DataSheet_1_CO2 Elevation Accelerates Phenology and Alters Carbon/Nitrogen Metabolism vis-à-vis ROS Abundance in Bread Wheat.docx

Wheat is an important staple food crop of the world and it accounts for 18–20% of human dietary protein. Recent reports suggest that CO2 elevation (CE) reduces grain protein and micronutrient content. In our earlier study, it was found that the enhanced production of nitric oxide (NO) and the concomitant decrease in transcript abundance as well as activity of nitrate reductase (NR) and high affinity nitrate transporters (HATS) resulted in CE-mediated decrease in N metabolites in wheat seedlings. In the current study, two bread wheat genotypes Gluyas Early and B.T. Schomburgk differing in nitrate uptake and assimilation properties were evaluated for their response to CE. To understand the impact of low (LN), optimal (ON) and high (HN) nitrogen supply on plant growth, phenology, N and C metabolism, ROS and RNS signaling and yield, plants were evaluated under short term (hydroponics experiment) and long term (pot experiment) CE. CE improved growth, altered N assimilation, C/N ratio, N use efficiency (NUE) in B.T. Schomburgk. In general, CE decreased shoot N concentration and grain protein concentration in wheat irrespective of N supply. CE accelerated phenology and resulted in early flowering of both the wheat genotypes. Plants grown under CE showed higher levels of nitrosothiol and ROS, mainly under optimal and high nitrogen supply. Photorespiratory ammonia assimilating genes were down regulated by CE, whereas, expression of nitrate transporter/NPF genes were differentially regulated between genotypes by CE under different N availability. The response to CE was dependent on N supply as well as genotype. Hence, N fertilizer recommendation needs to be revised based on these variables for improving plant responses to N fertilization under a future CE scenario.

小麦是全球重要的主食粮食作物，其所贡献的蛋白质占人类膳食总蛋白质的18%~20%。已有研究报道显示，CO₂浓度升高（CO₂ elevation, CE）会降低小麦籽粒的蛋白质及微量营养元素含量。本课题组前期研究发现，一氧化氮（nitric oxide, NO）生成量增加，同时硝酸还原酶（nitrate reductase, NR）与高亲和性硝酸盐转运蛋白（high affinity nitrate transporters, HATS）的转录本丰度及酶活性均出现伴随性下降，这一现象介导了CO₂浓度升高诱导的小麦幼苗氮代谢物含量降低。在本研究中，我们选取了两个硝酸盐吸收与同化特性存在显著差异的面包小麦基因型：Gluyas Early与B.T. Schomburgk，评估其对CO₂浓度升高环境的响应。为明确低氮（low nitrogen, LN）、适氮（optimal nitrogen, ON）与高氮（high nitrogen, HN）供应水平对植株生长、物候期、碳氮代谢、活性氧（Reactive Oxygen Species, ROS）与活性氮物种（Reactive Nitrogen Species, RNS）信号通路及产量的影响，我们分别通过短期（水培试验）与长期（盆栽试验）条件下的CO₂浓度升高处理，对不同供氮条件下的小麦植株表现进行了测评。试验结果显示，CO₂浓度升高可改善B.T. Schomburgk的植株生长状态，调控其氮同化过程、碳氮比与氮利用效率（nitrogen use efficiency, NUE）。整体而言，无论供氮水平如何，CO₂浓度升高均会降低小麦地上部氮浓度与籽粒蛋白质含量。CO₂浓度升高会加快两个供试小麦基因型的物候进程，使其提早开花。在CO₂浓度升高环境下生长的植株，其亚硝基硫醇与活性氧（ROS）水平显著升高，这一效应在适氮与高氮供应条件下尤为突出。CO₂浓度升高会下调光呼吸氨同化相关基因的表达；而在不同氮素有效性条件下，CO₂浓度升高对硝酸盐转运蛋白/NPF家族基因表达的调控模式在两个基因型间存在显著差异。综上，小麦对CO₂浓度升高的响应同时依赖于供氮水平与基因型背景。因此，在未来CO₂浓度升高的全球变化情景下，需结合上述两类变量优化氮肥施用方案，以提升植株对氮肥的利用响应效果。