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

Abstract

Summary 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 35 S fed to cotyledons by injection. After 35 S‐cysteine injection, c . 50% of the labelled S in the cotyledon was metabolized to 35 S‐sulphate. This reaction was partly inhibited by aminooxyacetic acid, an inhibitor of cysteine‐desulfhydrase. After 35 S‐sulphate application, c . 1% of the radiolabel was found in cysteine and glutathione in the cotyledon. After 2 h, c . 20% of the 35 S was transported into the root–shoot axis independently of whether 35 S‐sulphate or 35 S‐cysteine was injected into the cotyledon. After 4 h, 40% of 35 S 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.