The Responses of Stomata to Abscisic Acid and Temperature are Interrelated.

The usual response of stomata to abscisic acid (ABA) is a promotion of closure or an inhibition of opening. There are, however, a few reports that at low temperatures the stomata of chill-sensitive species show a reversal of this normal effect, i.e. ABA causes stomatal opening. We have reinvestigated the interactions between ABA and temperature on stomatal movements in detached epidermis of two species which are not chill sensitive, Bellis perennis and Cardamine pratensis, and, for comparison, the subtropical plant Commelina communis. A major effect of low temperatures was to reduce the stomatal response to ABA. This applied to all species (i.e. whether chill sensitive or not), suggesting that it is a widespread occurrence which may be of physiological and ecological significance. It was also demonstrated that, above approximately 15 degrees C, the magnitude of the stomatal response to ABA tends to increase with temperature and hence temperature-induced stomatal opening is moderated by the presence of ABA. These data suggest that some reinterpretation is required of the role of ABA during periods of water shortage. We propose that an important regulatory role of the hormone is to limit stomatal opening at periods when the evapotranspirational demand is greatest at higher temperatures, but to allow opening when temperatures are low and thereby facilitate the uptake of carbon dioxide