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Vulnerability of Xylem to Cavitation and Embolism

Vulnerability of Xylem to Cavitation and Embolism WATER RELATIONS AND THE VULNERABLE PIPELINE The evolution of cell walls allowed the plant kingdom to solve the problem of osmoregulation in freshwater environments; confining protoplasm inside a rigid exoskeleton prevented cell rupture as a result of osmotic inflow of water. The cost of cell walls for plants was a loss of motility. In contrast, in the 1040-2519/8910601-0019$02.00 TYREE & SPERRY animal kingdom osmoregulation involved the evolution of a vascular system that bathed most cells in isosmotic blood plasma; this avoided rigid walls and permitted cell and organismal motilty. Cell walls also placed constraints on the evolution of long-distance transport systems. Tissues were too rigid to evolve a heart pump mechanism. Instead plants evolved two novel transport systems. One is a positive pressure system that moves concentrated, sugar rich sap in the phloem from leaves to growing meristems. Phloem transport uses a standing-gradient osmotic flow mechanism similar to that found in some animal excretory organs, but it is unique in that it occurs at very high pressures (up to 3 MPa) and requires two standing-gradient systems in tandem, one of which works in reverse. The other transport system distributes water from the soil throughout the plant via the http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Annual Review of Plant Biology Annual Reviews

Vulnerability of Xylem to Cavitation and Embolism

Tyree, M T; Sperry, J S
Annual Review of Plant Biology , Volume 40 (1) – Jun 1, 1989
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Publisher
Annual Reviews
Copyright
Copyright 1989 Annual Reviews. All rights reserved
Subject
Review Articles
ISSN
1040-2519
DOI
10.1146/annurev.pp.40.060189.000315
Publisher site
See Article on Publisher Site

Abstract

WATER RELATIONS AND THE VULNERABLE PIPELINE The evolution of cell walls allowed the plant kingdom to solve the problem of osmoregulation in freshwater environments; confining protoplasm inside a rigid exoskeleton prevented cell rupture as a result of osmotic inflow of water. The cost of cell walls for plants was a loss of motility. In contrast, in the 1040-2519/8910601-0019$02.00 TYREE & SPERRY animal kingdom osmoregulation involved the evolution of a vascular system that bathed most cells in isosmotic blood plasma; this avoided rigid walls and permitted cell and organismal motilty. Cell walls also placed constraints on the evolution of long-distance transport systems. Tissues were too rigid to evolve a heart pump mechanism. Instead plants evolved two novel transport systems. One is a positive pressure system that moves concentrated, sugar rich sap in the phloem from leaves to growing meristems. Phloem transport uses a standing-gradient osmotic flow mechanism similar to that found in some animal excretory organs, but it is unique in that it occurs at very high pressures (up to 3 MPa) and requires two standing-gradient systems in tandem, one of which works in reverse. The other transport system distributes water from the soil throughout the plant via the

Journal

Annual Review of Plant Biology – Annual Reviews

Published: Jun 1, 1989

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