An Association between Flowering and Reduced Stomatal Sensitivity to Water Stress in Pearl Millet [Pennisetum americanum (L.) Leeke]

Stomatal sensitivity to water stress was investigated in pearlmillet Pennisetum americanum (L.) Leeke] in relation to stageof plant development, leaf water status and ABA content by samplingplants at midday. For the same leaf water potential (), droughtedplants with emerged panicles were found to have a greater leafconductance (g_L), indicative of greater stomatal opening, thanplants sampled prior to panicle emergence. The difference betweensuch flowering (F) and non-flowering (NF) plants in at stomatalclosure was estimated to be at least 0.6 MPa. This differencewas considered unlikely to be the result of differential bulkleaf osmotic adjustment, and for most samples from both F andNF plants, bulk leaf turgor potential (_p) was estimated to bezero. Stomatal closure in NF plants was associated in two genotypes(BJ 104 and line 112) with higher leaf ABA levels. Differencesin ABA levels between F and NF plants were, however, smalleror absent in genotypes Serere 39 and B282. These genotypes wereat lower than BJ 104 and line 112 when sampled and showed smallerdifferences between F and NF plants in conductance. Lower ABA levels in F plants are ascribed either to effectsof leaf ageing or to effects of flowering on ABA content ofthe leaf. Significant differences in g_L in the absence of differencesin ABA content are taken to imply changes in stomatal sensitivityto the hormone or in its access to the stomatal complex. Pennisetum americanum (L.) Leeke, pearl millet, flowering, stomata, water stress, abscisic acid