Doctoral Dissertations

Date of Award

6-1987

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Plant, Soil and Environmental Sciences

Major Professor

James M. Stewart

Committee Members

David L. Coffey, John L. Reynolds, Effin T. Graham

Abstract

The ultrastructural distribution of β-glycerophos-phatase (β-GPase) and potassium chloride (KCl) stimulated adenosine triphosphatase (ATPase) activity was investigated in the outer integument of a linted cultivar of cotton, Gossypium hirsutum L. cv. Hancock, and a lintless (naked seed) mutant during differentiation and elongation of cotton fiber. Occurrence of β-GPase activity was investigated from one day preanthesis to three days postanthesis while ATPase activity was studied from one day preanthesis to ten days postanthesis by using a heavy metal simultaneous capture reaction technique. No β-GPase activity was observed in the lintless line or in any controls in the linted cultivar at any stage. In the linted cultivar there was no enzyme activity before anthesis, but as fibers were initiated on the day of anthesis, activity was observed in the expanding fiber cell wall and nucleus. As the fibers started elongating, enzyme activity was particularly concentrated in the cytoplasm and cell wall where directional growth towards the micropyle occurs. By two days postanthesis, β-GPase activity was decreasing in the cell wall and nucleus but was increasing in the nucleolus. Enzyme activity in the nucleolus was highest at three days postanthesis, but nuclear β-GPase activity was not observed then. These results indicate that β-GPase activity was associated with differentiating fiber cells, specifically with those sites where distinct anatomical, and perhaps catabolic, changes were occurring during fiber differentiation. The enzyme activity was not a precursor to, but coincided with, these changes of fiber development. No ATPase activity other than in mitochondria was observed in the lintless mutant. In the linted cultivar no ATP-specific enzyme activity was seen in non-elongating epidermal cells, subepidermal cells of the outer integument or any controls. As fiber initials started elongating, enzyme activity gradually appeared on the tonoplasts of enlarging vacuoles. Heavier lead phosphate deposits were observed on the membrane of small vacuoles compared to the tonoplast. This activity continued at least up to ten days postanthesis. The enzyme inhibitor, N,N-dicyclo-hexylcarbodiimide, inhibited while KCl stimulated tono-plast ATPase activity. The gradual increase of ATPase activity on the tonoplast of expanding fibers, but not on the tonoplast of non-fiber cells, suggest the active transport of osmotically active compounds, presumably potassium (K⁺) and malate, into the vacuoles of expanding fibers. Fusion of smaller vacuoles with the large central vacuole indicates that these structures contribute additional membrane components along with their enzyme activity to the tonoplast of expanding fibers. The occurrence of ATPase activity, of endoplasmic reticulum (ER)-derived vesicular structures, and the organized pattern of deposition of these structures on the tonoplast indicate ER-originated ATPase activity. This study supports the theory of osmoregulation in cotton fiber where ATPase provides the energy for active accumulation of osmotically active compounds (K⁺, malate) into the vacuoles, thereby generating and maintaining the turgor pressure required for fiber expansion.

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