Rapid incorporation of ¹⁴C of glucose into phytosiderophores in iron-deficient barley roots

Abstract

Feeding experiments with ¹⁴C-labeled compounds were conducted to clarify the biosynthetic pathway of methionine for the production of the mugineic acid family of phytosiderophores (MAs) assuming that glucose may be converted to MAs through the glycolytic pathway, TCA cycle, and homoserine. Carbon-14 labeled glucose or homoserine was fed to intact roots of iron-deficient barley (Hordeum vulgare L. cv. Minorimugi) plants, and ¹⁴C-labeled glucose, malate, succinate, pyruvate, or glycerol was fed to excised roots of iron-deficient barley. In the feeding experiment with ¹⁴C-glucose using intact roots, ¹⁴C of glucose was incorporated into MAs rapidly and the molar radioactivity of the amino butanoic acid unit (C-4 unit) of the MAs was higher than that of citrate and malate. Carbon-14 of homoserine was incorporated into threonine rather than into MAs. Carbon-14 of malate, succinate, or pyruvate fed to the excised roots was not incorporated into MAs, while ¹⁴C of glycerol was incorporated into MAs. It was suggested that MAs may be synthesized from glucose through an unknown pathway that bypasses the organic acids of the TCA cycle, aspartate and homoserine; and that glycerol may be involved in the unknown pathway.

Key Words:

• biosynthesis
• glucose
• glycerol
• iron deficiency
• phytosidero-phore