The involvement of polyphenols and peroxidase activities in heavy-metal accumulation by epidermal glands of the waterlily (Nymphaeaceae)

Co-localization of polyphenols and peroxidase activity was demonstrated in epidermal glands of the waterlily (Nymphaea) by histochemistry. Total pheno ls, tannins and peroxidase activity were determined quantitatively in plant extracts. Polyphenols were partially identified and were found to consist mainly of hydrolyzable tannins, gallic and tannic acid derivatives. Nymphae a polyphenols were shown to chelate Cr, Hg, and Pb in vitro, and Cd-binding by polymerized polyphenols was demonstrated in leaves exposed to Cd in viv o. Both polyphenols and peroxidases were found at very high constitutive le vels, which were not induced or altered by external conditions, such as lig ht and heavy-metal stress. It is suggested that the polymerization of polyp henols by peroxidases, enhanced after heavy-metal uptake and detoxification , is responsible for the binding of heavy metals in Nymphaea epidermal glan ds.