The Effect of Flowering on Stomatal Response to Water Stress in Pearl Millet (Pennisetum americanum[L.] Leeke)

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 g_L and stage of panicle development, it is concluded that the tendency of stomata to remain open despite water stress and loss of bulk leaf ψ_P is related to the presence of an emerged panicle. Hypotheses which account for this effect are discussed.