Wu Chao, Cui Kehui, Wang Wencheng, Li Qian, Fahad Shah, Hu Qiuqian, Huang Jianliang, Nie Lixiao, Mohapatra Pravat K, Peng Shaobing
National Key Laboratory of Crop Genetic Improvement, MOA Key Laboratory of Crop Ecophysiology and Farming System in the Middle Reaches of the Yangtze River, Huazhong Agricultural University Wuhan, China.
National Key Laboratory of Crop Genetic Improvement, MOA Key Laboratory of Crop Ecophysiology and Farming System in the Middle Reaches of the Yangtze River, Huazhong Agricultural UniversityWuhan, China; Hubei Collaborative Innovation for Grain Industry, JingzhouChina.
Front Plant Sci. 2017 Mar 17;8:371. doi: 10.3389/fpls.2017.00371. eCollection 2017.
Cytokinins (CTKs) regulate panicle size and mediate heat tolerance in crops. To investigate the effect of high temperature on panicle CTK expression and the role of such expression in panicle differentiation in rice, four rice varieties (Nagina22, N22; Huanghuazhan, HHZ; Liangyoupeijiu, LYPJ; and Shanyou63, SY63) were grown under normal conditions and subjected to three high temperature treatments and one control treatment in temperature-controlled greenhouses for 15 days during the early reproductive stage. The high temperature treatments significantly reduced panicle CTK abundance in heat-susceptible LYPJ, HHZ, and N22 varieties, which showed fewer spikelets per panicle in comparison with control plants. Exogenous 6-benzylaminopurine application mitigated the effect of heat injury on the number of spikelets per panicle. The high temperature treatments significantly decreased the xylem sap flow rate and CTK transportation rate, but enhanced cytokinin oxidase/dehydrogenase (CKX) activity in heat-susceptible varieties. In comparison with the heat-susceptible varieties, heat-tolerant variety SY63 showed less reduction in panicle CTK abundance, an enhanced xylem sap flow rate, an improved CTK transport rate, and stable CKX activity under the high temperature treatments. Enzymes involved in CTK synthesis (isopentenyltransferase, LONELY GUY, and cytochrome P450 monooxygenase) were inhibited by the high temperature treatments. Heat-induced changes in CTK transportation from root to shoot through xylem sap flow and panicle CTK degradation via CKX were closely associated with the effects of heat on panicle CTK abundance and panicle size. Heat-tolerant variety SY63 showed stable panicle size under the high temperature treatments because of enhanced transport of root-derived CTKs and stable panicle CKX activity. Our results provide insight into rice heat tolerance that will facilitate the development of rice varieties with tolerance to high temperature.
细胞分裂素（CTKs）调控作物的穗大小并介导耐热性。为了研究高温对穗部CTK表达的影响以及这种表达在水稻穗分化中的作用，在温度可控的温室中，于生殖早期对四个水稻品种（Nagina22，N22；黄花占，HHZ；两优培九，LYPJ；汕优63，SY63）进行正常条件下的种植，并设置三种高温处理和一种对照处理，持续15天。高温处理显著降低了热敏感品种LYPJ、HHZ和N22中的穗部CTK丰度，与对照植株相比，这些品种的每穗小穗数较少。外源施用6-苄基腺嘌呤减轻了热害对每穗小穗数的影响。高温处理显著降低了木质部汁液流速和CTK运输速率，但提高了热敏感品种中的细胞分裂素氧化酶/脱氢酶（CKX）活性。与热敏感品种相比，耐热品种SY63在高温处理下穗部CTK丰度降低较少，木质部汁液流速增强，CTK运输速率提高，且CKX活性稳定。参与CTK合成的酶（异戊烯基转移酶、孤独蛋白和细胞色素P450单加氧酶）受到高温处理的抑制。高温诱导的通过木质部汁液流动从根到地上部的CTK运输变化以及通过CKX介导的穗部CTK降解与高温对穗部CTK丰度和穗大小的影响密切相关。耐热品种SY63在高温处理下穗大小稳定，这是因为根源CTK的运输增强以及穗部CKX活性稳定。我们的结果为水稻耐热性提供了见解，这将有助于培育耐高温水稻品种。
