Sycamore suspension cells (Acer pseudoplatanus L.) were grown in the presence of 
sublethal concentrations of copper (50 microM). During the first 5-6 days of 
treatment, growth was not affected, but cell respiration (coupled and uncoupled) 
declined to approximately 60% of its normal value. This decline of respiration 
was attributed to a progressive diminution of the number of mitochondria in 
copper-treated cells, based on the demonstration of the concomitant decline of 
(1) cardiolipin (diphosphatidylglycerol) and cytochrome aa3 (cytochrome 
oxidase), two specific markers of mitochondrial inner membrane, and (2) fumarase 
activity, a specific marker of mitochondrial matrix space. In addition, the 
mitochondria extracted from copper-treated cells presented the same properties 
as those from control cells, concerning substrate oxidation, cardiolipin and 
cytochrome aa3 contents, and fumarase activity. These results strongly suggest 
that copper triggered an arrest of mitochondrial biogenesis, which preceded cell 
division arrest.