A role for homoglutathione in organic sulphur transport to the developing mung bean seed

The aim of this work was to identify the major forms of organic sulphur transported from the leaf of mung bean, Vigna radiata (L.) Wilczek, cv. Katjang Idjoe, to a developing fruit. After introduction of [³⁵S]sulphate into a leaf by flap-feeding, the labelled metabolites were extracted from the peduncle, seeds and pericarp of a fruit at the same node, as well as the leaf lamina and petiole. Thiol groups were blocked by reduction and carboxymethylation, and the amino compounds examined as dansyl derivatives by thin-layer chromatography and autoradiography. In all tissues except the leaf lamina, the major labelled compound was homoglutathione (HGSH) (γ-glutamylcysteinyl-β-alanine); in the lamina its precursor γ-glutamylcysteine predominated. Minor labelling was also found in cysteine, methionine and glutathione. These results suggest a major physiological role for HGSH in the transport of reduced sulphur to the developing mung bean seed.