The Effect of Paraquat and Hypothermia on Norflurason-Resistant Mutants of Arabidopsis thaliana and Derived Cell Cultures

A tolerance to paraquat (PQ) of plants and cell cultures of Arabidopsis thaliana mutants, nfz18 and nfz24, obtained by chemical mutagenesis and selected by their tolerance to norflurason was demonstrated. This tolerance to PQ was manifested in less active peroxidation of lipids (POL), which was assessed by the content of thiobarbituric acid-reactive substances, and in a less degree of plant and callus damages, which was accompanied by a higher activity of superoxide dismutase and other antioxidant enzymes. A capability of norflurason-tolerant mutants to cross-adaptation toward PQ and activation of antioxidant enzymes indicate a genetically determined activation of the antioxidant systems, resulting in improved mutant tolerance to these inducers of oxidative stress. The nfz24 mutant was much more sensitive to hypothermia than wild-type plants and nfz18 mutants, which was expressed in a higher level of POL in plants and calluses and in a more rapid decrease in the suspension cell viability of this mutant. A similarity in the responses of plants and derived heterotrophic cultures to PQ and hypothermia indicates that, in these A. thaliana mutants, adaptation to these types of stresses occurs mainly at the cellular level. Possible reasons of increased sensitivity to hypothermia of the nfz24 mutant, which was more tolerant to the inducers of oxidative stress, PQ and norflurason, are discussed.