施钾增强水稻抵抗叶鞘腐败病的碳代谢机制

Increasing the application of potassium (K) fertilizer could improve crop disease resistance as a result of improving the degree of cell lignification and promoting the synthesis of macromolecular compound. Leaf sheath rot disease is a fungal disease which occurs particularly serious in the nitrogen excessive or K deficient soils. K fertilization decreased significantly the incidence of leaf sheath rot which was related to not only the previous confirmation, but also the tissue organ of the disease (sword leaf sheath, storage of the nutrients). K probably played a specific role in regulating the transport of metabolites to resist pathogen hijacking nutrients. This project will study the effects of K application on the species of carbon (sugar) metabolites before the pathogen infection using metabolomics method with field trials and pot experiments inoculated with pathogen. The 14C isotopic tracer technique was used to study the influences of K application on the translocation rate and distribution of flag leaf carbon assimilate (sucrose) in the flag leaf sheath at the initial stage of infection. The non-invasive micro-measurement technique was used to study the K+ flux inside and outside the sheath cells of pathogen and its relationship with the loading of carbon assimilates in the phloem. Quantitative study will be conducted to explore the competition for carbon assimilates of pathogen growth and grain-filling at different K levels in the late stage of infection. Finally, the K concentration threshold for increasing the resistance of rice to leaf sheath rot disease will be established. This will provide the theoretical basis for scientific K fertilization of rice.

施用钾肥可提高作物的抗病性，通常认为钾能改善细胞木质化程度和促进高分子化合物合成。叶鞘腐败病是一种真菌性病害，在氮肥过量或缺钾的土壤上尤为严重，增施钾肥显著降低其发病率。除前人已确认的原因外，还与发病部位（旗叶鞘、养分储存库）有关，钾在调节碳代谢产物转运以抵抗病原菌对养分劫持的过程中可能发挥了特异性作用。本项目通过田间试验和室内接种帚枝霉菌培养试验，采用代谢组学方法研究病原菌侵染前施钾对碳（糖）代谢产物种类的影响；利用14C同位素示踪重点研究侵染初期施钾对旗叶碳同化物（蔗糖）在旗叶鞘中的转运速率及分布的影响；应用非损伤微测技术研究病原菌入侵时叶鞘组织细胞内外K+流向及其与碳同化物在韧皮部装载的关系；定量研究侵染后期不同钾水平下病原菌生长与籽粒灌浆对碳同化物的竞争，阐明施钾调节碳（糖）代谢抵抗帚枝霉菌侵染叶鞘的机制。建立以提高水稻抗叶鞘腐败病为导向的钾素浓度阈值，为科学施用钾肥提供理论依据。

叶鞘腐败病是一种真菌性病害，在氮肥过量或缺钾的土壤上尤为严重，增施钾肥显著降低其发病率。除前人已确认的原因外，还与发病部位（旗叶鞘、养分储存库）有关，钾在调节碳代谢产物转运以抵抗病原菌对养分劫持的过程中可能发挥了特异性作用。本项目通过田间试验和室内接种帚枝霉菌培养试验，研究了病原菌侵染前施钾对碳（糖）代谢的影响；帚枝霉菌侵染初期钾素营养对碳代谢产物韧皮部转运的影响；帚枝霉菌侵染后期不同施钾处理对碳（糖）代谢物再分配的影响；基于提高水稻对叶鞘腐败病自身抗性的钾素营养浓度阈值。主要研究结果如下：1）施钾促进了染病水稻茎秆非结构性碳水化合物向籽粒运输，降低了染病叶鞘的碳氮比，增强了寄主的碳代谢。与不施钾处理（-K）相比，施钾增加了染病水稻茎秆非结构性碳水化合物的表观转运量（ATMNSC），增幅为53.3%-57.0%。茎秆钾浓度维持在1.53%-1.74%，可显著增加ATMNSC以缓解染病造成的结实率损失。2）施钾通过减弱侵染对细胞膜的损伤而保障蔗糖在染病叶鞘的运输。未侵染时，与-K处理相比，施钾处理叶鞘丙二醛含量和相对电导率分别降低了28.2%和20.8%；而侵染后，降幅为39.5%和33.7%。施钾缓解了侵染对细胞膜完整性和通透性的破坏，促进了蔗糖的运输。3）施钾通过维持侵染点脂质稳态而缓解染病叶鞘的腐烂。与供钾充足的叶鞘相比，侵染后，缺钾叶鞘腐烂速率增加了50.2%；1-烷基-2-酰基甘油磷酸乙醇胺和亚油酸的含量提高了约18倍。充足的钾素供应增加了抗氧化剂谷胱甘肽合成相关基因的表达，维持了侵染点的脂质稳态且缓解了叶鞘的腐烂。综上，充足的钾素营养供应通过增强寄主的碳代谢、促进茎秆非结构性碳水化合物往籽粒的运输、促进谷胱甘肽等抗氧化剂的合成和提高叶片糖脂含量提升了寄主对叶鞘腐败病的抗性。项目阐明了施钾调节碳代谢抵抗帚枝霉菌侵染叶鞘的机制，建立了以提高水稻抗叶鞘腐败病为导向的钾素浓度阈值，对水稻科学施用钾肥具有重要理论和实践意义。