The biological functions of glutathione revisited in Arabidopsis transgenic plants with altered glutathione levels

A functional analysis of the role of glutathione in protecting plants from environmental stress was undertaken by studying Arabidopsis that had been g enetically modified to have altered glutathione levels. The steady-state gl utathione concentration in Arabidopsis plants was modified by expressing th e cDNA for gamma -glutamyl-cysteine synthetase (GSH1) in both the sense and antisense orientation. The resulting plants had glutathione levels that ra nged between 3% and 200% of the level in wild-type plants. Arabidopsis plan ts with low glutathione levels were hypersensitive to Cd due to the limited capacity of these plants to make phytochelatins. Plants with the lowest le vels of reduced glutathione (10% of wild type) were sensitive to as little as 5 muM Cd, whereas those with 50% wild-type levels required higher Cd con centrations to inhibit growth. Elevating glutathione levels did not increas e metal resistance. It is interesting that the plants with low glutathione levels were also less able to accumulate anthocyanins supporting a role for glutathione S-transferases for anthocyanin formation or for the vacuolar l ocalization and therefore accumulation of these compounds. Plants with less than 5% of wild-type glutathione levels were smaller and more sensitive to environmental stress but otherwise grew normally.