Control of mitochondrial activities by phytochrome during greening.

Mitochondria isolated from 7-day old darkgrown Avena sativa L. (var. Arnold) laminae given 5 min illumination of red light, followed by varying lengths of darkness up to 3 h, showed at least a twofold increase in the rates of both NADH-dependent oxygen consumption and respiratory chain phosphorylation over those of mitochondria isolated from unilluminated tissue. Similar organelles, isolated from tissue given either far-red or red followed by far-red pretreatment, exhibited rates of both functions of between 25% and 75% below those of the mitochondria from unilluminated tissue. The induction-reversion criteria for phytochrome control of respiration and oxidative phosphorylation were satisfied under all experimental conditions during the greening process.Treatment with continuous far-red light, acting presumably through the 'high irradiance' reaction of phytochrome, served to disengage phytochrome activity from photosynthesis. The stimulation of oxidative phosphorylation still occurred under these conditions, slightly slower but much more prolonged in the absence of ATP from photophosphorylation.