Solute Accumulation in the Apex and Leaves of Wheat During Water Stress

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Abstract
Accumulation of several low-molecular-weight solutes was measured in the developing floral apex, in an enclosed, elongating leaf, and in an expanded leaf of wheat plants during a 13-day period of water stress. In the apices and enclosed leaves, osmotic potential fell from - 1.2 to -4.0 MPa. The main contribution to the decline in osmotic potential during the first 3 days of stress was from an increase in the content of ethanol-soluble carbohydrate. Later, increases in the concentrations of both carbohydrates and amino acids made major contributions. Of the amino acids, the largest increases were in asparagine and proline. The enclosed tissues lost little water, although the water- to-dry matter ratio declined as a result of imported solutes. The ethanol-insoluble nitrogen content of apices remained high, and growth of apices and enclosed leaves recommenced when plants were watered after 13 days. In exposed leaves, increases in carbohydrate and amino acid contents were comparatively small, and the content of ethanol-insoluble nitrogen decreased by 50%. These leaves dehydrated within 6 days, and failed to recover when the plants were rewatered.