflux. Alteration of cytosolic calcium concentration may also be obtained by increasing its release from internal stores, This possibility might be sustained by the increased hydrolysis of phosphatidylinositol upon ABA application, Change in the balance of ion fluxes should result from regulation of transport mechanisms at the membrane level and should produce changes in the transmembrane electrical potential, The H+-ATPase and the ATP-dependent calcium transport activities are both influenced by the treatment with ABA, -55% and -40%, respectively. Under these conditions [Ca2+](cyt) and pH(cyt) can be modified and, as a consequence of their regulation, they may play an important role in mediating the physiological and biochemical effects of ABA, acting as second intracellular messengers.