Plant Physiol, July 2001, Vol. 126, pp. 1275-1280

Homo-Phytochelatins Are Synthesized in Response to Cadmium in Azuki Beans¹

Matja Oven, Klaus Raith, Reinhard H.H. Neubert, Toni M. Kutchan, and Meinhart H. Zenk^*

Institut für Pflanzenbiochemie, Weinberg 3, D-06120 Halle, Germany (M.O., T.M.K.); Institut für Pharmazeutische Technologie und Biopharmazie, Universität Halle, Wolfgang-Langenbeck-Strasse 4, D-06120 Halle, Germany (K.R., R.H.H.N.); and Biozentrum-Pharmazie, Universität Halle, Weinbergweg 22, D-06120 Halle, Germany (M.H.Z.)

In a recent report, it was claimed that azuki beans (Vigna angularis) do not synthesize phytochelatins (PCs) upon exposure to cadmium, although glutathione (GSH), the substrate for PC synthesis, is present in this plant. This legume species thus would be the first exception in the plant kingdom that would fail to complex heavy metals by PCs. Here, we report that not GSH, but only homoglutathione can be detected in this plant and that homo-phytochelatins are formed when azuki beans are challenged with heavy metals such as cadmium. We also show that the 5,5'-dithiobis(2-nitrobenzoic acid)-oxidized GSH reductase recycling assay, used for GSH quantification in the recent study of heavy metal tolerance in azuki beans, reacts both with GSH and homoglutathione and therefore cannot be used when biological samples should be analyzed exclusively for GSH.