Effect of iron deficiency on S-adenosyl-methionine synthetase in barley roots

S-adenosyl-L-methionine (SAM) synthetase, which catalyzes methionine to SAM, is one of the enzymes involved in the biosynthesis of the mugineic acid-family phytosiderophores (MAs). The MAs are secreted from grass roots under iron (Fe)-deficient conditions. We compared the SAM synthetase activities between Fe-deficient and Fe-sufficient barley roots. However, no difference was observed. Then we performed Northern hybridization analysis between Fe-deficient and Fe-sufficient barley tissues by a cDNA fragment of SAM synthetase isolated from barley. No increase in the amount of mRNA was detected in the Fe-deficient barley roots as compared to the Fe-sufficient ones. It was suggested that the first step in the phytosiderophore biosynthesis induced under the Fe-deficiency is not SAM synthetase, but NA synthase and the second induced step is NA aminotransferase.