Sulphur assimilation and effects on yield and quality of wheat

Deficiency of sulphur (S) has been recognised as a limiting factor for crop production in many regions in the world. In particular, incidence of S deficiency has increasingly been reported in Brassica and cereal crops in Western Europe over the last decade, mainly as a consequence of a massive decrease of atmospheric S inputs. The S requirement of wheat is about 15-20 kg/ha for optimum growth. Reproductive growth of wheat appears to be more sensitive to S deficiency than vegetative growth, with decreased grain size under S-limiting conditions. In addition to the effects on yields, the S status of wheat grain is an important parameter for the quality of wheat products. Limiting S availability has been shown to favour the synthesis and accumulation of Spoor or low-S storage proteins such as omega-gliadin and high molecular weight (HMW) subunits of glutenin at the expense of S-rich proteins. Sulphur deficiency also decreases the proportion of polymeric proteins in total proteins, but shifts the distribution of polymeric proteins toward lower molecular weight. These changes in protein composition are associated with alterations of dough rheology. Significant responses of breadmaking quality to the addition of S fertilisers have been established under field conditions. Recent studies have also shown that breadmaking quality correlated more closely with grain S concentration than with N concentration. Recent progress in cloning genes encoding components involved in sulphate uptake and assimilation has substantially increased our understanding of plant S nutrition and its regulation, and opened up opportunities for manipulation of S uptake and metabolism in plants. (C) 1999 Academic Press.