Transcript levels in plant mitochondria show a tight homeostasis during day and night.

In plants the physiological and biochemical demands on each cell vary greatly between day and night, mostly due to the differing output of photosynthesis. Chloroplasts, the organelles of photosynthesis, are biochemically closely linked to the other energy generating organelles, the mitochondria. We have now investigated whether gene expression in plant mitochondria is influenced by these daily physiological variations. Transcript synthesis in these organelles cycles in a diurnal rhythm, while steady state transcript levels do not vary between light and dark phases and are stable throughout the diurnal (as well as the circadian) time course. This finding suggests that available steady state transcript levels in plant mitochondria are sufficient to provide the required biochemical capacities also at times of peak respiratory and physiological demands.