Spectral lights based treatment enhanced biomass accumulation and secondary metabolites production in callus culture of Citrus reticulata

Citrus reticulata is a common fruit, belongs to the family Rutaceae. It contains terpenes, phenolics, flavonoids, and vitamin C in conjugation with sugars, amino acids, minerals, organic acids and other biologically important compounds. Application of light elicitation strategies in in vitro plant cultures is acquiring more interest for their potential in feasible biomass accumulation and therapeutically important secondary metabolites production. The present study was designed to investigate the effects of different monochromatic lights (white, red, blue, green, and yellow) on the proliferation and secondary metabolites accumulation in callus cultures of Citrus reticulata raised in response to treatment with AgNPs and TDZ. Silver NPs were synthesized by using green method, followed by characterization of these NPs. Nucellus tissues obtained from seeds of C. reticulata and inoculated on MS medium supplemented with TDZ (1 mg/L) + AgNPs (20 ppm) for callus development. To examine the effects of different light spectrum, the developing calli was sub-cultured on similar media and incubated in growth chamber under five different light treatments (white, red, blue, green, and yellow). Total protein content, chlorophyll content, phenolic and flavonoid content, along with activity of antioxidant enzymes on all samples was also analyzed. Highest callus fresh weight (730.21 mg) was recorded in callus cultures proliferated under white light condition. Phytochemical analysis of callus cultures showed significantly higher values for TPC, TFC and antioxidant activity under red light. However, maximum production of anti-oxidative enzymes (SOD and POD) was recorded under blue light. White light is considered more favorable for accumulation of total protein content. To our knowledge, this is the first study on production of biomass and phytochemicals in response to different monochromatic lights in callus cultures of Citrus reticulata. The present research outcomes clearly exhibited the interest to apply monochromatic light as elicitor of in vitro callus cultures to promote the production of biomass and important bioactive metabolites.