Only a matter of time: the impact of daily and seasonal rhythms on phytochemicals

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Plants regulate molecular bioactivity in response to daily and seasonal environmental fluctuations in temperature, light, humidity, and precipitation. These rhythms interconnect, overlap, and feedback both into each other and into the plant’s endogenous circadian clock. The resulting regulatory network tightly ensures that the overall phytochemical composition is highly adaptive to the plant’s needs at any point in time. Temporally coordinated control of primary and secondary metabolism ensures phytochemicals are in tune with the demands of the environment and the available resources. As a consequence, phytochemical composition varies throughout the day and year. This variation in phytochemical abundance and composition across time can affect experimental results and conclusions. Understanding how phytochemical composition varies across time is critical for uncovering the underlying regulatory connections and ultimately improving the quality of phytochemical products. Herein, we review the mechanisms underlying diel and seasonal variations in phytochemical composition and provide examples of temporal regulation of specific compounds within phenol, terpenoid, and alkaloid phytochemical classes. Temporal regulation of phytochemical composition. The phytochemical composition of a plant is under complex control, affected by both external environmental factors and endogenous circadian rhythms. The environmental factors that directly affect phytochemical profiles and concentrations themselves vary across time of day and time of year. These cyclic environmental factors also entrain the endogenous circadian clock which imposes additional regulation on the production and processing of many phytochemicals. This concerted effort to ensure phytochemicals are exquisitely in tune with the demands of the environment results in fluctuating phytochemical composition. Variation in phytochemical abundance and composition across time can affect experimental results and conclusions. Failing to consider the factors of time of day and year can result in misleading or inconsistent estimations of the potency and composition of phytochemical extractions. Integrating temporal factors will improve our understanding of the underlying regulatory connections and ultimately improve the quality of phytochemical products.