S nutrition affects the pools of S available to developing grains of wheat

Developing grains of rain-fed wheat must obtain S from reserves that the pl ant accumulated during vegetative growth. The effect of S nutrition on the sources of S that were transported from vegetative tissues during grain dev elopment was examined. Wheat was grown in solution culture with 2 mM N and either 200 mu M S (high-S) or 50 mu M S (low-S). All nutrients were withdra wn either at booting, ear emergence, anthesis, or 8 d post anthesis. Plants were harvested at 13 or 25 d post anthesis. At 13 d post anthesis, high-S plants contained sulphate in roots and leaves, GSH (glutathione) in leaves, and S in leaf proteins. Between harvests, sulphate was lost from roots and GSH was lost from leaves. Sulphate and GSH were not detected in roots or l eaves of low-S plants at 13 d post anthesis, and between harvests, S in lea f-proteins decreased, During reproductive growth, redistribution of sulphat e from roots was likely to be in response to S demand, redistribution of GS H was likely to result from the breakdown of chloroplasts, and in low-S pla nts, hydrolysis of leaf proteins in response to N demand was the most impor tant source of S for grain development.