Date of Graduation

7-2015

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Crop, Soil & Environmental Sciences (PhD)

Degree Level

Graduate

Department

Crop, Soil & Environmental Sciences

Advisor

Derrick M. Oosterhuis

Committee Member

Fred M. Bourland

Second Committee Member

Curt R. Rom

Third Committee Member

Leo Espinoza

Fourth Committee Member

Glen R. Ritchie

Keywords

Biological sciences

Abstract

Drought stress is one of the major abiotic factors affecting crop growth and limiting production worldwide. Cotton genotypes vary in drought tolerance, and the effects of drought stress on the anatomy and physiology of cotton leaves and roots have been reported. However, information on physiological and metabolic processes of leaves and flowers of modern cotton cultivars under water-deficit stress during reproductive development is not well elucidated. It was hypothesized that water-deficit stress during squaring and flowering stages would impair stomatal conductance and photosynthetic efficiency of leaves, which consequently would result in osmotic adjustment through accumulation of compatible solutes, increased activity of enzymes, and perturbation of carbohydrates metabolism in leaves and flowers of cotton plants, and differences in drought tolerance among the genotypes would exist. Therefore, field and growth room experiments were conducted to evaluate the effects of water-deficit stress during reproductive development on the physiology and metabolism of leaves and flowers of a diverse range of cotton genotypes. Results indicated that water-deficit stress significantly decreased stomatal conductance of cotton plants. Water-deficit stress during the early squaring stage increased activity of antioxidant enzymes, and decreased photosynthetic efficiency and concentrations of pigments of cotton leaves. Carbohydrate metabolism in cotton flowers and subtending leaves was also compromised by water-deficit conditions, with a shift in the carbohydrate partitioning being promoted by the stress, with subtending leaves and bracts as main sources and pistils as main sinks, mainly for sucrose and soluble sugars. In addition, osmotic adjustment through proline accumulation and changes in osmotic potential is a mechanism used by cotton plants to tolerate drought stress. Leaves are more sensitive to water-deficit stress than ovaries, thus with higher osmotic adjustment. Finally, genotypes varied in tolerance to drought, with genotypes that showed higher osmotic adjustment in leaves and flowers indicating higher tolerance to drought episodes. Osmotic adjustment through accumulation of compatible solutes could be used as an effective tool for drought-tolerant genotypes in plant biotechnology. However, further research is needed for complete elucidation of osmotic adjustment and carbohydrate metabolism in flower tissues of cotton genotypes under drought conditions during the flower development.

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