Bioenergetics of tomato (Lycopersicon esculentum) development on the plant was followed from the early growing stage to senescence in wild type (climacteric) and nonripening mutant (nor, non-climacteric) fruits. Fruit development was expressed in terms of evolution of chlorophyll a content allowing the assessment of a continuous time-course in both cultivars. Measured parameters: the cytochrome pathway-dependent respiration, i.e., the ATP synthesis-sustained respiration (energy-conserving), the uncoupling protein (UCP) activity-sustained respiration (energy-dissipating), the alternative oxidase(AOX)-mediated respiration (energy-dissipating), as well as the protein expression of UCP and AOX, and free fatty acid content exhibited different evolution patterns in the wild type and nor mutant that can be attributed to their climacteric/nonclimacteric properties, respectively. In the wild type, the climacteric respiratory burst observed in vitro depended totally on an increse in the cytochrome pathway activity sustained by ATP synthesis, while the second respiratory rise during the ripening stage was linked to a strong increase in AOX activity accompanied by an overexpression of AOX protein. In wild type mitochondria, the 10-microM linoleic acid-stimulated UCP-activity-dependent respiration remained constant during the whole fruit development except in senescence where general respiratory decay was observed.