Physiological drought stress imprints related to root exudation in the rhizosphere

在中欧，由于气候变化，预计短暂的干旱时间将会增加。所谓的“胁迫印记”描述了植物在胁迫事件后发生的改变，以及对随后的胁迫反应的改善。这样的修改是本项目的重点。根分泌物在干旱胁迫下发生改变，以促进根生长到干燥的土壤中，但(I)根际是否存在与根分泌物相关的生理干旱胁迫印记，(Ii)根分泌物响应胁迫严重程度、持续时间和胁迫类型的时空模式，以及(Iii)干旱响应下的根系代谢重组如何影响胁迫后植物在胁迫恢复和养分吸收方面的表现。本研究提出了四个假设：(1)生理干旱胁迫印记发生在根际，并由改变的根分泌物介导；(2)这些印记的程度取决于干旱事件的发生速度、严重程度和持续时间以及伴随而来的对光系统的损害；(3)这些印记导致资源向根的时空重新分配；(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，植物暴露在不同的干旱胁迫类型中，包括不同的强度、持续时间和进展速度。渗出物的产生通过收集渗出物来确定，成分通过LC-MS分析来评估。在干旱过程中监测光合作用相关的过程，并通过叶绿素荧光和生化胁迫标记来评估对光系统的损害。应力印记的持久性由重新浇水过程中的时间历程分析确定。在根箱中，一半的根暴露在一次干旱中，另一半暴露在反复的干旱中。根分泌物是从根的一半和整个植物的代谢重组中收集的，根一半之间的代谢串扰是用蛋白质组学的方法监测的。通过评估植物中水分关系和养分吸收的恢复时间来分析胁迫后的植物表现，并辅之以水通道蛋白和选定的营养转运蛋白的表达研究。盆栽试验的补充是对田间根窗分泌物的类似分析。这些研究的结果将提供干旱引起的地上光合作用过程的变化及其在地下根际过程中的持久印记之间的时空相互作用信息。它们有助于从机制上了解根冠系统的潜在代谢反应，这可能导致在干旱后次优生长条件下改善胁迫后的表现。

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.