EFFECTS OF CYCLING TEMPERATURES ON FIBER METABOLISM IN CULTURED COTTON OVULES

The effects of temperature on rates of cellulose synthesis, respiration, and long-term glucose uptake were investigated using cultured cotton ovules (Gossypium hirsutum L. cv Acala SJ1). Ovules were cultured either at constant 34-degrees-C or under cycling temperatures (12 h at 34-degrees-C/12 h at 15-40-degrees-C). Rates of respiration and cellulose synthesis at various temperatures were determined on day 21 during the stage of secondary wall synthesis by feeding cultured ovules with [C-14]glucose. Respiration increased between 18 and approximately 34-degrees-C, then remained constant up to 40-degrees-C. In contrast, the rate of cellulose synthesis increased above 18-degrees-C, reached a plateau between about 28 and 37-degrees-C, and then decreased at 40-degrees-C. Therefore, the optimum temperature for rapid and metabolically efficient cellulose synthesis in Acala SJ1 is near 28-degrees-C. In ovules cycled to 15-degrees-C, respiration recovered to the control rate immediately upon rewarming to 34-degrees-C, but the rate of cellulose synthesis did not fully recover for several hours. These data indicate that cellulose synthesis and respiration respond differently to cool temperatures. The long-term uptake of glucose, which is the carbon source in the culture medium, increased as the low temperature in the cycle increased between 15 and 28-degrees-C. However, glucose uptake did not increase in cultures grown constantly at 34-degrees-C compared to those cycled at 34/28-degrees-C. These observations are consistent with previous observations on the responses of fiber elongation and weight gain to cycling temperatures in vitro and in the field.