Confronting Maxwell's demon: biophysics of xylem embolism repair

Embolism results in a dramatic loss of xylem hydraulic transport capacity that can lead to decreased plant productivity and even death. The ability to refill embolized conduits despite the presence of tension in the xylem seems to be widespread, but how this occurs is not known. To promote discussion and future research on this topic, we describe how we believe refilling under tension might take place. Our scenario includes: (i) an osmotic role for low-molecular weight sugars; (ii) an apoplastic sugar-sensing mechanism to activate refilling; (iii) the contribution of vapor transport in both the influx of water and removal of entrapped gases; and (iv) the need for a mechanism that can synchronize reconnection to the transpiration stream through multiple bordered pits.