Physiological mechanisms controlling stress tolerance in maize

在过去的70年里，北美玉米的遗传产量每年提高约1%，这与抗逆性的提高直接相关。我们已经证明，在胁迫条件下，较新的玉米杂交种的抗逆性增强表现在包丝期间向穗和籽粒的干物质分配增强，以及叶片保持绿色和保持高叶片碳交换率的能力增强，这被称为功能性保持绿色。这两种性状对胁迫反应的生理机制可以通过检查除感兴趣的性状（即接近等基因系）以外在各方面都相等的玉米基因型来量化。本研究计划的目标是：(1)在大量基因型中评估胁迫对籽粒形成动力学和功能保持绿的影响的有效方法；(2)通过将有效程序应用于QTL定位群体来识别这些性状的QTL。(3)利用重组自交系（RILs）对胁迫的极端反应，量化核仁形成动力学和功能保绿的生理机制。目标#1下的研究结果很重要，因为目前评估任一性状的程序都非常复杂，无法实际应用于大量基因型（即，测量种群中单个植物的生长速度，以了解籽粒形成动态，并测量冠层内整个灌浆期的叶片碳交换率[CER]）。第二个目标下的研究结果将确定可用于第三个目标下的研究的风险评价指标。研究抗逆性反应的生理机制（即目标#3）将在我们的田间水培系统中进行，以便最大限度地控制环境变量，并深入研究整个生命周期的干物质积累和分配（包括根）以及叶片CER和荧光参数。测试的压力将包括水、氮和阴影压力。

Genetic yield improvement of maize in North America of about 1% per year during the past 70 years has been associated directly with increased stress tolerance. We have shown that increased stress tolerance in newer maize hybrids manifests itself under stressful conditions in enhanced dry matter partitioning to the ear and kernels during the period bracketing silking and in the enhanced ability of leaves to both stay green and to maintain high leaf carbon exchange rates, which is termed functional stay green. The physiological mechanisms that underlie the response of these two traits to stress can be quantified by examining maize genotypes that are equal in every respect other than the traits of interest (i.e., near isogenic lines). The objectives of the proposed research program are (1) to evaluate effective methodologies to assess effects of stress on both kernel-formation dynamics and functional stay green among large numbers of genotypes, (2) to identify QTLs for these traits by applying the effective procedures to QTL mapping populations, and (3) to quantify the physiological mechanisms underlying kernel-formation dynamics and functional stay green using recombinant inbred lines (RILs) at the extreme ends of the spectrum for their response to stress. Results of studies under Objective #1 are important because the current procedures to evaluate either trait are very complex and cannot be done practically for large number of genotypes (i.e., measuring growth rate of individual plants within a population for kernel-formation dynamics and measuring leaf carbon exchange rate [CER] throughout the grain-filling period within the canopy). Results of the studies under the second objective will identify RILs that can be used for the studies under the third objective. Studies on the physiological mechanisms underlying the stress tolerance response (i.e., Objective #3) will be carried out in our field hydroponic system in order to have maximum control over environmental variables and to enable in-depth investigations of dry matter accumulation and partitioning (including roots) and of leaf CER and fluorescence parameters throughout the life cycle. Stresses examined will include water, nitrogen and shade stress.