Effects of mild night chilling on respiration of expanding cotton leaves.

Utilizing expanding leaves of cotton (Gossypium hirsutum L. cv. Coker 312), the hypothesis that suboptimal night temperatures above those for putative phase transitions of mitochondrial lipids caused greater substrate control of night respiration and increased the control that respiration exerted on ATP-dependent metabolism was tested. Night respiratory CO(2) evolution rates for 5-7-day-old leaves growing at 30/19 degrees (day/night) nearly equaled those of leaves exposed to 28 degrees C nights, while leaves exposed to 15 degrees C nights had rates that were 42% of those at 28 degrees C. No restriction of respiration by carbohydrate supply was detected for leaves grown at either cool night temperature or when warm-grown plants were transferred to cool night conditions. Pyruvate utilization was more sensitive to mild chilling than glycolysis. Growth at 30/19 or 30/15 degrees C resulted in higher nocturnal ATP:ADP and energy charge for expanding leaves than growth at 30/28 degrees C, suggesting a lessening of respiratory control of ATP-dependent metabolism with long-term night chilling. However, cool night exposure resulted in reductions in total phosphorylated adenylates, and the low ATP content, most notably occurring during 15 degrees C nights, may have restricted some metabolic activity. The cause of these low ATP levels and their possible effects on cotton metabolism during chilling remain to be elucidated.