The effect of Absizik acid on the induced thermotolerance in the maize seedlings and its relationship with calcium ion and antioxidant systems

In this experiment, the effect of ABA and Calcium ion on thermotolerance of corn seedlings and its relationship with antioxidant enzyms was investigated. ABA treatment significantly increased thermotolerance in maize seedlings. Pretreatment of maize seeds with CaCl[2] solution, which raises calcium content of maize seedlings, further enhanced the ABA-induced thermotolerance. In contrast, pretreatment with the Ca[2+]chelator EGTA, which lowers calcium content of maize seedlings, decreased the ABA-induced thermotolerance. In addition, pretreatment with the plasma membrane Ca[2+] channel blockers La[3+] and verapamil, which are expected to inhibit the influx of extracellular Ca[2+] into cells, also weakened the ABA-induced thermotolerance in maize seedlings. However, the calmodulin antagonists W7 and CPZ had little effect on the ABA-induced thermotolerance Measurement of activities of the antioxidant enzymes SOD, CAT, APX and GPX and the level of lipid peroxidation (in terms of MDA) indicated that heat stressinduced an oxidative stress in maize seedlings. ABA treatment enabled maize seedlings to maintain higher activities of these antioxidant enzymes and a lower level of lipid peroxidation at normal culture temperature and under heat stress. Ca[2+] pretreatment further enhanced the ABA-induced increase in SOD and APX activities and lowered the heat stress-induced lipid peroxidation in the ABA-treated seedlings, but EGTA pretreatment had an inverse effect. These results suggested that the ABA-induced thermotolerance is mediated by Ca[2+] and requires the entry of extracellular Ca[2+] into cells across the plasma membrane.An antioxidant enzyme systems cause the increase in the ABA and decrease of the induced thermotolerance.