Reduced glutathione is a novel regulator of vernalization-induced bolting in the rosette plant Eustoma grandiflorum

The transition from the vegetative rosette stage to the reproductive growth stage (bolting) in the rosette plant Eustoma grandiflorum has a strict requirement for vernalization, a treatment that causes oxidative stress. Since we have shown that reduced glutathione (GSH) and its biosynthesis are associated with bolting in another rosette plant Arabidopsis thaliana, we here investigated whether a similar mechanism governs the vernalization-induced bolting of E. grandiflorum. Addition of GSH or its precursor cysteine, instead of vernalization, induced bolting but other thiols, dithiothreitol and 2-mercaptoethanol, did not. The inductive effect of vernalization on bolting was nullified by addition of buthionine sulfoximine (BSO), an inhibitor of GSH synthesis, without decreasing the plant growth rate. BSO-mediated inhibition of bolting was reversed by addition of GSH but not by cysteine. These indicate that vernalization-induced bolting involves GSH biosynthesis and is specifically regulated by GSH. Plant GSH increased during the early vernalization period along with the activity of gamma-glutamylcysteine synthetase that catalyzes the first step of GSH biosynthesis, although there was little change in amounts of GSH precursor thiols, cysteine and gamma-glutamylcysteine. These findings strongly suggest that vernalization stimulates GSH synthesis and synthesized GSH specifically determines the bolting time of E. grandiflorum.