Azospirillum brasilense affects the antioxidant activity and leaf pigment content of Urochloa ruziziensis under water stress

ABSTRACT Water stress leads to the formation of reactive oxygen species, resulting in degradation of leaf pigments and cell death. This study aimed at assessing the oxidative enzyme activity and photosynthetic pigment content in seeds and/or leaves of Urochloa ruziziensis (syn. Brachiaria) inoculated with Azospirillum brasilense under water stress. Assessments of soluble proteins, chlorophylls a and b and carotenoid contents, as well as the activity of superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) enzymes, were conducted at the beginning of the water stress process and also under severe water stress and during plant rehydration. Seed inoculation showed a reduction in the action of SOD, under water stress, with an increase after rehydration. POD exhibited an activity greater than CAT in all the assessments, but it did not differ statistically under severe water stress. CAT activity increased under severe stress in all treatments, particularly for leaf inoculation. Chlorophyll a was slightly degraded, maintaining the levels of the irrigated control, while the chlorophyll b and carotenoid contents, in plants subjected to leaf inoculation with A. brasilense, were higher under water stress. It was concluded that the leaf inoculation of U. ruziziensis with A. brasilense makes the plant more efficient at removing reactive oxygen species and protecting chlorophyll a.

摘要 水分胁迫可诱导活性氧（reactive oxygen species, ROS）的生成，进而引发叶片色素降解与细胞死亡。本研究旨在评估水分胁迫条件下，接种巴西固氮螺菌（Azospirillum brasilense）的鲁齐臂形草（Urochloa ruziziensis，异名Brachiaria）的种子及/或叶片中的氧化酶活性与光合色素含量。研究分别在水分胁迫起始阶段、严重水分胁迫阶段以及植株复水期间，对可溶性蛋白、叶绿素a、叶绿素b与类胡萝卜素含量，以及超氧化物歧化酶（superoxide dismutase, SOD）、过氧化物酶（peroxidase, POD）和过氧化氢酶（catalase, CAT）的酶活性进行了测定。种子接种处理在水分胁迫下可降低SOD活性，而复水后该酶活性有所上升。在所有评估节点中，POD活性均高于CAT，但在严重水分胁迫条件下二者活性无统计学差异。所有处理组的CAT活性在严重胁迫下均有所升高，尤以叶片接种处理组的升高最为显著。叶绿素a仅发生轻微降解，仍维持与灌溉对照组相当的水平；而经叶片接种A. brasilense的植株，其叶绿素b与类胡萝卜素含量在水分胁迫条件下更高。本研究结论表明，利用A. brasilense对U. ruziziensis进行叶片接种，可提升植株清除活性氧的效率，并对叶绿素a起到保护作用。