Oxidative Stress is Generated Via the Mitochondrial Respiratory Chain during Plant Cell Apoptosis

Abstract

Background: We present evidence that in plant cells DNA damage induced by the topoisomerase trapping drug camptothecin induces oxidative stress via the mitochondrial respiratory chain. Methods: Flow cytometry was used to analyse mitochondrial respiratory chain activity by simultaneous measurement of mitochondrial generation of reactive oxygen intermediates (ROI) and mitochondrial membrane potential (Δψm), in live functioning sugarbeet protoplasts. The mitochondrial respiratory chain function was assessed by the addition of substrate and inhibitors to the digitonin-permeabilised protoplasts. Mitochondrial activity was also measured in protoplasts at different stages of induced apoptosis by camptothecin. Results: The addition of camptothecin to sugarbeet protoplasts resulted in increased mitochondrial generation of ROI, occurring concurrently with the hyperpolarisation of the mitochondrial inner membrane. Subsequently, there was a decrease in mitochondrial-generated ROI, in association with a decrease in Δψm. These camptothecin-treated digitonin-permeabilised protoplasts could be re-energised and ROI decreased by the addition of malic acid in the early stages of apoptosis induction, but not in the latter stages. There was a depolarisation of the mitochondrial inner membrane in the final stages of apoptosis. Conclusions: These results are consistent with impaired adenine nucleotide exchange across the mitochondrial membrane, suggesting that similar mechanisms regulate plant apoptosis as those described for mammalian apoptosis. © 2003 Wiley-Liss, Inc.