Photoperiod modulates growth, morphoanatomy, and linalool content in Lippia alba L. (Verbenaceae) cultured in vitro

Interactions between circadian clock regulation and metabolic responses are believed to explain the importance of rhythmic behavior in plant growth and survival. Lippia alba is an important species because of the medicinal properties of its essential oil extract. The objective of this work was to evaluate the effect of photoperiod on anatomy, growth, essential oil profile, and the expression of genes related to the synthesis of monoterpenes, sesquiterpenes, and the circadian clock in L. alba grown in vitro. The plants were cultured in vitro under different photoperiods (4, 8, 16, and 24 h of light) and irradiance of 41 μmol m−2 s−1. After 40 days of culture, results showed that L. alba presented high physiological plasticity under different photoperiods, with improved performance when exposed to continuous light. The best growth; anatomical organization of the mesophyll, stem, roots, and bundles; amount of photosynthetic pigments; photosynthetic rate; and protein synthesis occurred under a photoperiod of 24 h. The biosynthesis of linalool, the major compound, was increased under the 24-h photoperiod, possibly due to reduced geraniol synthesis. These findings allow a better understanding of how photoperiod acts in the regulation of primary and secondary metabolism, and especially with regard to the composition of essential oils.