Mechanism of Cell Enlargement at Low Water Potentials (growth-Induced, Turgor, Hydraulic Conductance, Wall)
Nonami, Hiroshi
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https://hdl.handle.net/2142/71284
Description
Title
Mechanism of Cell Enlargement at Low Water Potentials (growth-Induced, Turgor, Hydraulic Conductance, Wall)
Author(s)
Nonami, Hiroshi
Issue Date
1986
Department of Study
Plant Biology
Discipline
Plant Biology
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Biology, Plant Physiology
Abstract
Cell enlargement in plants is often inhibited at low water potentials (low (psi)(,w)), but the cause is not completely understood. This work was conducted to identify the primary signal(s) that initiate the inhibition and the factors controlling rates of enlargement at low (psi)(,w).
Soybean (Glycine max (L.) Merr.) seedlings were grown in the dark at saturating humidities to assure that the only water transport was for growth. Measurements in the enlarging tissue of the stems with the isopiestic psychrometer, pressure probe, and pressure chamber showed that neither turgor loss nor high solute concentrations due to osmotic adjustment caused the inhibition of cell enlargement at low (psi)(,w). However, the (psi)(,w) in the enlarging cells formed a potential field in the tissues that created a gradient in (psi)(,w) and supplied water to the enlarging cells. This growth-induced (psi)(,w) field was disrupted at low (psi)(,w), which correlated with the growth inhibition. Growth recovered if the growth-induced (psi)(,w) field was quickly reestablished. However, after 10 to 20 h at low (psi)(,w), decreases of wall extensibility and tissue conductance for water occurred. In this case, the recovery of growth required not only a recovery of the (psi)(,w) field but also a recovery of wall extensibility and tissue conductance. Thus, the primary signal triggering the growth response was the change in the (psi)(,w) field, but this was followed secondarily by metabolic modifications that reduced the ability of the cells to grow. This concept explained the differential sensitivity of root and stem growth to low (psi)(,w). Tests showed that the (psi)(,w) field formed primarily because of the frictional properties for water movement through the enlarging tissue and not because of solute in the apoplast.
A comparison was made of stem osmotic adjustment and root and shoot growth in a range of species and genotypes. All genotypes adjusted osmotically and showed turgor maintenance similar to that of soybean. Genotypes that were insensitive to or lacking gibberellic acid or abscisic acid were capable of osmotic adjustment and turgor maintenance.
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