Hydroponic treatment with salicylic acid decreases the effects of chillinginjury in maize (Zea mays L.) plants

The addition of 0.5 mM salicylic acid (SA) to the hydroponic growth solutio n of young maize (Zea mag's L.) plants under normal growth conditions provi ded protection against subsequent low-temperature stress. This observation was confirmed by chlorophyll fluorescence parameters and electrolyte leakag e measurements. In addition, 1 d of 0.5 mM SA pre-treatment decreased net p hotosynthesis, stomatal conductivity and transpiration at the growth temper ature (22/20 degrees C). Since there was only a slight decrease in the rati o of variable to maximal fluorescence (F-v/F-m) the decrease in photosynthe tic activity is not due to a depression in photosystem II. The analysis of antioxidant enzymes showed that whereas SA treatment did not cause any chan ge in ascorbate peroxidase (EC 1.11.1.11) and superoxide dismutase (EC 1.15 .1.1) activities, there was a decrease in catalase (EC 1.11.1.6) activity, and an increase in guaiacol peroxidase (EC 1.11.1.7) and glutathione reduct ase (EC 1.6.4.2) activities after the 1-d SA treatment at 22/20 degrees C. In native polyacrylamide gels there was, among the peroxidase isoenzymes, a band which could be seen only in SA-treated plants. It is suggested that t he pre-treatment of maize plants with SA at normal growth temperature may i nduce antioxidant enzymes which lead to increased chilling tolerance.