Water Relations and Composition of Wheat Ears Grown in Liquid Culture: Effect of Carbon and Nitrogen

Detached wheat ears were grown, under lighted controlled conditions, in liquid culture media containing different concentrations of sucrose and amino acid. Higher levels of sucrose in the culture medium resulted in decreased transpiration, with large accumulations of soluble sugar in the bracts. The sugar accumulations led to decreased total and osmotic potentials of the bracts, but turgor was maintained or increased. The concentration of sucrose or nitrogen in the culture medium had no significant effect on the water or osmotic potentials of the grain. Soluble sugar concentrations in the grain were not affected by increasing the sucrose concentration in the culture medium. Increasing the nitrogen level in the culture medium led to increased concentrations of total nitrogen and non- protein nitrogen in the grain. Higher protein levels in the grain resulted in increased water content but no significant changes in the water potential of the grain. The grain was the strongest nitrogen sink within the ear and, within the grain, starch and protein synthesis were independent of each other. Proline accumulated in the bracts and to a lesser extent in the rachis in response to the accumulation of soluble sugars and nitrogen rather than to the low osmotic or total water potentials. Little proline accumulated in the grain and this was presumed to be due to translocation from other parts of the ear rather than to in situ synthesis.