Polymorphic enzyme expression in cold-stressed cotton cultivars

Chilling temperatures during germination and seedling emergence can have devastating effects on seedling cotton Gossypium hirsutum L. stands. Since cotton cultivars differ in their responses to chilling temperatures, one must first identify which enzymes respond to chilling temperatures to use isozyme zymograms to select for chilling tolerance. This research was designed to determine if detectable differences exist in gene expression for enzyme synthesis during germination and if these differences can be used through breeding efforts to increase chilling tolerance in cotton. Seeds of six cotton cultivars were germinated for 6 days at 18°C and 30''C. Radicles were excised and enzymes extracted for separation by starch gel electrophoresis. In addition, radicles were measured daily for growth comparisons at each temperature. Results indicated that Acala 1517-75 germinated and grew better at 18°C than the other five cotton cultivars. These results corresponded to isozyme analysis in which chilling temperatures induced changes in a-amylase, alcohol dehydrogenase, glucose-6-phosphate dehydrogenase, isocitrate dehydrogenase, and malate dehydrogenase. Isozyme staining intensity, indicative of specific isozyme activity, was greatest at 18°C for alcohol, glucose- 6-phosphate, isocitrate, and malate dehydrogenases. Although no one dehydrogenase was found to be an exclusive indicator of cold tolerance, it is anticipated that with further experimentation a genetic marker isozyme can be identified for use in breeding efforts to increase chilling tolerance in Upland cotton.