灌浆期增温下后期施氮对粳米垩白的调控效应及其机制研究

Japonica rice has high chalky rate and chalkiness in the south of China, which is the key factor that restricts rice excellent quality formation, and this problem will become severer with climate warming. Our previous study found that the application of nitrogen fertilizer at heading stage significantly reduced rice chalky rate and chalkiness without affecting yield. Based on the discovery above, this study compares chalk characteristics and physicochemical properties of rice grains between the treatments of normal temperature, elevated temperature and elevated temperature + different nitrogen levels using representative japonica varieties cultivated in the south of China, with the aim to clarify the physicochemical basics of inhibiting effects of late nitrogen application on rice chalk under high temperature. From the aspects of carbon metabolism and nitrogen metabolism, the development dynamics of starch granule and protein body were investigated, and the dynamics of key enzyme activity and gene expression involved in the two metabolisms during grain-filling period were analyzed, the protein expression differences during the critical period of chalk formation between treatments were also detected. The results should elucidate the regulation mechanism of late nitrogen application on japonica rice chalk under elevated temperature. Additionally, this research will enhance the mechanisms of rice quality formation and regulation, and provide reference for rice cultivation under abiotic stress.

南方粳稻垩白率、垩白度较高，已成为制约稻米优质生产的关键限制因子，且这一问题在气候变暖的趋势下愈发严峻。申请者前期研究发现，灌浆期温度升高下，抽穗期施氮可在不影响产量的条件下显著降低稻米垩白。本项目拟在此基础上，以南方粳稻的代表性品种为材料，比较常温、增温、增温+抽穗期不同用量氮素等处理下籽粒垩白性状和理化特性的差异，探究灌浆期高温下后期施氮调控籽粒垩白的理化基础。进而从碳代谢和氮代谢两方面切入，追踪籽粒淀粉粒和蛋白体发育过程，分析碳氮代谢关键酶活性、基因表达的动态特征，探查垩白形成关键时期籽粒蛋白质表达的差异，深入解析温度升高下后期施氮调控粳米垩白的生理机制。研究结果可拓展稻米品质的形成与调控机制，为水稻抗逆栽培提供参考。

我国南方粳稻常遇较高的灌浆温度，导致品质恶化、尤其是垩白率和垩白度偏高，且可能造成产量下降，如何通过简单有效的栽培措施应对这一问题已成为南方粳稻稳定优质生产的当务之急。本研究以武运粳31号为材料，分析了灌浆期温度升高4℃对水稻产量和品质的影响。结果表明灌浆期温度升高显著降低了水稻产量，千粒重和结实率下降是产量损失的主要原因，同时引起垩白率、垩白度、球蛋白和谷蛋白含量升高，整精米率和直链淀粉含量下降，导致稻米品质变差。灌浆期高温下通过抽穗期施氮降低了植株体温、增加了灌浆中期的Fv/Fm、提高了耗散过剩光能为热的能力，使水稻叶绿素含量和净光合速率维持相对较高的水平、并抑制了叶片光合能力的下降速度，促进同化物向籽粒转运，从而增加了千粒重，这有助于减少高温下产量损失。同时，灌浆期温度升高下通过抽穗期施氮显著提高了整精米率、必需氨基酸含量、粗脂肪含量，降低垩白率、垩白度和直链淀粉含量，改善了稻米加工品质、外观品质和营养品质，且提高施氮量对于缓解高温的负面影响具有更好的效果。2021年水稻灌浆期主要阶段自然温度近十年平均水平高近3℃，为本研究提供了理想的自然高温条件，我们在此条件下验证了抽穗期撒施氮肥和喷施叶面氮肥对于降低高温对米质的负面影响也具有积极作用，主要体现在对垩白性状的改善，但对产量无显著影响。研究还发现，灌浆期高温下于抽穗期补充氮肥可使功能叶光合能力较高且衰老慢、灌浆持续时间更长、籽粒发育更完善，同时籽粒直链淀粉含量和结晶度下降、大粒径淀粉粒比例上升、蛋白发育更充分填充淀粉体之间的空隙，这些与施氮降低垩白发生具有重要关系。研究结果可为南方粳稻优质栽培提供参考依据。