Resistant xylem from roots to peduncles sustains reproductive water supply after drought-induced cavitation of wheat leaves.

Abstract

Many annual grasses exhibit drought avoiding life cycles where rapid reproduction must be completed before soil water is exhausted. This strategy would seem to require a hydraulic system capable of sustaining reproduction at all costs to the rest of the plant, yet little is known about the whole-plant structure of hydraulic vulnerability in grasses. We examine vulnerability to water-stress induced xylem cavitation in roots, flag leaves, basal and apical regions of peduncles of wheat (Triticum aestivum var Krichauff) to understand the staged failure of xylem function in severe drought. The functionality of segmented vulnerabilities is tested by conducting rehydration experiments after acute dehydration. We show the water supply to peduncles is more drought resistant than in leaves due to greater xylem cavitation resistance, ensuring a pathway of water can be maintained from the roots to the reproductive tissues even after severe water deficit. Differential rehydration of peduncles compared to leaves following drought confirmed the functionality of xylem supply from roots to seed after water stress sufficient to completely cavitate flag leaf vessels. These results demonstrate that a proportion of the hydraulic pathway between roots and seeds remains functional under extreme dehydration, suggesting that vulnerability traits in this key grass species reflect its reproductive strategy.