Abstract: A field trial with high fiber quality cotton cultivar Kemian 1 was conducted in Nanjing (lower reaches of Yangtze Rive) in 2006-2007 to study the effects of growth regulators 6-BA and ABA on the boll and fiber development and related physiological mechanisms under low temperature stress. The cotton seeds were sown on April 25 and May 25, respectively, which could result in different temperature for the bolls on the same positions, and the growth regulators were sprayed at flowering stage. Spraying 6-BA increased the boll weight and fiber quality under both normal and low temperature conditions; whereas spraying ABA induced the decrease of fiber quality under normal temperature but decreased the reduction magnitude of fiber quality under low temperature condition. 6-BA increased significantly the boll sucrose content and sucrose synthase and sucrose phosphate synthase activities, while ABA only increased boll β-1,3-glucanase activity. Both 6-BA and ABA had less effects on the activity of sucrose invertase, a key enzyme for fiber development. Under low temperature condition, spraying 6-BA or ABA improved fiber quality, but the action mechanisms were different. 6-BA improved fiber quality via enhancing the activities of relevant enzymes; while ABA improved fiber quality via increasing the stress resistance of cotton plants.

Key words: cotton, fiber, low temperature, 6-BA, ABA, enzyme activity