Water Transport, Osmotic Adjustment, and Growth of the Vegetative and Reproductive Structures of Maize
Westgate, Mark Edward
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https://hdl.handle.net/2142/71589
Description
Title
Water Transport, Osmotic Adjustment, and Growth of the Vegetative and Reproductive Structures of Maize
Author(s)
Westgate, Mark Edward
Issue Date
1984
Department of Study
Agronomy
Discipline
Agronomy
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Biology, Plant Physiology
Abstract
Evidence from a number of species indicates that plant growing regions exist at water potentials ((PSI)(,w)) lower than those of the water supply. This study was undertaken to determine the nature of this disequilibrium and its relationship to the growth process and osmotic adjustment.
Under conditions favoring rapid expansive growth, a gradient in (PSI)(,w) (approximately 0.4 MPa) occurred in the growing regions of all the vegetative structures of maize (Zea mays L.) decreasing from the transpiration stream to the expanding cells surrounding the xylem. This gradient in (PSI)(,w) was maintained throughout the day by osmotic adjustment in the growing region, but the gradient disappeared as the tissue matured and growth ceased.
When water was withheld from the soil in which the plants were growing, the leaves, stem, roots, and silks exhibited a differential sensitivity to low (PSI)(,w). The maintenance of growth at low (PSI)(,w) was greatest in the roots and was correlated the maintenance of turgor and a favorable gradient in (PSI)(,w) between the expanding cells and the water supply. These observations support the concept that gradients in (PSI)(,w) are required to maintain water flow from the transpiration stream to expanding cells within the growing tissue. They also showed that osmotic adjustment was necessary for both turgor maintenance and gradient maintenance.
The sensitivity of silk elongation to low (PSI)(,w) was greater than that of the leaves and roots and was associated with insufficient solute accumulation to maintain turgor. The level of non-structural carbohydrate in the stem and leaves was low at this time and may have caused the lack of osmotic adjustment in the silks when photosynthesis was inhibited at low (PSI)(,w). Grain fill continued at low (PSI)(,w) and was associated with an increased availability of stored reserves in the stem and leaves later in reproductive development.
When silks grew sufficiently to be exposed at low (PSI)(,w), no grain developed despite hand pollinations. Pollinations made over a range of silk and pollen (PSI)(,w) indicated that this failure of reproduction occurred in the female flowers. The pollen remained viable at extremely low (PSI)(,w) and grain production was independent of pollen (PSI)(,w). Pollen germination, pollen tube growth, or fertilization occurred normally at low (PSI)(,w). However, the development of the embryo, endosperm, and seed coat was inhibited. . . . (Author's abstract exceeds stipulated maximum length. Discontinued here with permission of author.) UMI
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