Liu Zhilei, Bi Shiting, Meng Jingrou, Liu Tingting, Li Pengfei, Yu Cailian, Peng Xianlong
College of Resources and Environment, Northeast Agricultural University, Harbin, China.
Key Laboratory of Germplasm Innovation, Physiology and Ecology of Grain Crop in Cold Region (Northeast Agricultural University), Ministry of Education, Harbin, China.
Front Plant Sci. 2022 Sep 28;13:962460. doi: 10.3389/fpls.2022.962460. eCollection 2022.
Arbuscular mycorrhizal fungi (AMF) are known to improve plant stress tolerance by regulating proline accumulation, and nitric oxide (NO) plays an important signaling role in proline metabolism. Environmental nitrogen (N) affects AMF colonization and its contribution to host plants resistance to stress conditions. However, the relationship between proline metabolism and NO in mycorrhizal rice and the effect of N application on symbiont proline metabolism under low temperature have not been established. Pot culture experiments with different temperature, N and exogenous NO donor treatments were conducted with non-mycorrhizal and mycorrhizal rice. The results showed that AMF enhanced rice proline accumulation under low-temperature stress and decreased glutamate (Glu) and ornithine (Orn) concentrations significantly. In comparison with non-mycorrhizal rice, AMF colonization significantly decreased the Glu concentration, but had little effect on the Orn concentration under low-temperature stress, accompanied by increasing expression of , and . Exogenous application of NO increased proline concentration both under normal and low temperature, which exhibited a higher increase in mycorrhizal rice. NO also triggered the expression of key genes in the Glu and Orn pathways of proline synthesis as well as proline degradation. Higher N application decreased the AMF colonization, and AMF showed greater promotion of proline metabolism at low N levels under low temperature stress by regulating the Glu synthetic pathway. Meanwhile, AMF increased rice nitrate reductase (NR) and nitric oxide synthase (NOS) activities and then enhanced NO accumulation under low N levels. Consequently, it could be hypothesized that one of the mechanisms by which AMF improves plant resistance to low-temperature stress is the accumulation of proline enhancement of the Glu and Orn synthetic pathways, with the involvement of the signaling molecule NO. However, the contribution of AMF to rice proline accumulation under low-temperature stress was attenuated by high N application.
丛枝菌根真菌（AMF）可通过调节脯氨酸积累来提高植物的胁迫耐受性，而一氧化氮（NO）在脯氨酸代谢中发挥着重要的信号传导作用。环境氮（N）会影响AMF的定殖及其对宿主植物抗逆性的贡献。然而，菌根水稻中脯氨酸代谢与NO之间的关系以及低温下施氮对共生体脯氨酸代谢的影响尚未明确。本研究对非菌根和菌根水稻进行了不同温度、氮素及外源NO供体处理的盆栽试验。结果表明，AMF在低温胁迫下增强了水稻脯氨酸的积累，并显著降低了谷氨酸（Glu）和鸟氨酸（Orn）的浓度。与非菌根水稻相比，AMF定殖显著降低了低温胁迫下的Glu浓度，但对Orn浓度影响较小，同时伴随着 、 和 的表达增加。外源施加NO在正常温度和低温条件下均提高了脯氨酸浓度，在菌根水稻中增幅更高。NO还触发了脯氨酸合成的Glu和Orn途径以及脯氨酸降解关键基因的表达。较高的施氮量降低了AMF的定殖，而AMF在低温胁迫下通过调节Glu合成途径在低氮水平时对脯氨酸代谢的促进作用更大。同时，AMF提高了水稻硝酸还原酶（NR）和一氧化氮合酶（NOS）的活性，进而在低氮水平下增强了NO的积累。因此，可以推测AMF提高植物抗低温胁迫能力的机制之一是脯氨酸的积累 增强Glu和Orn合成途径，并涉及信号分子NO。然而，高施氮量减弱了AMF在低温胁迫下对水稻脯氨酸积累的贡献。
