Leaf Abscisic Acid Content and Recovery from Water Stress in Pearl Millet (Pennisetum americanum[L.] Leeke)1

Abstract

Water potential (ψ) and abscisic acid (ABA) content were measured in leaves of drought-stressed, field-grown plants of pearl millet (Pennisetum americanum [L.] Leeke) during rehydration, initiated either in response to a diurnal night-time reduction in evaporative demand, or to irrigation. Overnight rehydration, manifested as a substantial increase in ψ, was not accompanied by any reduction in ABA levels. In contrast, an increase in ψ following irrigation resulted in an appreciable reduction in ABA content. Such reduction was, initially, only partial when field plants were rewatered at dusk, but was rapid and complete within 3 h when irrigation was applied mid-afternoon. The possibility that light or temperature changes might have prevented loss of ABA during night-time rehydration was investigated in pot experiments. At similar air temperatures, young pot-grown plants rehydrated more rapidly, and ABA levels fell more quickly, in darkness than in light. The onset of rehydration and loss of ABA in darkness were delayed by low (20 °C) compared with high (28 °C) temperature, though after an initial lag, rates of both processes at 20 °C were similar to rates at 28 °C. Neither light nor temperature affected the relationship between ABA content and *.