CAN CELL-WALLS BENDING ROUND XYLEM VESSELS CONTROL WATER-FLOW

Vascular bundles of petioles below wilted leaves of Nymphoides peltata (S.G. Gmel. O. Kuntze) were frozen intact and freeze-fractured for EM. Cell walls in them appeared drawn in against the helical thickenings of xylem vessels. By contrast, walls round vessels which were frozen in vascular bundles below turgid leaves, and walls round vessels which were fixed, embedded and sectioned, were straight or bulged outwards slightly. Walls bulged outwards slightly also from cut vessels filled with sucrose solution before freezing. Movement of vessel walls could produce the clicks audible when water cavitates in vessels, and might explain a variable resistance to the flow of water through plants.