Modification of the CO2Responses of Maize Stomata by Abscisic Acid and by Naturally-Occurring and Synthetic Cytokinins

Abstract

Fragments of maize leaves were incubated at controlled temperature and irradiance either on distilled water or on one of three concentrations of cytokinin (10', 102 and 103 mol m~3). The effects of zeatin or kinetin on stomatal aperture were determined by stripping abaxial epidermis from the fragments after incubation and immediately measuring stomatal apertures under the microscope. At each cytokinin concentration leaf pieces were incubated at 5 or 350 //mol mol1 CO, with or without ABA ( 10 1 mol m3). At 5-0 //mol mol' C02 increasing the concentrations of zeatin had a negligible effect upon stomatal aperture. When air containing 350 //mol mol1 CO, was bubbled through the incubation solutions, apertures of stomata incubated on water were more than halved. Increasing cytokinin concentrations reduced the effect of CO, on stomata and incubation on 101 mol m3 zeatin completely removed any C02 response. The addition of ABA restored the effect of C02, even at the highest cytokinin concentration.