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Insights into the ecophysiological and molecular significance of xylem hydraulic capacitance in Populus under drought stress

Final Report Summary - TREE CAPACITANCE (Insights into the ecophysiological and molecular significance of xylem hydraulic capacitance in Populus under drought stress.)

Global change is expected to amplify the frequency and the severity of heatwaves and drought events that jeopardize tree health and integrity of European temperate forests. Thus, there is a need to identify the processes that may allow trees to overcome severe water scarcities. Although water flow (or hydraulic conductivity) throughout plant tissues plays pivotal roles in drought resistance, there is still a lack of fundamental knowledge on the precise influence of xylem hydraulic capacitance on the buffering of water tension fluctuations.
The objectives of the project were to define the “hydraulic capacity” of xylem water reservoirs under quantified changes in plant water status, and to identify a class of genes that would highlight the functioning of these water storage elements or capacitors, both at molecular and biochemical levels.
This ambitious topic was explored through a multidisciplinary lens. Indeed, ecophysiology (capacitance assessment), molecular biology (expression level and cellular localization of candidate genes coding for capacitance), and biochemistry (functional validation of phosphorylation of some water channels (aquaporins, AQPs) by Wall Associated Kinases, WAKs) were synergized to provide further insight into the capacitance process.
This proposal allowed us to unravel the physical mechanisms of capacitance as a dynamic process during the course of a day in control plants or during water deprivation in several hybrid poplars. The expression analyses showed that both, AQPs and WAKs genes are differentially regulated under changing plant water status. These results are in favor with a “hydromechanosensing” hypothesis were WAKs (bound to the cell wall and to plasma membrane) could sense dehydration at cellular level and then regulate AQPs activity by phosphorylation.
Thus, ecophysiology, molecular biology, and biochemistry provided further insight into the capacitance process as a preventive way to lead with drought stress. Having achieved these objectives will favour environmental protection efforts, with a special emphasis on drought stress, in a context where the optimization of scarce water resources is a major factor. This project provides an opportunity to sustain forest production in European temperate forests and to apply advanced specializations to agronomic objectives of economic interest in Europe.
Finally the results obtained facilitated the launch of a new PhD topic that represents a continuity of the work performed so far. This new project aims at the involvement of midrib in leaf capacitance process.