%0 Journal Article
%T Common Bean (Phaseolus vulgaris L.) Accumulates Most S-Methylcysteine as Its ¦Ã-Glutamyl Dipeptide
%J Plants | An Open Access Journal from MDPI
%D 2019
%R https://doi.org/10.3390/plants8050126
%X The common bean ( Phaseolus vulgaris) constitutes an excellent source of vegetable dietary protein. However, there are sub-optimal levels of the essential amino acids, methionine and cysteine. On the other hand, P. vulgaris accumulates large amounts of the ¦Ã-glutamyl dipeptide of S-methylcysteine, and lower levels of free S-methylcysteine and S-methylhomoglutathione. Past results suggest two distinct metabolite pools. Free S-methylcysteine levels are high at the beginning of seed development and decline at mid-maturation, while there is a biphasic accumulation of ¦Ã-glutamyl- S-methylcysteine, at early cotyledon and maturation stages. A possible model involves the formation of S-methylcysteine by cysteine synthase from O-acetylserine and methanethiol, whereas the majority of ¦Ã-glutamyl- S-methylcysteine may arise from S-methylhomoglutathione. Metabolite profiling during development and in genotypes differing in total S-methylcysteine accumulation showed that ¦Ã-glutamyl- S-methylcysteine accounts for most of the total S-methylcysteine in mature seed. Profiling of transcripts for candidate biosynthetic genes indicated that BSAS4;1 expression is correlated with both the developmental timing and levels of free S-methylcysteine accumulated, while homoglutathione synthetase ( hGS) expression was correlated with the levels of ¦Ã-glutamyl- S-methylcysteine. Analysis of S-methylated phytochelatins by liquid chromatography and high resolution tandem mass spectrometry revealed only small amounts of homophytochelatin-2 with a single S-methylcysteine. The mitochondrial localization of phytochelatin synthase 2¡ªpredominant in seed, determined by confocal microscopy of a fusion with the yellow fluorescent protein¡ªand its spatial separation from S-methylhomoglutathione may explain the lack of significant accumulation of S-methylated phytochelatins. View Full-Tex
%U https://www.mdpi.com/2223-7747/8/5/126