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

In order to verify the precursory role of methionine (Met) in the biosynthesis of the mugineic acid family of phytosiderophores (MAs), feeding experiments of ¹⁴C-Iabeled compounds to barley (Hordeum vulgare L. cv. Minorimugi) roots grown hydroponically were conducted. When both ^l4C-Glucose (Glc) and unlabeled Met were fed to segmented roots, ¹⁴C was incorporated into Met 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 ^l4C-Glc and unlabeled homoserine (Hse) were fed to decapitated roots, l4C was incorporated into Met but not into Hse. Therefore, it was considered that Hse might not be a major precursor of MAs. In addition, ¹⁴C was incorporated into Met and MAs in the roots when both ¹⁴C-glycerol (Gol) and unlabeled Met were fed to segmented roots. It is suggested that MAs may be synthesized from Glc via Met, bypassing Hse, and that the MAs biosynthesis may involve an unknown pathway associated with Gol and leading to Met.