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%，这与耐胁迫性的提高直接相关。我们已经表明，在新的玉米杂交种增加的胁迫耐受性表现在胁迫条件下，在穗和籽粒的干物质分配在此期间包围吐丝和在增强的能力，既保持绿色和保持高的叶片碳交换率，这被称为功能性保持绿色。作为这两个性状对胁迫的响应的基础的生理机制可以通过检查除了感兴趣的性状之外在各个方面都相等的玉米基因型（即，近等基因系）。本研究的主要目的是：（1）在大量的基因型中，评价胁迫对籽粒形成动态和功能性持绿绿色的影响的有效方法;（2）通过对QTL定位群体的有效分析，确定这些性状的QTL，（3）利用重组自交系（RILs）对籽粒形成动态和功能性持绿色的生理机制进行定量分析处于压力反应的极端。目标#1下的研究结果是重要的，因为目前评估任一性状的程序非常复杂，并且实际上不能对大量基因型（即，测量群体内单个植物的生长速率以获得籽粒形成动力学，以及测量冠层内整个灌浆期的叶碳交换速率（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区域一体化土地。 对胁迫耐受反应的生理机制的研究（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，并能够深入研究整个生命周期中的干物质积累和分配（包括根）以及叶CER和荧光参数。研究的压力包括水、氮和遮荫压力。

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.