PLANT-CELL RESPONSES TO HEAVY-METALS - MOLECULAR AND PHYSIOLOGICAL-ASPECTS

The effect of lead, cadmium and cooper on protein pattern, free radica ls and antioxidant enzymes in root of Lupinus luteus L. were investiga ted. Heavy metals inhibited growth of lupin roots, which was accompani ed by increased synthesis and accumulation of a 16 kDa polypeptide (Pr zymusinski et al. 1991 Biochem. Physiol. Pflanzen., 187:51-57). This c omponent has been earlier identified as immunologically related to Cu, Zn-superoxide dismutase (Przymusinski er al. 1995 Env.Exp.Bot., 35:485 -495). However, more detailed study revealed that this stress-stimulat ed protein is composed of four to six polypeptides of different electr ophoretic mobility. The most abundant polypeptides of the 16kDa region were found to be closely homologous to pathogen related proteins. The number and intensity of these polypeptides was highly variable in roo ts of individual seedlings, which suggests that they might represent s eparate allelic forms. Electron paramagnetic spectra revealed that at low lead concentrations the amplitude of the first derivative was simi lar to the control and distinctly increased at higher metal concentrat ions. On ther,ther hand, at the lower bad concentrations the activity of antioxidant enzymes increased, whereas at higher metal doses the en zyme activities did not raise further (SOD) or even dropped (CAT, APOX ). This implies that the responses of antioxidant system to lead is do se-dependent stimulated by low metal concentrations, whereas at the hi gher metal level the free radical emission is beyond the quenching cap acity of antioxidant enzymes, which in turn might contribute to the re duced root growth. The effect of various heavy metals: Pb2+, Cd2+ and Cu2+ on phytochelatins and antioxidant enzymes depends on the kind of metal ion. Pb2+ and Cd2+ stimulated the PCs formation whereas Cu2+ was not effective. On the other hand, in root exposed to Cu the activity of catalase (CAT) was the highest as was the production of H2O2. The s trong oxidative effect of Cu2+ ions which were not complexed by PCs su ggests that these peptides might by involved in the cellular defense s ystem by binding excessive heavy metal ions. On the basis of our resul ts it can be concluded that in lupin roots exposed to heavy metals the re is a complex defense system against metal phytotoxicity, which comp rises of specific proteins, antioxidant enzymes and phytochelatins.