Cool temperature-induced changes in metabolism related to cellulose synthesis in cotton fibers
Martin, Laual Kirt
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Fiber secondary wall thickening associated with cellulose synthesis in cotton (Gossypium hirsutum L.) is greatly hindered under the cool night temperatures that occur during the growing season on the Southem High Plains of West Texas. Fibers on cultured cotton ovules exposed to a 34/15°C temperature cycle during secondary wall synthesis were used as an experimental system to investigate the biochemical causes of this hindrance. Pool sizes of the metabolites related to cellulose synthesis were measured at cool temperature (15°C) and at the optimum temperature for fiber cellulose synthesis (34°C) in the fibers of cultured ovules from seven cultivars. Glucose 6-phosphate levels increased during the 15°C part of the temperature cycle, with 40- 70% increases observed in all cultivars compared to 34°C. Partially cooltolerant cultivars (such as Paymaster HS2(X)) demonstrated the ability to increase glucose 6-phosphate levels greatly at 15°C on the first day of exposure to cycling temperature; however, more cool-sensitive cultivars (such as Acala SJ-1) did not demonstrate this ability until 6 days after the cycling temperature commenced. Fmctose 6-phosphate levels at 15°C within the fiber gradually increased above that at 34°C during the 6 days of cycling. UDP-Glucose levels decreased or only slightly increased at 15°C during the 6 days of cycling, although glucose 6-phosphate levels increased dramatically. Therefore, a possible enzymic restriction at cool temperatures may occur subsequent to glucose 6-phosphate in the cellulose synthesis pathway. Pulse/chase studies supported the hypothesis of an enzymic restriction subsequent to glucose 6-phosphate, with partially cool-tolerant Paymaster HS200 showing less restriction than more cool-sensitive Acala SJ-1.