CONSERVATION OF THE ALTERNATIVE OXIDASE AND ENHANCEMENT OF CYANIDE-RESISTANT RESPIRATION IN SUSPENSION-CULTURED PEAR FRUIT CELLS BY INHIBITORS OF MACROMOLECULAR-SYNTHESIS

The contribution of the alternative pathway to the respiration of susp ension-cultured pear (Pyrus communis cv. Passa Crasanne) cells was enh anced, often severalfold, within 2 to 4 days following the addition of cycloheximide, actinomycin D, or 2-(4-methyl-2,6-dinitroanalino)-N-me thyl propionamide (D-MDMP). Concomitant inhibition of cellular protein synthesis by cycloheximide and actinomycin D was transient and incomp lete. However, inhibition by D-MDMP was virtually complete (>97%) and persisted over several days. [S-35]-labelling and polyacrylamide gel s eparation indicated that cycloheximide precluded the appearance of dis cernable new proteins in mitochondria. Probes with monoclonal antibodi es revealed a conservation of alternative oxidase protein levels in th e mitochondria of inhibitor-treated cells. The data, appraised within the complexities of cell-culture dynamics, lead to the conclusion that the observed increases in capacity for cyanide-resistant respiration are the consequence, likely indirect, of inhibited protein synthesis w ith resultant retention and activation of constitutive alternative oxi dase.