College of Life Science, Shenyang Normal University, Shenyang, 110034, China.
College of Chemistry and Chemical Engineering, Shenyang Normal University, Shenyang, 110034, China.
Ecotoxicol Environ Saf. 2020 Dec 1;205:111350. doi: 10.1016/j.ecoenv.2020.111350. Epub 2020 Sep 19.
Atmospheric nitrogen dioxide (NO) negatively affects plant (crop) growth and development, as well the yield and quality in some regions or environments. Arbuscular mycorrhizal fungus (AMF)-mediated amelioration of NO-induced plant damage has been reported, but the underlying mechanisms remained unclear. This study explored the beneficial effect of AMF symbiosis on tomato plant responses to NO at physiology, biochemistry, and gene expression, with an emphasis on nitrate metabolism, antioxidative defense, and photosynthetic performance. Pot-grown plants were used in the experiments, which were performed in laboratory from February to November 2019. NO fumigation with a dose of 10 ± 1 ppm was carried out after 50 d of plant growth, and data were collected following 8 h of fumigation. NO fumigation (+NO) and AMF inoculation (+AMF), alone and especially in combination (NO + AMF), increased the gene expression of nitrate- and nitrite reductase, and their enzymatic activity in leaves, such as by 61%, 27%, and 126% for the activity of nitrate reductase, and by 95%, 37%, and 188% for nitrite reductase, respectively, in +NO, +AMF, and AMF + NO plants relative the control (-NO, -AMF) levels. Following NO exposure, +AMF leaves displayed stronger activities of superoxide dismutase, peroxidase and catalase, and higher content of glutathione and ratio of its reduced form to oxidized form, as compared with -AMF ones. Correspondingly, lesser oxidative damage was detected in +AMF than in -AMF plants, as indicated by the contents of HO and malondialdehyde, electrolyte leakage, also by in situ visualization for the formation of HO, superoxide anion, and dead cells. The increased antioxidative capacity in +AMF plants was correlated with enhanced expression of antioxidation-related genes. Exposure to NO substantially impaired photosynthetic processes in both + AMF and -AMF plants, but an obvious mitigation was observed in the former than in the latter. For example, the total chlorophyll, net photosynthetic rate, stomatal conductance, and ribulose-1,5-bisphosphate carboxylase activity were 18%, 27%, 26%, and 40% higher, respectively, in +AMF than in -AMF plants under NO stress. The differential photosynthetic performance was also revealed by chlorophyll fluorescence imaging. We analyzed the expression patterns of some genes related to photosynthesis and carbon metabolisms, and found that all of them exclusively presented a higher expression level in +AMF plants relative to -AMF ones under NO stress. Taken together, this study provided evidence that AMF symbiosis played a positively regulatory role in host plant responses to NO, probably by increasing leaf nitrate metabolism and antioxidative defense, and maintaining the photosynthetic efficiency to some extent, wherein the transcription regulation might be a main target.
大气中的二氧化氮（NO）会对植物（作物）的生长和发育以及一些地区或环境中的产量和质量产生负面影响。已报道丛枝菌根真菌（AMF）介导的对 NO 诱导的植物损伤的改善作用，但潜在机制仍不清楚。本研究从生理学、生物化学和基因表达方面探讨了 AMF 共生对番茄植物对 NO 响应的有益影响，重点研究了硝酸盐代谢、抗氧化防御和光合作用。实验采用盆栽植物，于 2019 年 2 月至 11 月在实验室进行。在植物生长 50 天后，用 10 ± 1 ppm 的剂量进行 NO 熏气，并在熏气 8 小时后收集数据。NO 熏气（+NO）和 AMF 接种（+AMF）单独以及特别是组合（NO + AMF）增加了叶片中硝酸盐和亚硝酸盐还原酶的基因表达及其酶活性，例如，与对照（-NO，-AMF）水平相比，硝酸盐还原酶的活性增加了 61%、27%和 126%，亚硝酸盐还原酶的活性增加了 95%、37%和 188%。在暴露于 NO 后，与 -AMF 叶片相比，+AMF 叶片的超氧化物歧化酶、过氧化物酶和过氧化氢酶活性更高，谷胱甘肽含量更高，其还原形式与氧化形式的比例更高。因此，与 -AMF 植物相比，+AMF 植物中的氧化损伤较小，这表现为 HO 和丙二醛、电解质泄漏的含量，以及 HO、超氧阴离子和死细胞形成的原位可视化。+AMF 植物中增强的抗氧化能力与抗氧化相关基因的表达增强有关。NO 的暴露严重损害了+AMF 和 -AMF 植物的光合作用过程，但前者的损害明显小于后者。例如，在 NO 胁迫下，+AMF 植物的总叶绿素、净光合速率、气孔导度和核酮糖-1,5-二磷酸羧化酶活性分别提高了 18%、27%、26%和 40%。在叶绿素荧光成像中也揭示了不同的光合作用性能。我们分析了一些与光合作用和碳代谢相关的基因的表达模式，发现与 -AMF 植物相比，在 NO 胁迫下，所有这些基因在+AMF 植物中的表达水平都更高。总的来说，这项研究提供了证据表明，AMF 共生在宿主植物对 NO 的响应中发挥了积极的调节作用，可能是通过增加叶片硝酸盐代谢和抗氧化防御，并在一定程度上维持光合作用，其中转录调控可能是主要目标。
