Chemical inhibition of xylem cellular activity impedes the removal of drought‐induced embolisms in poplar stems – new insights from micro‐CT analysis

Abstract

In drought-stressed plants a coordinated cascade of chemical and transcriptional adjustments occurs at the same time as embolism formation. While these processes do not affect embolism formation during stress, they may prime stems for recovery during rehydration by modifying apoplast pH and increasing sugar concentration in the xylem sap. Here we show that in vivo treatments modifying apoplastic pH (stem infiltration with a pH buffer) or reducing stem metabolic activity (infiltration with sodium vanadate and sodium cyanide; plant exposure to carbon monoxide) can reduce sugar accumulation, thus disrupting or delaying the recovery process. Application of the vanadate treatment (NaVO 3, an inhibitor of many ATPases) completely halted recovery from drought-induced embolism for up to 24 h after re-irrigation, while partial recovery was observed in vivo in control plants using X-ray microcomputed tomography. Our results suggest that stem hydraulic recovery in poplar is a biological, energy-dependent process that coincides with accumulation of sugars in the apoplast during stress. Recovery and damage are spatially coordinated, with embolism formation occurring from the inside out and refilling from the outside in. The outside-in pattern highlights the importance of xylem proximity to the sugars within the phloem to the embolism recovery process.

Shade‐induced reduction of stem nonstructural carbohydrates increases xylem vulnerability to embolism and impedes hydraulic recovery in Populus nigra

“…The shift in xylem vulnerability induced by shading was confirmed by X-ray micro-CT, as the percentage of embolized xylem area (A embol ) at the target Ψ xyl of −1.4 MPa was higher in S than in L plants (Figs 3d,e, S2), that is, 5.1% and 7.3% vs 3.3% and 3.8% (single individual values), respectively. These A embol values are in agreement with those detected in poplar by Secchi et al (2021). Micro-CT scans also confirmed, for well-watered plants (Ψ xyl = −0.3 MPa on average), the presence of residual embolized conduits as inferred from hydraulic VCs (Fig.…”

Testing the limits of plant drought stress and subsequent recovery in four provenances of a widely distributed subtropical tree species

“…Another unresolved aspect of plant drought stress is how tree species restore hydraulic function following drought events (Choat et al, 2018;Klein et al, 2018;Ruehr et al, 2019). It has been reported that some tree species can repair embolized xylem through xylem refilling in a relatively short time (hours) (Ogasa et al, 2013;Secchi et al, 2021), while other species may take much longer (months to years) to restore xylem function via xylem regrowth (Brodribb et al, 2010;Gauthey et al, 2021;Hammond et al, 2019).…”

No Evidence for Light-Induced Embolism Repair in Cut Stems of Drought-Resistant Mediterranean Species under Soaking

“…These controversies can be overcome using X-ray micro-computed tomography (micro-CT), an important tool to visualize embolized xylem conduits at a proper resolution and to quantify in vivo xylem vulnerability, as well as possible hydraulic recovery in intact plants [20,21]. Therefore, this method has been exploited to validate destructive hydraulic methods (e.g., [22,23]) and related sample preparation procedures [24].…”