Effects of Water Deficit on Endosperm Starch Granules and on Grain Physiology of Wheat and Barley.

Abstract

Wheat (cv. Sun 9E) and barley (cv. Clipper) plants were subjected to water deficit after anthesis. In both species grain dry matter accumulation was initially unaffected by water deficit but terminated earlier in stressed plants than in controls. Water deficit did not affect endosperm cell number. In water stressed wheat plants the number of B-type starch granules per endosperm and the size of the largest A-type granules were significantly less than in control plants but A-type granule number was unaffected. Water potentials of wheat flag leaves and bracts were reduced by water deficit but this treatment did not affect grain water potential or osmotic potential during the first 29 days after anthesis. During these 29 days, neither grain nor bract water potential of barley was affected by stress and the water potential of bracts was relatively low even in control plants. Maturing grains eventually lost water and endosperm volume declined. This water loss occurred earlier in stressed plants. Stress significantly reduced the amount of sucrose per wheat grain but not the amount of sucrose per unit of grain dry matter or water content. In barley grains, stress did not reduce the relative or absolute sucrose contents. It was considered unlikely that the earlier cessation of grain growth on stressed plants was caused by insufficient assimilate. Although protein as a proportion of grain dry weight was higher in stressed plants than in controls, protein and amino acid content per grain were unaffected by water deficit.