Control of Mitochondrial Activities by Phytochrome in Cotyledons of Dark-Grown Cucumber Seedlings

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Abstract
Mitochondria isolated from cotyledons of dark-grown cucumber seedlings after illumination with white light showed an increased capacity for oxidation of malate. This increase is regulated by phytochrome, since the rate of oxidation was increased by brief pulses of red light, the effects of which were reversed by brief pulses of far-red light. Similarly, increases in the rates of oxidation of citrate and α-ketoglutarate were observed in mitochondria isolated from illuminated cotyledons. By contrast, rates of succinate-, exogenous NADH-, durohydroquinone- and ascor-bate-dependent consumption of O2 were little affected by the light treatment. Exogenous NAD+stimulated the oxidation of malate and α-ketoglutarate by mitochondria from dark-grown, control cotyledons, while it did not enhance the rates of oxidation of these substrates by mitochondria isolated from light-treated cotyledons. The activities of mitochondrial enzymes (malate and succinate dehydrogenase, NAD+-malic enzyme and cytochrome oxidase) were not different between illuminated and dark-grown cotyledons. Neither cycloheximide nor chloramphenicol inhibited the increase in the rate of oxidation of malate.

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