Heat stress is a common form of stress suffered by plants. Therefore, plants have evolved mechanisms to cope with the problems caused by high temperatures. In this study, the involvement of calcium ion and calmodulin (Ca²⁺-CaM) in the protection against heat stress-induced oxidative damage in tomato (Solanum lycopersicum L.) seedlings was investigated. Treatment of tomato leaves with short-term heat stress led to significant increase in the level of malondialdehyde (MDA) and protein oxidation (in terms of carbonyl groups), two important parameters of oxidative stress. However, such oxidative processes were mitigated by pretreatment with Ca²⁺ and aggravatedby pretreatment with the Ca²⁺ chelator ethylene glycol-bis(β-amino ethyl ether)-N,N,N’,N’-tetraacetid acid (EGTA), the Ca²⁺ channel blockers lanthanum chloride(LaCl₃), or the CaM antagonists chlorpromazine (CPZ), trifluoperazine (TFP) and N-(6-aminohexyl)-5-chloro-1-naphthalenesul-fonamide (W7). Besides, Ca²⁺pretreatment significantly reduced the accumulation of reactive oxygen species (ROS), O₂^.- and H₂O₂ and remarkably induced the total activities of the antioxidant enzymes superoxide dismutase (SOD) and ascorbate peroxidase (APX) under heat stress, while EGTA, LaCl₃, CPZ, TFP and W7 pretreatment reversed them. The results obtained here suggest that Ca²⁺-CaM signaling pathways are involved in resistance to heat stress-induced oxidative stress by regulation of antioxidant mechanisms in tomato leaves.

Key words: Calcium, calmodulin, heat stress, oxidative stress, Solanum lycopersicum L.