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%，这与提高抗逆性直接相关。结果表明，在胁迫条件下，新玉米杂交种的抗逆性增强，表现为在围栏吐丝期干物质分配到穗和籽粒中的增加，以及叶片保持绿色和维持较高的叶碳交换速率的能力增强，这被称为功能性保绿。这两个性状对逆境反应的生理机制可以通过检查除感兴趣的性状(即近等基因系)外在所有方面都相同的玉米基因型来量化。该研究计划的目标是(1)评估有效的方法来评估胁迫对大量基因型的籽粒形成动态和功能保持绿色的影响，(2)通过将有效的程序应用于QTL定位群体来确定这些性状的QTL，以及(3)利用光谱极端端的重组自交系(RIL)来量化影响籽粒形成动态和功能保持绿色的生理机制。目标1下的研究结果很重要，因为目前评估这两个性状的程序都非常复杂，而且不能对大量的基因类型进行实际操作(即测量群体内单个植株的生长速度以进行籽粒形成动态，并测量冠层内整个灌浆期的叶碳交换率[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铁路系统。为了最大限度地控制环境变量，并能够在整个生命周期中深入研究干物质积累和分配(包括根)以及叶片CER和荧光参数，将在我们的田间水培系统中开展对胁迫耐性反应的生理机制的研究(即目标#3)。研究的胁迫包括水分、氮素和遮荫胁迫。

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.