The effects of cool night temperatures on respiration and growth of immature cotton (Gossypium hirsutum L. cv.Coker 312) leaves
Cogburn, Carolyn Joy
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The aim of this study was to determine the effects of cool night temperatures on respiration, its substrate, and growth of immature leaves of cotton. Plants grown at both 30/19 and 30/15° C (day/night) had fewer primary and axillary leaves, fewer flower buds, and were shorter than plants grown at 30/28° C. However, rates of leaf expansion and dark respiration of immature leaves of plants grown at 30/19° C were maintained at levels near those of plants grown at 30/28° C while 30/15° C conditions caused reduced rates of leaf expansion and dark respiration. Transferring plants grown at 30/28 to 30/19° C caused a reduction in leaf respiration rates and hexose content, but with time, rates of respiration and hexose content retumed to those values of leaves grown at 30/28°C. Elevated pymvate levels indicated that the initial reduction in hexose was not restricting glycolysis relative to downstream reactions. Transfer from 30/28 to 30/15° C resulted in a similar decrease in dark respiration rates during the first cool night, but hexose content was unchanged and rates of respiration did not recover with time. The immature leaves of warm-grown plants transferred to 30/19° C did exhibit a slight decrease in ATP/ADP ratio during the first cool night. Thus, the slow rates of respiration that first cool night were not able to meet the demand for ATP in the short term. However, for leaves of plants transferred to 15° C or in the long-term at 15 or 19° C, the percentage of adenylates as ATP was higher than for leaves of plants at 30/28° C. Thus, respiratory production of ATP was greater than ATP utilization and was not likely to restrict growth processes.