A QUANTITATIVE COMPARISON OF RESPIRATION IN CELLS AND ISOLATED-MITOCHONDRIA FROM PETUNIA-HYBRIDA SUSPENSION-CULTURES - A HIGH-YIELD ISOLATION PROCEDURE

Mitochondria were isolated from small amounts (2-10 g FW) of Petunia hybrida cell suspensions. A high yield was obtained (about 32%) as measured by fumarase activity. The quality of the mitochondria was comparable to that of other plant sources. RC values of about 2.2 could be reached and various substrates were oxidized. The respiration of cells and isolated mitochondria followed the same course during a batch cycle. Like whole cells, mitochondria showed a rapid increase in the capacity of the cytochrome pathway and the CN-resistant, alternative pathway during the first part of the batch cycle, which was followed by a decline. The engagement of the alternative pathway of cells showed the same course in time but was far from complete. In mitochondria, the alternative pathway was fully engaged during the whole batch cycle. Respiration of cells and isolated mitochondria was compared by correcting mitochondrial respiration for yield. In the late logarithmic phase the respiration rate of the cytochrome pathway of mitochondria (in state 3) appeared to be higher than that of cells; in the early logarithmic and stationary phase it was equal. By uncoupling respiration with FCCP it was shown that substrate was not limiting the in vivo respiration during the whole batch cycle, and that ADP was limiting only in the late logarithmic phase. The mechanism by which respiration is adapted to varying growth conditions is discussed.