An emerging theory contends that chilling injury is due to oxidative damage resulting from the metabolic generation of active oxygen species. Mitochondria were isolated from chilling-sensitive (CS) and from conditioned chilling-resistant (CR) bell pepper fruit and their ability to generate superoxide determined by measuring the formation of adrenochrome from epinephrine. Mitochondria from CS fruit were sensitive to cyanide and produced superoxide when supplied with NADH, succinate, or malate-pyruvate. Mitochondria from CR fruit were insensitive to cyanide and sensitive to SHAM and produced little superoxide when supplied with respiratory substrates. ATP enhanced the production of superoxide and ADP reduced the production. Results suggest that the mitochondria are a major source of superoxide in CS plant tissue and the presence of the alternative pathway reduces the production of superoxide.
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