Salicylic acid-induced heat or cold tolerance in relation to Ca2+ homeostasis and antioxidant systems in young grape plants

Exogenous salicylic acid (SA) pretreatment decreased thiobarbituric acid-reactive substances (TBARS) and relative electrolyte leakage (REL) in grape leaves under heat or cold stress, indicating that SA can induce intrinsic heat or cold tolerance in grape. Exogenous SA pretreatment enabled the grape leaves to maintain relatively higher activities of ascorbate peroxidase (APX), glutathione reductase (GR), monodehydroascorbate (MDHA), and redox ratio in the ascorbate–glutathione pool under normal temperature and under heat or cold stress. The ultrastructural localization of Ca2+ in mesophyll cells of grape plants was examined with the improved Ca2+ antimonite precipitate method. The results showed cytosolic Ca2+ in SA-treated mesophyll cells was greater than that in controls at the normal temperature. After cold or heat stress, increased cytosolic Ca2+ in SA-treated mesophyll cells was pumped back to vacuoles or intercellular spaces, and chloroplast structure was not destroyed. When increased cytosolic Ca2+ in the control cells was not pumped back to vacuoles or intercellular spaces, chloroplast structure was destroyed. SA-treated cells can maintain Ca2+ homeostasis under cold or heat stress and increased tolerance. It is suggested that Ca2+ homeostasis and antioxidant systems are involved in salicylic acid-induced heat or cold tolerance in grape plants.