Homo-phytochelatins are synthesized in response to cadmium in Azuki beans

In a recent report, it was claimed that azuki beans (Vigna angularis) do no t synthesize phytochelatins (PCs) upon exposure to cadmium, although glutat hione (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, b ut only homoglutathione can be detected in this plant and that homo-phytoch elatins are formed when azuki beans are challenged with heavy metals such a s cadmium. We also show that the 5,5 ' -dithiobis (2-nitrobenzoic acid)-oxi dized GSH reductase recycling assay, used for GSH quantification in the rec ent study of heavy metal tolerance in azuki beans, reacts both with GSH and homoglutathione and therefore cannot be used when biological samples shoul d be analyzed exclusively for GSH.