Photoreceptor regulation of Hypericum perforatum L. (cv. Topas) flowering under different light spectrums in the controlled environment system

The content of secondary metabolites in medicinal plants is affected by several internal and external stimuli. Light quality is regarded as one of the considerable environmental factors affecting plant photomorphogenesis processes and bio-active compounds biosynthesis. There is a great demand for high-quality medicinal plants and plant factory systems would be helpful in response to this demand. But, before using these systems, the light spectrum required for each species must be determined. So, in this study the Hypericum perforatum L. cv. Topas plantlets were subjected to six red (R) to blue (B) light ratio treatments including 100 R:0B, 80 R:20B, 50 R:50B, 20 R:80B, 0 R:100B, and white LED was considered as control. Among the six various light treatments, plants grown under 100% red LED showed the highest fresh and dry weight of flowers, foliage and roots. The total shoot number, flowering shoot number, and flower number were significantly (P < 0.05) affected by red light spectrum, while the blue light LED and especially monochromatic blue light resulted in growth retardation. The blue light spectrum promoted the proline concentration and oxidative stress markers such as H2O2 and MDA, whereas soluble sugars concentration was higher in plants under red LED light. The highest percentage of hypericin (4.42%/m2), pseudohypericin (8.07%/m2), and hyperforin (50.67%/m2) were detected in flowers under red light treatment, calculated based on square meter. Total phytochrome was higher in the leaves of plants under R50: B50 LED and 100 R:0B treatments. Expression of the photoreceptor and flowering-related genes HpPHYA, CRY1, CRY2, GI, CO and FTL, were affected in plants under sole red light. Molecular studies have shown that red light has a flowering-enhancing effect, in contrast, blue light has a deterrent effect on H. perforatum flowering. This corroborates that red light can promote H. perforatum growth and flowering by inducing morphological, physiological and molecular responses.

Automated summary

The content of secondary metabolites in medicinal plants is influenced by light quality, with red LED promoting growth and blue LED causing growth retardation. Different light spectra have significant regulatory effects on plant growth and yield.