Impact of soil nitrate and chloride content on transpiration of crop plants (Acronym: “An-Trans”)

在欧洲许多地区，农业面临着两大挑战：农作物可能会遭遇土壤水资源的逐渐匮乏，同时，一些地区的作物必须获得较少的氮素供应，以防止地下水和地表水受到硝酸盐的污染。这两个挑战是相互关联的，因为低土壤水分可利用性将减少蒸腾作用和质量流驱动的养分吸收，如硝酸盐(NO3−)和氯(Cl−)。反过来，叶片中NO3-−和Cl-−的吸收已被证明影响气孔运动，从而对作物的水分利用产生重要影响。在设想的项目中，将在双子叶植物豆科蚕豆和谷类大麦两种作物上研究土壤N3−-to-Cl−比率与气孔运动的关系。由于大麦气孔关闭依赖于质外体中的NO_3−，而双子叶植物则未发现这一要求，因此这两种作物对NO_3-−和Cl-−调节气孔导度的依赖性可能不同。此外，目前还不清楚大麦还是蚕豆保卫细胞更喜欢吸收NO_3−而不是氯−来驱动气孔开放。该项目将通过离子、代谢产物和激素分析(WP_2)、单细胞实验(WP_3)和单一运输蛋白(WP_4)分析四个工作包(WP)来研究土壤中NO_3−与Cl_−比率对气孔的影响。在WP1中，土壤中不同的NO3−-to-Cl−比率之间的关系将与我们的模式植物调节气孔运动和叶片水分的能力有关。在WP2中，我们将研究不同的NO3−与ClABA的比例对叶质外体和保卫细胞共质体的离子、代谢产物和激素浓度的影响，而WP3将研究阴离子组成(NO3−，ClABA)在何种程度上影响气孔运动。我们将测试蚕豆和大麦的保卫细胞是否更喜欢N3−或Cl−，以伴随驱动气孔运动的渗透过程。最后，WP4将侧重于NPF转运体在保卫细胞摄取NO3−和ClCl2以及释放这些阴离子的类SlaC1型阴离子通道中的作用。虽然SlaC1样通道在气孔运动的调节中发挥了重要作用，但NPF-蛋白吸收保卫细胞中的NO3−和Cl−的信息很少。我们的项目结果将有助于预测土壤逐渐干旱和土壤中NO3-−-N输入的减少对双子叶植物和粮食作物蒸腾作用的影响。通过这种方式，可以提供机械信息，这些信息可以集成到对气孔导度和水分消耗具有极好调节能力的作物的育种计划中。

In many parts of Europe, agriculture is facing two major challenges: crop plants are likely to encounter progressive soil water scarcity and, at the same time, crops in some areas must be supplied with less nitrogen to prevent groundwater and surface water pollution by nitrates. Both challenges are interrelated, since low soil water availability will reduce transpiration and the mass-flow driven uptake of nutrients such as nitrate (NO3−) and chloride (Cl−). In return, the uptake, i.e. the presence of NO3− and Cl− in the leaf, has been shown to affect stomatal movements and thus will have an important impact on water usage by crops. In the envisaged project, the relationship between the soil NO3−-to-Cl− ratio and stomatal movements will be studied on two crop plants; the dicotyledonous legume broad bean and the cereal barley. Both crops are likely to differ in their dependence on NO3− and Cl− for regulation of the stomatal conductance, since stomatal closure in barley depends on NO3− in the apoplast, while this requirement has not been found for dicotyledonous plants. Moreover, it is not known if barley or broad bean guard cells prefer the uptake of NO3− over Cl−, to drive stomatal opening.The project will study the impact of the NO3−-to-Cl− ratio in the soil on stomata in four work packages (WPs), which span the range of experiment with whole plants (WP1) via ion, metabolite and hormone analysis (WP2), single cell experiments (WP3) to the analysis of single transport proteins (WP4). In WP1, the relation between different NO3−-to-Cl− ratios in the soil will be linked to the ability of our model plants to regulate both stomatal movements and leaf hydration. In WP2, we will study to which extend different NO3−-to-Cl− ratios affect the ion, metabolite and hormone (ABA) concentration of the leaf apoplast and the guard cell symplast, while WP3 will show to which extend the anion composition (NO3−, Cl−) can affect stomatal movements. We will test if guard cells of broad bean and barley prefer NO3−, or Cl−, to accompany the osmotic processes that drive stomatal movements. Finally, WP4 will focus on the role of NPF transporters in the uptake NO3− and Cl− into guard cells and the SLAC1-like anion channels that can release these anions. While SLAC1-like channels have been shown to play a major role in regulation of stomatal movements, only little information is available for uptake of NO3− and Cl− into guard cells by NPF-proteins. The results of our project will help to predict both the impact of progressive soil drying and a reduction of NO3−-N input in soils on transpiration by dicotyledonous and cereal crop plants. In this way, mechanistic information is provided that can be integrated into breeding programs for crops with superb regulatory capabilities for stomatal conductance and water consumption.