RESPONSE OF CARBON METABOLISM TO NIGHT TEMPERATURE IN COTTON

Cotton (Gossypium hirsutum L.) is sensitive to low temperatures during all phases of growth. Throughout the cotton growing season on the Hig h Plains of Texas, days provide optimal sunlight and temperature for m etabolism followed by nights with temperatures of 15 to 20 degrees C, well below the optimum. The present growth chamber study compared the response of specific components of C metabolism in vegetative cotton g rown with 28 degrees C/28 degrees C and 28 degrees C/20 degrees C day/ night regimes. Photosynthesis for cool-night (20 degrees C) plants mea sured at 28 degrees C the following day was only 77% of 28 degrees C n ight plants, Less starch accumulation occurred during the day in the c ool-night plants, yet their predawn starch levels were approximately 2 .5-fold higher than the 28 degrees C plants. Pools of triose phosphate and fructose 1,6-bisphosphate were lower at night at 20 degrees C tha n at 28 degrees C. The glucose 6-phosphate/fructose 6-phosphate ratio was higher for the cool-night plants, however, indicative of an appare nt limitation in sucrose synthesis subsequent to cytosolic fructose 1, 6-bisphosphatase. The most interesting observation is the maintenance of equal sucrose pools in both treatments, even though the amount of s tarch catabolized at night was different. This study shows that cool n ight temperatures alone alter cotton C metabolism throughout each 24-h period.