Effect of Melatonin on the Biomass and Secondary Metabolite Production in Adventitious Root Culture of Macrotyloma uniflorum

Abstract

The underutilized pulse crop Macrotyloma uniflorum, also known as "Horse gram," has a high nutritional value and a variety of pharmacological effects. There have been no in vitro studies on the enhancement of the production of biomass and phytochemicals from adventitious root derived callus culture of M. uniflorum. Using adventitious roots as an explant cultured on MS media enriched with melatonin at varied concentrations, we have developed a workable strategy for production of biomass and pharmacologically important secondary metabolites in the study described here. Among all the various concentrations of melatonin the maximum biomass was obtained at the concentration of 0.6 mg/L of melatonin. The maximum biomass recorded was (FW = 370.25 ± 7.4 g/L, DW = 29.62 ± 0.88). While the maximum production of the phytochemicals were seen at a concentration of 1.0 mg/L of melatonin which means that there was a negative correlation between the production of the biomass and the enhancement of production of phytochemicals hence the study becomes a growth non associated study. The HPLC analysis confirmed the maximum accumulation of phytochemicals such as Gallic acid (9.24 ± 1.01 mg/g DW), Catechin (1.36 ± 0.01 mg/g DW), Caffeic acid (2.74 ± 0.07 mg/g DW), Epicatechin (2.45 ± 0.09 mg/g DW), Rutin (1.75 ± 0.05 mg/g DW), Myricetin (6.77 ± 1.03 mg/g DW), Daidzein (5.31 ± 1.07 mg/g DW), Genistein (4.11 ± 0.06 mg/g DW), Kaempferol (4.88 ± 0.11 mg/g DW). The antioxidant activities (in-vitro and in-vivo) showed highest levels at 1.0 mg/L of melatonin like in the case of production of phytochemicals. So, we can say that there is a positive correlation of the phytochemicals with the antioxidant potential. Therefore it can be said that these phytochemicals are contributing directly to the antioxidant activities of the callus. The maximum levels of antioxidant activities are ORAC = 567.52 ± 4.1 (µM TEAC), CUPRAC = 357.85 ± 0.62 (µM TEAC), FRAP = 431.12 ± 1.33 (µM TEAC) and CAA = 58.88%. These results show that biotic elicitor that is melatonin in this case has the potential to increase the biomass production of adventitious root culture of Macrotyloma uniflorum. And it is also useful in increasing the production of phytochemicals which are contributing to the antioxidant potential of the callus. Therefore, in light of the fact that melatonin effectively influences the development of medicinally significant phytochemicals, it can be inferred that M. uniflorum can play a key role in therapeutics due to the rise in the production of phytochemicals that directly impact antioxidant activities