Main Conclusion Plant growth-promoting bacteria association improved the enzymatic and non-enzymatic antioxidant pathways in Neotropical trees under drought, which led to lower oxidative damage and enhanced drought tolerance in these trees. Abstract Water deficit is associated with oxidative stress in plant cells and may, thus, negatively affect the establishment of tree seedlings in reforestation areas. The association with plant growth-promoting bacteria (PGPB) is known to enhance the antioxidant response of crops, but this strategy has not been tested in seedlings of Neotropical trees. We evaluated the effects of inoculation with two PGPB ( Azospirillum brasilense and Bacillus sp.) on the antioxidant metabolism of Cecropia pachystachya and Cariniana estrellensis seedlings submitted to drought. We measured the activity of antioxidant enzymes and the content of non-enzymatic antioxidants in leaves, and biometrical parameters of the seedlings. In both tree species, drought decreased the activity of antioxidant enzymes and the content of non-enzymatic antioxidant compounds. For C. pachystachya, the enzymatic and non-enzymatic pathways were mostly influenced by A. brasilense inoculation, which enhanced ascorbate peroxidase (APX) and superoxide dismutase activities and positively affected the level of non-enzymatic antioxidant compounds. In C. estrellensis , A. brasilense inoculation enhanced APX activity. However, A. brasilense and Bacillus sp. inoculation had more influence on the non-enzymatic pathway, as both bacteria induced a greater accumulation of secondary compounds (such as chlorogenic acid, gallic acid, rutin and synapic acid) compared to that in non-inoculated plants under drought. For both species, PGPB improved biometrical parameters related to drought tolerance, as specific leaf area and leaf-area ratio. Our results demonstrate that PGPB induced antioxidant mechanisms in drought-stressed Neotropical trees, increasing drought tolerance. Thus, PGPB inoculation provides a biotechnological alternative to improve the success of reforestation programmes.

中文翻译：

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植物促生菌改善干旱胁迫新热带树木叶片抗氧化代谢

主要结 摘要 缺水与植物细胞中的氧化应激有关，因此可能对造林区树苗的建立产生负面影响。已知与植物生长促进细菌 (PGPB) 的关联可增强作物的抗氧化反应，但该策略尚未在新热带树木的幼苗中进行测试。我们评估了接种两种 PGPB（Azospirillum brasilense 和 Bacillus sp.）对受旱天竺葵和 Cariniana estrellensis 幼苗抗氧化代谢的影响。我们测量了抗氧化酶的活性和叶片中非酶抗氧化剂的含量，以及幼苗的生物特征参数。在这两种树种中，干旱降低了抗氧化酶的活性和非酶抗氧化化合物的含量。对于 C. pachystachya，酶和非酶途径主要受 A. brasilense 接种的影响，这增强了抗坏血酸过氧化物酶 (APX) 和超氧化物歧化酶的活性，并对非酶抗氧化化合物的水平产生了积极影响。在 C. estrellensis 中，接种 A. brasilense 增强了 APX 活性。然而，A. brasilense 和 Bacillus sp。接种对非酶途径的影响更大，因为两种细菌都会诱导更多的次级化合物（如绿原酸、没食子酸、芦丁和突触酸）与干旱下未接种的植物相比。对于这两个物种，PGPB 改善了与耐旱性相关的生物特征参数，如比叶面积和叶面积比。我们的研究结果表明，PGPB 在干旱胁迫的新热带树木中诱导了抗氧化机制，从而提高了耐旱性。因此，PGPB 接种为提高重新造林计划的成功率提供了一种生物技术替代方案。