Grain-Filling in Wheat Plants Shaded for Brief Periods After Anthesis

Abstract

Plants of wheat (grown in a controlled environment) were subjected to brief (5-10 days) periods of shading just after the ears showed the first signs of anthesis, and afterwards were grown to maturity in full illumination. Shading resulted in smaller grains, slower rates of accumulation of dry matter in the grains, and lower final grain weights. Shading cut down contemporaneously the provision of sucrose to the developing grain but, soon after return to full illumination, the supply of sucrose was restored to levels observed in ears that had not been shaded. Moreover, the estimated concentrations of sucrose in the endosperm of grains that accumulated less dry matter as a result of shading were higher than in endosperm filling on the unshaded plants. Although shading resulted in lighter grains, the grains contained just as much protein as the unshaded ones. Trimming the ears (by removing some spikelets) of shaded plants did not influence grain weight. These responses to shading are taken as evidence for the existence of a mechanism operating during the early stages of grain development, before grain-filling begins, which can influence the capacity of the endosperm to accumulate starch. Capacity to accumulate protein is evidently not subject to the same kind of control.