Root uptake, transport, and metabolism of externally applied glutathione in Phaseolus vulgaris seedlings.

The most abundant thiol in beans (Phaseolus vulgaris L. cv. Saxa) is the tripeptide homoglutathione (hGSH) rather than glutathione (GSH). At the whole-plant level the GSH content is less than 0.5% of the hGSH content. In the present study GSH was supplied to the roots of bean seedlings to test whether GSH can be taken up by roots and transported to the shoot. Therefore, 12-day-old plants were exposed to 1 mmol/L GSH for 4, 8 and 24 h prior to harvest. In response to this GSH exposure, elevated GSH contents were found in all tissues. After 4 h the GSH content increased in the roots from 1 +/- 1 to 22 +/- 2 nmol GSH g(-1) fresh weight (FW), in the leaves from 2 +/- 1 to 9 +/- 4 nmol GSH g(-1) FW, and in the apex from 30 +/- 5 to 75 +/- 4 nmol GSH g(-1) FW. These data indicate that GSH is taken up by bean roots and is transported to above above-ground parts of the plants. Roots exposed to GSH for 24 h contained 2-fold higher cysteine (Cys) and hGSH contents than the controls. Apparently, GSH taken up by the roots is not only loaded into the xylem but also partially degraded and used for hGSH synthesis.