稻米品质形成对高CO2浓度和高温的应答及其生理机制

The increases in atmospheric carbon dioxide (CO2) concentrations and air temperature are the two most important attributes of global climate change. Previous chamber studies indicated an overall deterioration in grain quality by elevated CO2 concentration, but its physiological mechanism as well as whether such changes in grain quality would be altered by growth temperature were unclear. The recently developed T-FACE (Temperature-Free Air CO2 Enrichment) system provides us an opportunity to study the effects of atmospheric environment changes on rice quality and its mechanism under the completely open field condition. We will use T-FACE technology to increase the CO2 concentration and temperature of rice canopy simultaneously. Different cultivars will be used to study CO2 concentration, temperature and their interaction on grain quality formation of rice. In addition, the temporal variation in fine structures of rice starch (including starch grain morphology, structure and starch chain length distribution) and protein (protein components and amino acids) will be examined. In particular, the physiological mechanism responsible for rice quality changes under elevated CO2 concentration and temperature will be studied through investigating the key enzyme activity and main hormone concentration during grain filling stage. The relationship between these responses of starch and protein, enzyme activity, hormone concentration and grain quality will be analyzed to reveal the mechanism of rice quality formation in response to the elevated atmospheric CO2 concentration, temperature and the both. This prospective study will enhance our ability to predict the response of rice to atmospheric changes, and to develop a more effective adaptation strategy to cope with climate change.

持续升高的大气CO2浓度和温度是全球气候变化的两个重要特征。气室研究表明，CO2浓度升高使稻米品质总体变劣，但这种趋势是否因生长温度而异？内在机理如何？目前尚不明确。最新出现的大型T-FACE系统在完全开放的大田条件下运行，为探明大气环境变化对稻米品质的实际影响及其机制提供了契机。本项目采用T-FACE技术同时增高水稻冠层CO2浓度和温度，研究高CO2浓度、温度及二者互作对不同水稻品种稻米品质的影响；同时以灌浆过程为主线，动态监测稻米淀粉（包括淀粉粒形态、结构及淀粉链长分布等）及蛋白含量（蛋白组分及氨基酸）的变化；解析这些响应与籽粒碳代谢关键限速酶活性及主要激素浓度变化的关系；并综合灌浆期淀粉和蛋白性状、酶活性及主要激素浓度的响应等方面揭示稻米品质形成过程对大气CO2浓度或/和温度升高的应答机制。本研究将利于增强对未来大气变化情景下水稻响应的预测能力，进而更有效制订应对气候变化的适应策略。

全球大气CO2浓度和温度持续升高。但高CO2浓度及高温对稻米品质影响的普遍性和机制尚不清楚？本研究基于完全开放的大田T-FACE平台，系统研究了不同水稻品种稻米品质对高CO2浓度及高温的响应规律，并重点从淀粉分子结构及灌浆生理方面深入研究了其影响机制。结果表明，高CO2浓度显著改善了稻米蒸煮食味品质，降低了矿质元素生物有效性，而对杂交稻的影响远大于常规稻。大气CO2浓度平均使不同类型水稻品种稻米垩白度及蛋白质含量极显著降低44.7%、10.4%，其中粳稻响应最大。高CO2浓度对稻米品质的影响并不能通过蛋白质和直链淀粉含量的变化解释。在粳稻上的深入研究发现：高CO2浓度及高温显著增大了粳稻稻米淀粉颗粒，二因子同时处理时增幅更大。尽管二因子没改变淀粉晶体类型，但改变了淀粉分子有序度：高CO2浓度使淀粉1045/1022 cm-1及1022/995 cm-1平均分别显著降低2.6%和3.3%，而显著增大结晶度4%。高CO2浓度使SSS及GBSS酶活性分别显著增加28.0%和27.9%，导致淀粉长链结构及淀粉粒体积增大；高CO2浓度亦使乙烯释放速率显著降低28.5%，进而使SBE酶活性降低7.5%，结果导致淀粉分子中的α-1’6 糖苷键减少，淀粉蓝值和淀粉双链结构增加。相关分析结果表明，淀粉粒形态及分子结构的改变或是稻米淀粉热力学指标及米饭口感改变的一个重要原因：高CO2浓度多显著增加了淀粉糊化时的转变温度及崩解值，显著降低热焓值和消减值，最终使米饭口感改善8.2%。高温及高温与高CO2浓度互作效应对这些指标的影响小且多不显著，预示着人们或高估了未来环境下高温对稻米品质（至少对食味品质）的负面效应。本研究结果对未来气候条件下稻米食味品质的适应策略具有重要意义。