Solute Accumulation and Growth in Plants of Pearl Millet (Pennisetum americanum[L.] Leeke) Exposed to Abscisic Acid or Water Stress

Henson, I. E. 1985. Solute accumulation and growth in plants of pearl millet (Pennisetum americanum [L.] Leeke) exposed to abscisic acid or water stress.—J. exp. Bot. 36: 1889–1899. Experiments were conducted to investigate whether abscisic acid (ABA) elicits the accumulation of solutes and lowering of osmotic (solute) potential (Ψ2) which occurs in leaves of pearl millet (Pennisetum americanum [L.] Leeke) exposed to water stress. When (±)−ABA was injected into the base of the shoot of 15–d–old plants, Ψ2 of the fifth leaf was reduced significantly below controls 27–72 h after treatment. The reductions, however, were small (< 0.10 MPa) and were accompanied by a significant inhibition of shoot growth. In contrast, no significant reduction in Ψ2 or in growth occurred when the hormone was introduced directly into leaf five via its mid–rib. ABA concentrations in leaf five were high shortly after direct injection, but declined to control levels within 48 h. Injecting ABA into the shoot base resulted in lower leaf five ABA concentrations. Hence, the ABA concentration in the leaf was not the most critical factor for its effect on Ψ2. ABA also reduced Ψ2 of shoots when applied to seedlings 48 h or 72 h after sowing via the roots. As with older plants, the effects of ABA on Ψ2 were small (≅ 0–2 MPa) and were accompanied by inhibition of shoot growth. A water stress treatment and an ABA treatment were compared. Although both treatments resulted in a similar degree of growth inhibition, the stress treatment was much more effective than was ABA in reducing Ψ2.