Metabolism of reduced and inorganic sulphur in pea cotyledons and distribution into developing seedlings

Abstract

Sulphur export and redistribution from the cotyledons of pea (Pisum sativum) seedlings was investigated to determine the role of cotyledons as a sulphur source during root-shoot axis development. Thiols and sulphate were analysed using standard biochemical techniques, and 35S fed to cotyledons by injection. After 35S-cysteine injection, c. 50% of the labelled S in the cotyledon was metabolized to 35S-sulphate. This reaction was partly inhibited by aminooxyacetic acid, an inhibitor of cysteine-desulfhydrase. After 35S-sulphate application, c. 1% of the radiolabel was found in cysteine and glutathione in the cotyledon. After 2 h, c. 20% of the 35S was transported into the root-shoot axis independently of whether 35S-sulphate or 35S-cysteine was injected into the cotyledon. After 4 h, 40% of 35S was found outside the cotyledon. Cotyledons of pea seedlings are capable of sulphate assimilation and cysteine degradation. Both sulphate and reduced sulphur were allocated from the cotyledons to the developing tissues of the pea seedlings. © New Phytologist (2000).