Characterization of Spring Wheat Genotypes Differing in Drought-Induced Abscisic Acid Accumulation: II. LEAF WATER RELATIONS

Aspects of the water relations of spring wheat (Triticum aestivum L.) are described for cultivars Highbury (low ABA) and TW269/9 (high ABA), and low and high ABA accumulating F6 selections derived from a cross between them. In a pot experiment, pressure—volume (P—V) curves were constructed for main stem leaf four (MSL4) of well-watered plants of Highbury and TW269/9. Estimates of solute potential (Ψs) from these curves were similar for the two cultivars, but varied with the time of sampling and the time allowed for hydration in dim light. In a field experiment with four low and four high ABA F6 lines, P—V curves for flag leaves from both droughted and irrigated plants gave Ψs at both zero turgor (Ψp) and zero water potential (ΨL) which differed with degree of stress, sampling time and genotype. Ψs was strongly dependent on the initial ΨL of the leaf and was reduced on average by c. 0.4 MPa per MPa decline in initial ΨL. Ψs was lower (more negative) by c. 0.1 MPa in the afternoon than in the morning. Overall, Ψs was also 0.1 MPa lower in low ABA lines than in high ABA lines. In another field experiment, flag leaves of five low and five high ABA F6 lines were sampled over a 4 week period from droughted plots and ΨL and Ψs measured (the latter by osmometry with expressed sap). For these leaves Ψs at zero Ψp or zero ΨL was consistently lower by 0.3—0.5 MPa than estimates of Ψs from the P—V curves with flag leaves. However, Ψs data for the low ABA lines were again lower (by c. 0.1 MPa) than those for high ABA lines. The consequences of these differences in Ψs are discussed in relation to the stimulation of ABA accumulation in low and high ABA selections.