Polyphenol production and gene expression in sage shoot cultures exposed to light-emitting diodes.

Sages and their beneficial secondary metabolites have been used in conventional and traditional medicine in many countries, and are extensively studied for their health effects. However, to achieve high production levels, it is crucial to optimize the cultivation conditions. The aim of our study was to determine the optimal light-emitting diode (LED) treatment strategy for promoting plant growth and polyphenol biosynthesis in S. atropatana and S. bulleyana in vitro cultures. Shoots of both species were grown under red, blue, mixed (70 % red and 30 % blue), or white (control) light. The lighting conditions affected not only culture growth and proliferation potential, but also the accumulation of polyphenols and the expression of the genes involved in their biosynthesis (PAL, TAT, RAS). The highest proliferation rates (6.21 for S. atropatana and 4.26 for S. bulleyana) were achieved under white LEDs. In contrast, the highest biomass production was observed under white and mixed red/blue light (both species), although a similar effect was revealed for the blue light treatment for S. bulleyana. The dominant polyphenol in both species was rosmarinic acid: its level was highest in S. atropatana shoots exposed to red light (20.86 mg/g dry weight, DW) and S. bulleyana under white light (19.72 mg/g DW). The effects of the light treatments on gene expression varied between plant species and the analyzed gene; for example, mixed light stimulated RAS expression in S. bulleyana shoots and inhibited it in S. atropatana shoots. Principal component analysis found that gene expression did not always translate directly into rosmarinic acid production. In summary, our findings indicate that optimized lighting conditions have a significant effect on the production of polyphenolic compounds in sage shoot cultures. However, further research is needed to find the relationship between light treatment and plant biosynthetic pathway.