Date of Award

Fall 1981

Project Type

Dissertation

Program or Major

Plant Science

Degree Name

Doctor of Philosophy

Abstract

Apical applications of 0.2 micrograms N('6)-benzyladenine (BA), a synthetic cytokinin, or 5 micrograms gibberellic acid (GA) significantly enhanced hypocotyl elongation in intact dwarf watermelon seedlings. Accompanying the increase in hypocotyl length was increased expansion of the cotyledons and inhibition of root growth. A study on dry matter partitioning indicated that both hormones caused a preferential mobilization of metabolites from the cotyledons to the hypocotyl at an expense to roots. However, in comparison to untreated or GA-treated seedlings, BA decreased total translocation of metabolites out of the cotyledons. Hormonal effects on water potential of cotyledons and hypocotyls were determined by allowing organs to equilibrate for 2 h in serial concentrations of polyethylene glycol 4000. Osmotic potentials were determined with a dewpoint microvoltmeter. Results of a time-course study of hormonal effects on water and osmotic potentials indicated that BA stimulated cotyledon expansion and hypocotyl elongation primarily by increasing cell wall extensibility, whereas GA-promotion of cotyledon expansion and hypocotyl growth involved osmoregulation in addition to a lowering of the yielding threshold of the cell wall. Measurements of soluble sugars by a colorimetric procedure and cations by atomic absorption spectrometry confirmed that GA promoted the accumulation of osmotically active solutes in the cotyledons and hypocotyls.

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