Localisation of glutathione and homoglutathione in Medicago truncatula is correlated to a differential expression of genes involved in their synthesis

Glutathione (GSH) and homoglutathione (hGSH) were quantified in Medicago tr uncatula during plant development. hGSH was detectable only 48 h after seed germination whereas GSH was present in the dry seeds, indicating that only GSH is used for sulphur storage in seeds. The hGSH was detectable only in the underground part of mature plants whereas GSH was present in all the or gans. gamma-EC synthetase (gamma-ECS) and GSH synthetase (GSHS) activities were found in roots and leaves whereas hGSH synthetase (hGSHS) was found on ly in roots. Full-length cDNA encoding gamma-ECS and two partial cDNAs (gsh s1 and gshs2) showing high identity with GSHS were isolated in M. truncatul a. High gamma-ECS activity was detected in protein extracts of a gamma-ECS- deficient E. coli strain expressing the M. truncatula gamma-ECS. Northern b lot analysis showed that the gamma-ECS gene was similarly expressed in all the mature plant organs tested, whereas gshs1 had a higher expression in le aves and flowers and gshs2 was preferentially expressed in roots and nodule s. We hypothesise that gshs1 and gshs2 encode a GSHS and an hGSHS, respecti vely.