The effects of different color lights on the growth, glandular trichome development and essential oil content of Mentha arvensis L

Mentha arvensis L. is well known for producing the monoterpenes menthol; its essential oil (EO) is widely used in pharmaceutics, cosmetics, food and other industries. The peltate glandular trichome (PGT) is the site responsible for the production and storage of EO in mint. Light is one of the most important environmental factors that contributes to plant growth and development, and secondary metabolism. In this report, we have investigated the influence of additional red light (White + Red, W+R) and blue light (White + Blue, W+B) on the parameters of growth, EO, and PGT in M. arvensis. Interestingly, the plant growth parameters, such as the number of branches, plant height, fresh weight, leaf area and number of leaves were significantly greater both under W+R and W+B treatments compared to the control group. Red light proved more beneficial for increasing plant height (by 15.26%) and fresh weight (by 58.42%), whereas blue light was more effective in boosting the number of branches (by 83.68%) and leaves (by 65.07%). The highest increases in essential oil (EO) content (by 36.36%), yield (by 101.72%), and peltate glandular trichome (PGT) density (by 35.64%) were observed under W+B treatment. However, both W+R and W+B had a slightly negative effect on the quality of mint EO, where menthol content decreased by 4.32 per cent and 11.88 per cent respectively. These results proved that red light is more conducive to biomass accumulation, while blue light is more conducive to EO synthesis and PGT development in M. arvensis.