Inhibition of xylem cellular activity blocks recovery from drought induced embolism in poplar – insights from micro-CT analysis.

Perennial plants affected by drought-induced embolisms may benefit from mechanisms allowing for fast recovery of lost xylem hydraulic capacity to reduce prolonged impact on photosynthetic activity upon rehydration. Recent findings suggest that under water stress, a coordinated cascade of chemical and transcriptional adjustments occurs during stress. These processes while not changing xylem embolism level effectively prime stem for recovery by accumulation of sugars and ions in the apoplast. In this study, we test if chemical treatments either affecting stem pH (in vivo infiltration of xylem with pH buffer) or stem metabolic activity (xylem infiltration with NaVO3, NaCN, or plant exposure to CO gas), can reduce sugar accumulation, thus hindering or delaying recovery during rehydration. The ortho-vanadate treatment (NaVO3), aimed to block proton transporters and ATP metabolism, was selected for visual, in vivo analysis of embolism recovery using X-ray-microCT in comparison to untreated plants. Application of NaVO3 led to an impediment in removal of embolisms formed during drought, despite the full recovery of leaf hydration to pre-stress conditions, while almost full removal of embolism was observed in control plants. Results suggest that embolism removal is an energy dependent process that requires accumulation of sugars in the apoplast. Image analyses indicated that the recovery 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 (carbohydrates source)