Micro-CT assisted analysis of xylem recovery from water stress in poplars subjected to chemical inhibition of cellular activity

Perennial plants maintain xylem hydraulic functionality to sustain photosynthetic capacity upon periods of severe drought. Under water stress, plants adjust their xylem pH and gene expression priming stem by accumulation of sugars and ions in the apoplast for xylem functional recovery. Here, we studied if application of ortho-vanadate solution, aimed to inhibit the metabolic activity of wood parenchyma cells and block proton pumps, can affect the xylem sap properties and hinder or delay the recovery process after soil rehydration. Poplar trees were used for in vivo analysis of embolism using X-ray microCT. Despite restoration of water potential, the ortho-vanadate treated rehydrated poplars revealed a significant impediment of in removal of drought-induced embolisms, while control plants showed almost full recovery from embolism. These findings indicate that embolism removal is an energy dependent process that requires accumulation of sugars in the apoplast, while visual observations indicate that process is spatially coordinated, with embolism formation accruing from inside out and recovery from outside in; thus underlining the importance of xylem proximity to phloem (sugar source).