Phytochrome-driven changes in respiratory electron transport partitioning in soybean (Glycine max. L.) cotyledons.

After it was observed that light induces changes in electron partitioning between the cytochrome and the alternative pathway, the focus interest was directed to assessing what type of photoreceptors are involved and the extent of such modifications. Studies on 5-day-old soybean (Glycine max L.) cotyledons using an oxygen isotope fractionation technique showed that phytochrome is involved in changes in electron partitioning between the cytochrome and the alternative respiratory pathway. A follow-up of a previous study, showing that 5 min of white light caused changes in mitochondrial electron partitioning, demonstrated that while blue light was not involved in any such changes, red light caused a significant shift of electrons toward the alternative pathway. The major shift, observed after 24 h of light, is mainly due to both a decrease in the activity of the cytochrome pathway and an increase in the activity of the alternative pathway. The involvement of a phytochrome receptor was confirmed by demonstration of reversibility by far-red light. The implications of the possible involvement of phytochrome in the regulation of mitochondrial electron transport are discussed.