Abstract
Stomata on upper leaves of drought-stressed pearl millet (Pennisetum americanum [L.] Leeke) crops were more open in flowering (F) than in pre-flowering (PF) plants. This was not due to differences in leaf water potential (ψ). Stomata of PF plants closed when ψ fell to about −1.7 MPa, while on F plants stomata closed only when ψ approached −2.3 MPa. Osmotic adjustment did not account for these differences as relations between turgor potential (P) and Ω were similar in F and PF plants. While stomata of PF plants closed as W became zero, in F plants stomata remained open even after bulk leaf turgor was lost. Differences between F and PF plants were not explained by differences in age of leaves sampled. However, leaves of water-stressed PF plants had higher levels of abscisic acid (ABA) than leaves of F plants, despite similarities in water status. From these results and from relationships between gL and stage of panicle development, it is concluded that the tendency of stomata to remain open despite water stress and loss of bulk leaf ψP is related to the presence of an emerged panicle. Hypotheses which account for this effect are discussed.