Physiological and molecular characterization of cotton (Gossypium hirsutum L.) genotypes in response to water-deficit stress

Water-deficit stress is a major limiting factor in cotton (Gossypium hirsutum L.) production. Three studies were formulated to investigate the responses of the cotton plant to water-deficit stress. The first study questioned the traditionally accepted leaf disk method for assessment of relative water content (RWC). Findings revealed leaf disks absorbed more water than needed to compensate for the original water deficit, thereby jeopardizing the accuracy of the RWC measurement. These studies also showed that overnight rehydration may not be sufficient to fully hydrate a stressed plant.; The effects of foliar applications of the compatible solute, glycine betaine, on the growth and yield of cotton were evaluated in fields studies, and generally had no significant effect on growth parameters, or yield of field grown cotton.; Seven cultivars representative of major US cotton areas were chosen to evaluate the water-deficit stress tolerance of commercial cultivars representing the current germplasm. These included Maxxa (western US), Sphinx (southwest), Fibermax (midsouth), Deltapine Nu33B, Stoneville 747, Sure-Grow 474 (Mississippi River Delta), and Paymaster 1218 (eastern US). An Australian cultivar, Siokra L-23, was included for its known level of drought tolerance. Significant differences in osmotic adjustment were observed among cultivars, and most showed significant increases in photosynthetis three days after stress cessation, especially Siokra L-23 and Sphinx.; Gene expression studies related to proline and trehalose metabolism were conducted via northern analysis using Siokra L-23. Three genes directly involved in trehalose metabolism (trehalose-6-phosphate synthase, trehalose-6-phosphate phosphatase, and trehalase) were up-regulated in response to water-deficit stress. Genes involved in proline synthesis (Δ1-pyrroline-5-carboxylate synthetase and Δ1-pyrroline-5-carboxylate reductase) showed up-regulation during water-deficit stress. Proline dehydrogenase, which breaks down proline, was down-regulated under water-deficit stress conditions.; These investigations suggested methods to improve determination of plant water status, assessed the effects of foliar sprays of glycine betaine, determined responses to water-deficit stress under controlled and field conditions, and evaluated cotton water-deficit stress response at the gene expression level. If agronomic production under adverse environmental conditions is to be improved, knowledge from all areas of plant water-deficit stress must be integrated.