Delay in the Response of Stomata to Abscisic Acid in CO2-free Air

Abstract

Abscisic acid ( 10~5 M) was fed via their petioles to leaves detached from well watered plants of Xanthium strumarium, while the intercellular spaces were flushed with air of known CO2 content. A closing response to ABA occurred in the presence or absence of CO2, and the stomata responded to CO2 whether or not ABA was supplied to the leaves. A factorial experiment revealed no interaction between CO 2 and ABA, and suggested that their effect on the rate of closure was purely additive. The only evidence of interdependence between the two com pounds was a delay in the response to ABA in C02-free air, which was more marked in a high light intensity. A hypothesis which is consistent with the data is that ABA induces stomatal closure by interfering with the energy supply required for the active transport processes on which guard cell turgor depends. The inhibitory action of ABA takes longer in CO2-free air because, in the absence of CO2 fixation, energy is available from chloroplasts as well as mitochondria.