Aluminum (Al) toxicity is a major yield-limiting factor for crops in acidic soils. In this work, we have investigated the potential role of spermidine (Spd) on Al toxicity in rice chloroplasts. Exogenous Spd markedly reduced Al concentration and elevated other nutrient elements such as Mn, Mg, Fe, K, Ca, and Mo in chloroplasts of Al-treated plants. Meanwhile, Spd further activated arginine decarboxylase (ADC) activity of key enzyme in polyamine (PA) synthesis, and enhanced PA contents in chloroplasts. Spd application dramatically addressed Al-induced chlorophyll (Chl) losses, inhibited thylakoid membrane protein complexes degradation, especially photosystem II (PSII), and significantly depressed the accumulations of superoxide radical (O₂·^-), hydrogen peroxide (H₂O₂), and malondialdehyde (MDA) in chloroplasts. Spd addition activated antioxidant enzyme activities and decreased soluble sugar content in chloroplasts compared with Al treatment alone. Spd not only reversed the inhibition of photosynthesis-related gene transcript levels induced by Al toxicity, but diminished the increased expression of Chl catabolism-related genes. Furthermore, Chl fluorescence analysis showed that Spd protected PSII reaction centers and photosynthetic electron transport chain under Al stress, thus improving photosynthetic performance. These results suggest that PAs are involved in Al tolerance in rice chloroplasts and can effectively protect the integrity and function of photosynthetic apparatus, especially PSII, by mitigating oxidative damage induced by Al toxicity.

铝（Al）毒性是酸性土壤中农作物的主要产量限制因素。在这项工作中，我们调查了亚精胺（Spd）对水稻叶绿体中铝毒性的潜在作用。外源Spd显着降低了铝处理植物的叶绿体中的铝含量，并提高了其他营养元素，如锰，镁，铁，钾，钙和钼。同时，Spd进一步激活了多胺（PA）合成中关键酶的精氨酸脱羧酶（ADC）活性，并提高了叶绿体中PA含量。Spd的应用显着解决了铝诱导的叶绿素（Chl）损失，抑制类囊体膜蛋白复合物的降解，尤其是光系统II（PSII），并显着抑制了超氧自由基（O ₂ · ^-）和过氧化氢（H ₂O ₂）和叶绿体中的丙二醛（MDA）。与单独使用Al处理相比，添加Spd可以激活抗氧化酶活性并降低叶绿体中的可溶性糖含量。Spd不仅逆转了由铝毒性诱导的光合作用相关基因转录水平的抑制，而且减少了Chl分解代谢相关基因表达的增加。此外，Chl荧光分析表明，Spd在Al胁迫下保护PSII反应中心和光合电子传输链，从而提高了光合性能。这些结果表明，PA参与水稻叶绿体中的铝耐受性，并且可以通过减轻铝毒性引起的氧化损伤来有效保护光合装置，特别是PSII的完整性和功能。