Some biochemical properties of guaiacol peroxidases as modified by salt stress in leaves of salt-tolerant and salt-sensitive safflower (Carthamus tinctorius L.cv.) cultivars
The kinetics properties of guaiacol peroxidase (GP) and its isozymic pattern, and lipid peroxidation product were comparatively analyzed in two varieties of safflower (cv. M-CC-190 as salt-tolerant and cv. IL-111 as salt-sensitive cultivars) under normal and different concentrations of NaCl. The pH profile of GP activity in leaves extract of two cultivars in control and salt stressed plants showed different pattern of pH dependency with three maxima peaks at pH 4.5, 6.5 and 8 in salt-tolerant cultivar and two maxima peaks at pH 4.5 and 6.5 in salt-sensitive cultivar. Comparison of catalytic efficiency for GP between two cultivars at respective pH, showed that, salt-tolerant cultivar in both control and salt stressed condition
had higher catalytic efficiency than salt-susceptible cultivar. The GP activity on the gels revealed four and two isoforms of peroxidases in salt-tolerant and salt-sensitive cultivars, respectively. GPs increased their expression with higher levels of salinity. However, in salt-sensitive cultivar GPs expression exhibited threshold behavior, with increase expressions in isoenzymes up to a certain level of salinity (25 mM NaCl), followed by decrease to a level of expressions corresponding to the control groups. The levels of lipid peroxidation as indicated by thiobarbituric acid reactive substances (TBARS) were higher in the sensitive variety than the tolerant under control and NaCl salinity. The overall results obtained in this study suggest that, oxidative stress may play an important role in salt-stressed
safflower plants and that the greater protection of M-CC-190 leaves from salt-induced oxidative damage results, at least in part, through the increase of the GPs activity, catalytic efficiency and induction of specific isoenzymes (P1 and P4).
Key words: Safflower, guaiacol peroxidase, kinetics, isoenzymes, salt stress.