ROLE OF ANTIOXIDANT SYSTEMS AND JUVENILITY IN TOLERANCE OF PLANTS TO DISEASES AND ABIOTIC STRESSES

Juvenility of plant tissues enhances resistance to toxins, cell wall-d egrading enzymes, autolysis of membrane lipids and thereby to necrotro phic pathogens. Moreover, inhibition of senescence by high doses of NO 3-nitrogen or decapitation increased superoxide dismutase (SOD) enzyme activity and decreased the rate of lipid peroxidation in tobacco plan ts. The oxidative stress caused by the herbicide acifluorfen treatment induced a higher increase in level of non-protein thiols and in activ ity of the antioxidant enzymes glutathione-reductase, GSH S-transferas e and ascorbate-peroxidase in leaves of superoxide (paraquat) tolerant (PT) than of sensitive (PS) tobaccos. PT plants showed not only enhan ced juvenility, but also increased tolerance to many biotic and abioti c stresses. On the other hand, decapitation, or treatment of tobacco p lants: by kinetin or benzyladenine increased the tolerance to the oxid ative stress caused by paraquat. The importance of juvenility of plant tissues in resistance to biotic and abiotic stresses was emphasized b y the elevated tolerance to paraquat, fusaric acid and to B. cinerea o f transformed tomato plants with enhanced cytokinin and auxin producti on.