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Osmotic Adjustment and Solute Accumulation in Two Wheat Genotypes Differing in Drought Resistance¹

Field observations have indicated that the winter wheat (Triticum aestivum L.) cv. TAM W-101 is relatively drought resistant compared with the cv. Sturdy. In a growth chamber experiment, osmotic adjustment and various solutes potentially involved in osmotic adjustment were measured in leaves of TAM W-101 and Sturdy. Plants were grown in sand culture for 28 days at 20°C with 16 h light per day (=600 µmol m^-2 s^-1). Stress treatments were then imposed by limiting water in pots for 14 days, after which water relations were determined with pressure-volume curves on leaves of stressed plants following overnight hydration (prestressed), and on hydrated unstresssed plant leaves. Leaf solutes measured were total amino acids, proline, free sugars, and K. Prestressed leaves of both cultivars had significantly lower solute potential at full turgor (^f_s) and zero turgor (^o_s) than unstressed leaves, indicating osmotic adjustment. But prestressed TAM W-101 apparently adjusted more, with significantly lower values for ^f_s (–1.61 MPa) and ^o_s (–2.44 MPa) compared to prestressed Sturdy (–1.40 and –1.98 MPa, respectively). The relative reduction of dry matter produced in prestressed TAM W-101 plants did not, however, differ from prestressed Sturdy plants. Water use efficiency (WUE, mg total dry matter/g H₂O lost per pot) was significantly lower in TAM W-101 (2.27) than in Sturdy (2.55) and in prestressed (1.81) than unstressed (2.40) leaves. Tissue elasticity was also lower in TAM W-101 than Sturdy and lower in prestressed than unstressed leaves. Nonreducing sugars increased from 15 g/kg dry wt in unstressed to 39 g/kg dry wt in prestressed (1.4%) leaves, but reducing sugars did not differ among treatments. Only amino acids, including proline, were greater in prestressed TAM W-101 than Sturdy leaves. But calculated as ideal osmotica, amino acid concentrations were too low to explain the difference in ^f_s between prestressed cultivars. As the adaptive significance of the cultivar differences in osmotic adjustment, WUE, and tissue elasticity are clarified, selection for these factors to improve wheat drought resistance may be possible.

Key Words: Triticum aestivum L. • Water deficits • Proline • Amino acids • Carbohydrates • Water potential • Water use efficiency

² Assistant professors and professor of Agronomy, respectively. Dep. Agronomy, Oklahoma State Univ., Stillwater, OK 74078.

Received for publication August 26, 1983.

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