Sulfur Metabolism in Plants

This chapter describes the major metabolic pathways of sulfur (S) compounds in plants, and their relations to each other and to other processes. It emphasizes the flow of S from into S compounds. Transport of SO4 2- and organic S compounds is included because it is closely associated with S metabolism. The activation of SO4 2- by ATP sulfurylase, as the first reaction in SO4 2- metabolism is a logical point for the regulation of its metabolism. The major products of SO4 2- reduction in the leaves are cysteine, methionine, and glutathione. In plants, reduction is of major importance, whereas the formation of sulfate esters is less important. The metabolites of sulfur dioxide in the leaf were translocated to the roots in the phloem. A major portion of cysteine S is transferred to methionine, and the bulk of both cysteine and methionine is incorporated into proteins, where cysteine plays a vital role in the secondary structure.