Drought stress affects photosynthesis, leading to significant decrease in crop productivity. In the current study, the importance of the cytochrome oxidase (COX) and alternative oxidase (AOX) pathways of the mitochondrial oxidative electron transport chain (mETC) for photosynthesis and reactive oxygen species (ROS) homeostasis was evaluated in the leaves of Pisum sativum plants exposed to drought stress for 3 days (D3), 6 days (D6), and 9 days (D9). While drought stress resulted in decreased CO₂ assimilation rates, leaf stomatal conductance, transpiration, and leaf intercellular CO₂ concentration in a stress-dependent manner, superimposition with mETC inhibitors, antimycin A (AA) and salicylhydroxamic acid (SHAM), aggravated the responses. Decreased chlorophyll content, photosynthesis, and RubisCO (RbcL) degradation during progressive drought and their aggravation upon AOX pathway restriction indicated the importance of the AOX pathway for photosynthetic activity. Compared with COX pathway inhibition, higher intracellular H₂O₂ and O ^⋅−₂ levels, and increased cell death upon restriction of the AOX pathway during D6 and D9 stress conditions correlating with the modulation in antioxidant enzyme activities, signify the essentiality of the AOX pathway for ROS maintenance at optimal levels. Further, increased AOX1a expression during D6 and D9 conditions along with increased AOX protein levels indicated the activation of the AOX pathway during drought stress. Decline in Fv/Fm, actual quantum yield of PSII (ФPSII), photochemical quenching (qP), non-photochemical quenching (NPQ), and electron transport rate (ETR) upon restriction of the COX and AOX pathways indicated the requirement of mETC activity for optimal photochemical activities not only under normal conditions but also under progressive drought conditions.

干旱胁迫影响光合作用，导致作物生产力显着下降。在当前的研究中，评估了线粒体氧化电子传递链（mETC）的细胞色素氧化酶（COX）和替代氧化酶（AOX）途径对光合作用和活性氧（ROS）稳态的重要性 表达增加以及 AOX 蛋白水平增加表明干旱胁迫期间 AOX 途径被激活。 COX 和 AOX 途径限制后 Fv/Fm、PSII 实际量子产率 (ФPSII)、光化学猝灭 (qP)、非光化学猝灭 (NPQ) 和电子传输速率 (ETR) 的下降表明需要 mETC 活性不仅在正常条件下而且在逐渐干旱的条件下也能实现最佳的光化学活性。AOX1a 水平，并且在 D6 和 D9 应激条件下限制 AOX 通路后细胞死亡增加抗氧化酶活性的调节表明 AOX 途径对于将 ROS 维持在最佳水平的重要性。此外，D6 和 D9 条件下 ₂^⋅− 和 O 更高₂O_{22<以应激依赖性方式浓度，与mETC抑制剂、抗霉素A（AA）和水杨异羟肟酸（SHAM）叠加，加剧了反应。持续干旱期间叶绿素含量、光合作用和 RubisCO (RbcL) 降解降低，并且 AOX 途径限制加剧，表明 AOX 途径对光合作用活动的重要性。与 COX 通路抑制相比，细胞内 H} 同化率、叶片气孔导度、蒸腾作用和叶片细胞间 CO₂ 植物暴露于干旱胁迫 3 天 (D3)、6 天 (D6) 和 9 天 (D9)。而干旱胁迫导致 CO豌豆