LEAF RESPIRATION AND ATP LEVELS AT CHILLING TEMPERATURES

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Abstract
SUMMARY: In the extremely chill‐sensitive species Episcia reptans the dark respiration rate of leaves after 80 min chilling at 5°C was three times greater than in leaves maintained at 25°C. The rate and size of the respiratory increase depended on the chilling temperature and the growth conditions prior to chilling and was at a maximum at the same time as the onset of visible injury. The addition of 2,4‐dinitrophenol and potassium cyanide to the leaves of E. reptans accelerated the rate of oxygen uptake at 5°C. In contrast, there was no increase in the respiration rate of the leaves of the less chill‐sensitive species Phaseolus vulgaris after prolonged chilling at 5°C.A reduction in ATP supply below that necessary to maintain the metabolic integrity of the cytoplasm is not considered to be important in the development of chilling‐injury to Episcia reptans or Phaseolus vulgaris as the ATP level decreased only after the onset of visible leaf injury. Furthermore, the increase in ATP level on chilling P. vulgaris leaves which had been either chill‐hardened or maintained in a saturated atmosphere on transfer from 25 to 5°C (Wilson, 1976) demonstrated that leaf injury and water stress are the primary cause of the decline in ATP level during chilling and not low temperature per se.