Interplay of Circadian Rhythms and Light in the Regulation of Photosynthesis-Derived Metabolism

Alternating periods of day and night confer an environmental rhythm upon terrestrial plants. Seasonal changes in light intensity and duration (as well as integrals of temperature) inform developmental decisions that directly impact upon plant growth. In response to the selective pressure of these daily rhythms, plants have evolved an endogenous, biological oscillator that coincides with these patterns. These circadian rhythms allow plants to anticipate daily transitions and consequently allocate specific metabolic functions to certain times of day. The circadian system also has a dramatic effect upon development, with the external coincidence model describing how plants measure day length to induce flowering under inductive conditions. Plants? responses to environmental change are therefore a distillation of direct responses to abiotic factors and moderating factors derived from endogenous biological rhythms. This review summarizes our understanding of how metabolic processes are governed by these interactions, with particular attention to carbon and redox metabolism, two processes derived from photosynthesis.