Influence of light intensity on glandular trichome density, gene expression and essential oil of menthol mint (Mentha arvensis L.)

The effects of 25, 50, 75 and 100% of light intensity (137, 254, 406 and 543 μmol photons m ⁻² second ⁻¹, respectively) on aspects related to volatile synthesis in menthol mint were investigated. Fresh weight production, glandular trichome density and essential oil content showed a significant linear positive correlation with light intensity. Plants under low light intensity (25%) produced an essential oil with high levels of neomenthol, menthol and menthyl acetate. With 50 and 75% of light intensity plants showed an increase in expression of limonene synthase, limonene hydroxylase, (-)-isopiperitenol dehydrogenase, (+)-pulegone reductase and menthol dehydrogenase genes and an anticipation in oil maturity. With 25% of light intensity plants produced an essential oil with the best commercial profile. However, plants under 100% of light intensity produced more essential oil but with lower levels of menthol and higher levels of pulegone, that can be toxic for humans.