Control by photoperiodism of glycolysis and the connected “Crassulacean Acid Metabolism”; pathway in the leaves ofKalanchoe blossfeldianais shown to achieve strict coordination between the two pathways, and more particularly between their key‐enrymes (phosphofructokinase and phosphoenolpyruvate carboxylase) with respect both to seasonal and day‐night variations. After transfer from long days to short days, increases in the catalytic capacity of the enzymes and the size of metabolite pools follow similar kinetics. These changes are accompanied by coherent phaseshiits in the day‐night rhythms of metabolite concentration and of enzyme capacity. The results suggest that rapid readjustments of functions seem to be involved in the entrainment of enzyme rhythms by lights‐off.