Abstract
The aim of this work was to determine the effect of stress conditions caused by different light sources, i.e., blue LED (λ = 430 nm), red LED (λ = 670 nm), blue and red LED (70%:30%) and white LED (430–670 nm) on the growth and morphology of cultivated in vitro Dracocephalum forrestii shoot culture. It also examines the effects on bioactive phenolic compound production and photosynthetic pigment content, as well as on antioxidant enzyme activity (CAT, SOD, POD) and antioxidant properties. The most beneficial proliferation effect was observed under white LEDs (7.1 ± 2.1 shoots per explant). The white and blue lights stimulated the highest fresh weight gain, while red light induced the highest dry weight gain. The total phenolic acid content ranged from 13.824 ± 1.181 to 20.018 ± 801 mg g DW−1 depending on light conditions. The highest content of rosmarinic acid was found in the control shoots (cultivated under fluorescent lamps), followed by culture grown under red light. All LED treatments, especially red and blue, increased salvianolic acid B content, and blue increased apigenin p-coumarylrhamnoside biosynthesis. The greatest ferric reduction activity was observed in shoots cultivated under red light, followed by blue; this is associated with the presence of the highest total phenol content, especially phenolic acids. Similarly, the highest DPPH radical scavenging potential was observed under red light followed by blue. This study proves that LEDs have emerged as significant support for directed in vitro propagation, taking advantage of specific stress responses on various light spectra. This study also showed how stress induced by different LED light spectra increases in Dracocephalum forrestii the synthesis of pharmacologically-active compounds. Hence, light stress may turn out to be a simpler alternative to metabolic engineering for improving the production of secondary metabolites of therapeutic value.
Highlights
Plant secondary metabolites are usually studied in the context of their role in plant defence against abiotic and biotic stresses
Little data is available regarding the correlation between the culture light conditions and the mechanisms underlying the physiological secondary metabolism in D. forrestii
Our findings indicate that under controlled in vitro conditions, manipulation of light quality could induce significant changes to physiological and biochemical responses of D. forrestii shoot culture
Summary
The production and accumulation of secondary metabolites (SM) is an example of a sophisticated process developed by plants to facilitate survival and adaptation This heterogeneous group of compounds is involved in defence against abiotic and biotic stresses, as well as in signalling of symbiotic communication, attracting pollinating animals and protecting plants from UV radiation and oxidants [1]. Phenolic compounds are chemically a very diverse group that encompass several thousand SM in higher plants but are uncommon in bacteria, fungi and algae They are considered to play a crucial role in the antioxidative defence system by neutralising free radicals and other oxidative agents released under environmental stress conditions, typically high light level, nutrient deficiency, low temperatures and pathogen infection. A body of evidence suggests that plant phenolics support the capability of plants to scavenge reactive oxygen species (ROS) [2,3]
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