Plant uncoupling mitochondrial protein activity in mitochondria isolated from tomatoes at different stages of ripening

In the present study we have observed a higher state of coupling in respiri ng mitochondria isolated from green as compared to red tomatoes (Lycopersic on esculentum, Mill.). Green tomato mitochondria produced a membrane potent ial (Delta Psi) high enough to phosphorylate ADP whereas in red tomato mito chondria, BSA and ATP were required to restore Delta Psi to the level of th at obtained with green tomato mitochondria. This supports the notion that s uch uncoupling in red tomato mitochondria is mediated by a plant uncoupling mitochondrial protein (PUMP; cf, Vercesi et al., 1995). Nevertheless, mito chondria from both green and red tomatoes exhibited an ATP-sensitive linole ic acid (LA)-induced Delta Psi decrease providing evidence that PUMP is als o present in green tomatoes. Indeed, proteoliposomes containing reconstitut ed green or red tomato PUMP showed LA uniport and LA-induced H+ transport. It is suggested that the higher concentration of free fatty acids (PUMP sub strates) in red tomatoes could explain the lower coupling state in mitochon dria isolated from these fruits.