Incorporation of C-14 into methionine as an intermediate for phytosiderophore biosynthesis in barley

In order to verify the precursory role of methionine (Met) in the biosynthe sis of the mugineic acid family of phytosiderophores (MAs), feeding experim ents of C-14-labeled compounds to barley (Hordeum vulgare L. cv. Minorimugi ) roots grown hydroponically were conducted. When both C-14-Glucose (Glc) a nd unlabeled Met were fed to segmented roots, C-14 was incorporated into Me t and MAs in the roots. Molar-radioactivity of Met was higher than that of the amino-butanoic-acid unit in MAs in the roots. When C-14-Glc and unlabel ed homoserine (Hse) were fed to decapitated roots,C-14 was incorporated int o Met but not into Hse. Therefore, it was considered that Hse might not be a major precursor of MAs. In addition,C-14 was incorporated into Met and MA s in the roots when both C-14-glycerol (Gol) and unlabeled Met were fed to segmented roots. It is suggested that MAs may be synthesized from Glc via M et, bypassing Hse, and that the MAs biosynthesis may involve an unknown pat hway associated with Gol and leading to Met.