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Decline in Energy Reserves of Chlorella sorokiniana upon Exposure to Ozone

Department of Botany and Plant Sciences, University of California, Riverside, California 92521

Ozone exposure has been shown to increase the loss of K from Chlorella cells due to an increase in passive permeability and a depolarization of membrane potential. One factor which likely influences or can be influenced by these changes is the energy state of the cell. To study this relationship, various indicators of cell energy status were examined in the presence and absence of O₃.

The active uptake of chloride and deoxyglucose is nearly completely inhibited by O₃ at a dose at which cellular death, measured by plating efficiency, is minimal. Glucose-stimulated respiration, dependent upon ATP/ADP balance, is depressed to a greater degree than endogenous respiration in ozonated cells. Total ATP and glucose-6-phosphate levels also decrease but not as rapidly, and labeled intermediates of glucose metabolism are lost.

Thus, exposure to O₃ results in a depletion of the cell's energy reserves as substantiated by changes observed in processes which both utilize and generate ATP. This loss in energy reserves occurs at the same exposure level of O₃ as do the changes in passive transport properties. Thus, we cannot tell which occurs first; and the processes seem to be linked with respect to O₃ injury.