Analysis of adaptive mechanism in crops against desertification using NMR technique.

沙漠化问题导致生态系统失衡，导致可用于作物生产的水资源大量减少。豇豆是萨赫勒半干旱地区的主要作物。本文研究了干旱胁迫下豇豆核磁共振弛豫时间、光合参数与脱落酸相关基因表达的关系。豇豆和其他豌豆植物遭受水分胁迫后，豇豆叶片的蒸腾速率和水蒸气扩散导率在短时间内以极显著的速率降低。观察结果表明，豇豆对干旱胁迫反应迅速，通过蒸腾减少了水分损失。与光合作用参数相反，干旱胁迫下豇豆叶片中水分含量和表征水分子状态的^1H-NMR弛豫时间（T_1,T_2）保持不变或逐渐增加。接下来，我们重点研究了9-顺式环氧类胡萝卜素双加氧酶（NCED）和玉米黄质环氧化酶（ZEP）的基因表达谱，这两种酶都是ABA合成的关键酶。当豇豆和大豆遭受干旱胁迫时，豇豆根系中NCED mRNA的诱导时间比大豆根系早6 d，而ZEP仅在豇豆根系中被诱导。基于这些结果，我们认为干旱胁迫下豇豆根部会诱导ZEP和NCED，然后ABA水平的增加导致气孔快速关闭，从而有效保护其叶片免受水分流失（Iwaya-Inoue et al. 2006;Imamura et al. 2007,Proceedings）。也研究了蓝光依赖性气孔开启促进作物叶片萎蔫的机制（Takemiya et al. 2005,2006）。此外，还研究了种子作为最抗性器官的耐旱性（Funaba et al. 2006; Ishibashi and Iwaya-Inoue 2006）。

The problems of desertification cause imbalance in the ecosystem, resulting in a large decrease of water which could be used for crop production. Cowpea are major crops in the semi-arid zone of the Sahel. In this research the relationship between NMR relaxation times, photosynthetic parameters and expression of abscisic acid (ABA) related genes in cowpea plants induced by drought stress.When cowpea and other pea plant were subjected to water stress, transpiration rate and vapor diffusion conductance of cowpea leaves were reduced at significantly high rate in short time after the stress treatment. The observation indicates that cowpea lessened its water loss via transpiration by so quickly responsiveness to drought stress. In the contrast to the parameters of photosynthesis, water content and ^1H-NMR relaxation times (T_1,T_2) representing water molecule status in cowpea leaves were retained or gradually increased while cowpea was subjected to drought stress. In the next, we focused on gene expression profiles of 9-cis-epoxycarotenoid dioxygenase (NCED) and zeaxanthin epoxidase (ZEP) which are both key enzymes for synthesis of ABA. When cowpea and soybean were subjected to drought stress, induction of NCED mRNA was observed in cowpea roots 6 days earlier compared with that of soybean roots and ZEP is induced only in cowpea roots. Based on these results, it is suggested that ZEP and NCED are induced in cowpea roots under drought stress, and then increase of ABA levels leads to rapid stomatal closure, resulting in effective protection from water loss in its leaves (Iwaya-Inoue et al. 2006;Imamura et al. 2007,Proceedings). It was also studied that the mechanism of blue light-dependent stomatal opening which facilitates leaf wilting in crop plants (Takemiya et al. 2005,2006). Furthermore, drought tolerance in seeds as the most resistant organ was also investigated (Funaba et al. 2006,Ishibashi and Iwaya-Inoue 2006).