Physiological drought stress imprints related to root exudation in the rhizosphere

在中欧，由于气候变化，预计短暂的干旱会增加。所谓的“应激印记”描述了植物在应激事件后发生的变化，以及对随后的应激反应的改善。这种修改是本项目的重点。根系分泌物在干旱胁迫下发生改变，有利于根系在干燥土壤中生长，但根系分泌物是否在根际发生与根系分泌物相关的生理干旱胁迫印记，根系分泌物的时空格局对胁迫程度、持续时间和胁迫发生类型的响应仍然是一个悬而未决的问题。(3)根系在干旱条件下的代谢重组如何影响胁迫后植物的抗逆性和养分吸收性能。该项目提出了四个假设：(1)生理干旱胁迫印记发生在根际，并由根渗出物的改变介导；(2)这些印记的程度取决于干旱事件发生的速度、严重程度和持续时间，以及随之而来的对光系统的破坏；(3)这些印记导致资源向根系的时空再分配；(4)它们影响胁迫后植物在水分和养分吸收方面的表现。在这个项目中，植物暴露于不同的干旱胁迫类型，包括不同的强度、持续时间和进展速度。通过收集渗出物来确定渗出物的产量，并通过LC-MS分析来评估其成分。在干旱过程中监测光合作用相关过程，并通过叶绿素荧光和生化胁迫标志物评估光系统受到的损害。通过对复浇过程中应力印迹的时间过程分析，确定了应力印迹的持久性。在根箱中，一半的根暴露在单一的干旱中，另一半暴露在反复的干旱中。利用蛋白质组学方法，收集了两半根的根分泌物，并监测了整个植物的代谢重组以及两半根之间的代谢串扰。通过评估植物水分关系的恢复时间和营养物质的吸收，辅以水通道蛋白和选定的营养转运体的表达研究，分析胁迫后植物的表现。盆栽试验与田间从根窗收集的类似渗出物分析相辅相成。这些研究的结果将为干旱诱导的地上光合过程的变化及其在根渗出物变化介导的地下根际过程的持久印记之间的时空相互作用提供信息。它们有助于获得对系统根/茎潜在代谢反应的机制理解，这可能导致干旱后次优生长条件下胁迫后性能的改善。

In Central Europe, transient drought spells are predicted to increase due to climate change. So-called “stress imprints” describe modifications in plants that occur after a stress event and improved responses to subsequent stresses. Such modifications are in the focus of this project. Root exudates are altered under drought stress to facilitate root growth into the drying soil, but it remains an open question (i) whether physiological drought stress imprints related to root exudation occur in the rhizophere, (ii) in which spatio-temporal pattern root exudation responds to stress severity, duration and stress onset type, and (iii) how metabolic re-organization of the root system in response to drought affects post-stress plant performance with respect to stress resilience and nutrient uptake.This project addresses four hypotheses: (1) physiological drought stress imprints occur in the rhizosphere and are mediated by altered root exudation; (2) the extent of these imprints depends on the speed of onset, severity and duration of the drought event and concomittant damage to the photosystem; (3) these imprints lead to spatio-temporal re-distribution of resources towards the root and (4) they affect post-stress plant performance with respect to water and nutrient uptake. In this project, plants are exposed to different drought stress types including different intensities, durations and speeds of progression. Exudate production is determined by collecting exudates and composition is assessed by LC-MS analyses. Photosynthesis-related processes are monitored during the progression of drought, and damage to the photosystem is assessed by chlorophyll fluorescence and biochemical stress markers. The persistence of the stress imprints is determined by time course analysis during re-watering. In a rhizobox setup, one half of the roots is exposed to a single, and one half to recurrent drought drought spells. Root exudates are collected from both root halves and metabolic reorganisation of the whole plant as well as metabolic crosstalk between the root halves is monitored using a proteomic approach. Post stress plant performance is analysed by assessing the recovery time for water relations in the plant and uptake of nutrients, complemented by expression studies of aquaporins and selected nutrient transporters. The pot experiments are complemented by similar analyses of exudates collected from root windows in the field.The outcomes of these studies will provide information on the spatio-temporal interplay between drought-induced changes in photosynthetic processes aboveground, and their lasting imprints on rhizosphere-based processes belowground, mediated by alterations in root exudates. They help to gain a mechanistic understanding of underlying metabolic responses of the system root/shoot which may lead to an improved post-stress performance under conditions of sub-optimum growth conditions after drought.