Sulphur nutrition affects delivery and metabolism of S in developing endosperms of wheat

Experiments were conducted to investigate the effect of S nutrition and ava ilability on the forms of S and N in the endosperm cavity and endosperm of wheat, and on the capacity of the endosperm to utilize those compounds for the synthesis of proteins. Plants were grown in solution culture with 2 mM N and either 200 muM S (high-S) or 50 muM S (low-S) and all nutrients were withdrawn at various times from booting until 8 d post-anthesis. Sulphate w as the major form of soluble S in the endosperm cavity and endosperm of hig h-S plants during the time of rapid grain development. By contrast, glutath ione (GSH) was the major form of soluble in the endosperm cavity and in the endosperm in low-S plants. Crude extracts of endosperm tissue from both hi gh-S and low-S plants supported (i) the hydrolysis of GSH to gamma -glutamy l cysteine and glycine, and of gamma -glutamyl cysteine to glutamate and cy steine, and (ii) sulphate-dependent PPi-ATP exchange and the sulphydration of O-acetylserine catalysed by ATP sulphurylase and cysteine synthase, resp ectively. High-S nutrition enhanced the in vitro rates of ATP sulphurylase and cysteine synthase.