Calcium (Ca²⁺) is involved in mediating anti-stress responses in plants through one or combination of biochemical processes. Thus, the major objective of present study was to assess the protective effect of exogenous Ca²⁺ (0, 2.5, 5.0, and 7.5 mM) on photosynthetic machinery of cv. Jaguar and SER-16 under heat stress (HS 25–45 °C for 48 h). The applied HS (45 °C) caused substantial reduction in net photosynthetic rate (Pn 73%), photosystem II quantum yield (ΦII 24%), linear electron flow (LEF 13%), and SPAD values (27%) with imbalancing of sugars metabolism and redox potential. At heat stress (40 °C), plants of both cultivars tried to acclimate by regulating leaf temperature through increased stomatal conductance (g_s 36%), transpiration rate (E 60%) and by increase in non-photochemical quenching (NPQ 19%). In addition, Ca²⁺ pre-treatment protected the membrane from oxidative damage by up-regulating the enzymatic activities and down-regulation of malondialdehyde (MDA) accumulation and electrolyte leakage in plant leaf tissues. Pre-treatment with Ca²⁺ enhanced the accumulation of sugars (glucose, fructose, inositol, and raffinose) in both heat stressed bean plants (45 °C). In conclusion, cv. Jaguar had greater tolerance to HS than SER-16, which is associated with Ca²⁺-induced photo-protective effect on PSII, the balance between LEF and reactive oxygen species (ROS) generation with concomitant up-regulation of antioxidant enzymes, and increase in compatible solutes. Based on changes in physiological attributes, it is speculated that Ca²⁺ application might have mediated thermo-tolerance in plants via Ca²⁺-sensing and signaling pathway, which needs to be verified through molecular studies.

钙（Ca ²⁺）通过一种或多种生物化学过程参与介导植物的抗应激反应。因此，本研究的主要目的是评估外源Ca ²⁺（0、2.5、5.0和7.5 mM）对cv光合作用机制的保护作用。Jaguar和SER-16在热应力下（HS 25–45°C持续48 h）。施加的HS（45°C）导致净光合速率（P n 73％），光系统II量子产率（ΦII 24％），线性电子流（LEF 13％）和SPAD值（27％）大大降低。糖代谢失衡和氧化还原潜力。在热胁迫（40°C）下，两个品种的植物都试图通过增加气孔导度（g_s 36％），蒸腾速率（E 60％）和非光化学猝灭（NPQ 19％）的增加。此外，Ca ²⁺预处理可通过上调酶活性，下调植物叶片组织中丙二醛（MDA）的积累和电解质的泄漏来保护膜免受氧化损伤。Ca ²⁺预处理可提高两种高温胁迫的豆类植物（45°C）中糖（葡萄糖，果糖，肌醇和棉子糖）的积累。总之，简历。捷豹对HS的耐受性高于SER-16，这与Ca ^2+有关诱导的对PSII的光保护作用，LEF和活性氧（ROS）生成之间的平衡以及抗氧化酶的上调，以及相容性溶质的增加。基于生理特性的变化，推测Ca ^2+的应用可能通过Ca ^2+的传感和信号传导途径介导了植物的耐热性，这需要通过分子研究加以验证。