Diel variation of sesquiterpene elatol production: a chemical defense mechanism of the red seaweed Laurencia dendroidea

• Diel variation in secondary metabolite production of the seaweed Laurencia dendroidea was investigated.
• Inverse correlation between primary (photosynthesis) and secondary (elatol production) metabolisms is reported.
• Importance of natural habitat, genetic variability and endogenous control on chemical defense production is discussed.

Variability in the production of secondary metabolites by seaweeds is commonly measured under natural conditions and is usually considered a response to environmental factors. However, it is not well known if levels of secondary metabolites can vary due to internal regulation of physiological processes. We measured the diel levels of elatol - the major defensive compound of Laurencia dendroidea - in correlation with the activity of photosystem II (ΦPSII) in clones of this seaweed cultivated under constant conditions of temperature, salinity, nutrient availability and irradiance. Our results showed temporal variation in amounts of elatol, which peaked at the beginning of the light and dark periods. The ΦPSII during the light phase, as measured by chlorophyll fluorescence imaging, was higher when the elatol concentration was lower. We conclude that under constant conditions, i.e. without the influence of natural habitat and genetic variability, there is diel variation in elatol production that is inversely correlated with ΦPSII. We suggest that both metabolic activity of secondary metabolite production and photosynthetic activity are under an endogenous control in this red seaweed. We discuss the possible adaptive responses of this phenomenon to environmental pressures.