Sulfate assimilation and glutathione synthesis in C4 plants

Sulfate assimilation and glutathione synthesis were traditionally believed to be differentially compartmentalised in C-4 plants with the synthesis of cysteine and glutathione restricted to bundle sheath and mesophyll cells, respectively. Recent studies, however, showed that although ATP sulfurylase and adenosine 5' phosphosulfate reductase, the key enzymes of sulfate assimilation, are localised exclusively in bundle sheath in maize and other C-4 monocot species, this is not true for the dicot C-4 species of Flaveria. On the other hand, enzymes of glutathione biosynthesis were demonstrated to be active in both types of maize cells. Therefore, in this review the recent findings on compartmentation of sulfate assimilation and glutathione metabolism in C-4 plants will be summarised and the consequences for our understanding of sulfate metabolism and C-4 photosynthesis will be discussed.