Abstract
Stomatal responses to water stress and to applied (±)-abscisic acid (ABA) were examined in genotypes of pearl millet (Pennisetum americanum (L.) Leeke) known to differ in amounts of endogenous ABA accumulating during drought. In both a pot and a field experiment, Serere 39, a genotype with a high capacity to accumulate ABA, showed a higher stomatal sensitivity to water stress than did the ‘low’ ABA accumulator, BJ 104. In the field experiment, a third genotype, B282, accumulating least amounts of ABA, also had the lowest stomatal sensitivity to water stress. There were no significant differences between these genotypes in stomatal response to applied (±)-ABA, or in the relationships between leaf conductance and levels of endogenous ABA. It is concluded that the differences in accumulation of endogenous ABA by these genotypes of pearl millet are of functional significance, and that endogenous ABA generated during a water stress which develops over days or weeks mediates stomatal responses to such stress.