Abstract: Effect of Ca²⁺-CaM on the thermotolerance induced by SA in young grape seedling swas studied. The levels of antioxidant enzymes, MDA, CaM, proline were measured after the treatments. The results showed that SA could induce the thermotolerance of grape seedlings and Ca²⁺ enhanced the SA-induced thermotolerance. In contrast, pretreatment with the Ca²⁺ chelator EGTA, the plasmalemma Ca²⁺ channel blocker La³⁺ , which was expected to inhibit the influx of extracellular Ca²⁺ into cells, and the CaM antagonist W7 weakened the SA-induced thermotolerance. Under heat shock, pretreatment with SA or Ca²⁺ ( SA + Ca²⁺ ) increased the level of CaM in leaves, but EGTA ( SA + EGTA) , La³⁺ ( SA + La³⁺ ) or W7 ( SA +W7) decreased the levels of CaM. SA pretreatment enabled seedlings to maintain higher activities of SOD and CAT,
and a lower level of MDA to weaken oxidative stress induced by heat shock. Ca²⁺ pretreatment further enhanced the SA-induced increase of SOD or CAT activity, but EGTA, La³⁺ and W7 had a contrary effect. POD or APX activity of each treatment had little change before and after heat shock. In addition, pretreatment with SA or Ca²⁺ ( SA +Ca²⁺ ) enhanced the content of proline and kept higher level under heat shock, the level of proline in each seedling pretreated with antagonists had no obvious difference to the control. These results showed that SA-induced thermotolerance was medicated by Ca²⁺ and required the entry of extracellular Ca²⁺ into cells through plasmalemma, and was related with antioxidant enzymes and proline.

Key words: Grape, Seedling, Calcium, Calmodulin, Salicylic acid, Thermotolerance, Antioxidant