Origin of growth-induced water potential
The authors developed a new method to measure the solute concentration in the apoplast of stem tissue involving pressurizing the roots of intact seedlings (Glycine max (L.) Merr. or Pisum sativum L.), collecting a small amount of exudate from the surface of the stem under saturating humidities, and determining the osmotic potential of the solution with a micro-osmometer capable of measuring small volumes (0.5 microliter). In the elongating region, the apoplast concentrations were very low (equivalent to osmotic potentials of -0.03 to -0.04 megapascal) and negligible compared to the water potential of the apoplast (-0.15 to -0.30 megapascal) measured directly by isopiestic psychrometry in intact plants. Most of the apoplast water potential consisted of a negative pressure that could be measured with a pressure chamber (-0.15 to -0.28 megapascal). Tests showed that earlier methods involving infiltration of intercellular spaces or pressurizing cut segments caused solute to be released to the apoplast and resulted in spuriously high concentrations. These results indicate that, although a small amount of solute is present in the apoplast, the major component is a tension that is part of a growth-induced gradient in water potential in the enlarging tissue. The gradient originates from the extension of the cell walls, which prevents turgor from reaching its maximum and creates a growth-induced water potential that causes water to move from the xylem at a rate that satisfies the rate of enlargement. The magnitude of the gradient implies that growing tissue contains a large resistance to water movement.
- Research Organization:
- Texas A and M Univ., College Station
- DOE Contract Number:
- FG05-84ER13273
- OSTI ID:
- 6473390
- Journal Information:
- Plant Physiol.; (United States), Vol. 83:3
- Country of Publication:
- United States
- Language:
- English
Similar Records
Rapid wall relaxation in elongating tissues. [Glycine max (L. ); Pisum sativum L]
Turgor and growth at low water potentials. [Glycine max (L. ) Merr]
Related Subjects
CELL WALL
PERMEABILITY
SEEDLINGS
PLANT GROWTH
WATER REQUIREMENTS
SOLUTES
ROOT ABSORPTION
GLYCINE HISPIDA
OSMOSIS
PISUM
PLANT STEMS
PRESSURE GRADIENTS
ROOTS
ABSORPTION
BACTERIA
CELL CONSTITUENTS
DIFFUSION
GROWTH
LEGUMINOSAE
MICROORGANISMS
PLANTS
RHIZOBIUM
UPTAKE
551000* - Physiological Systems