Picloram enhanced the callus induction, growth kinetics, antioxidant potentials, and secondary metabolites production of Zingiber officinale var. rubrum callus cultures

Abstract

Plant cells are driven by types and concentrations of plant growth regulators to produce callus mass containing bioactive compounds. This study aimed to induce callus and to observe the histological, phytochemicals, and antioxidant basis of the callus. An efficient callus induction protocol was developed using picloram for Malaysian red ginger, Zingiber officinale var. rubrum. The effect of auxinic picloram herbicide was studied using six different concentrations (0, 0.5, 1, 2, 4, and 8 mg/L) on various explants (leaf sheath, leaf, root) to optimise the callus induction. The induced callus was studied for growth kinetics, anatomical features, antioxidant capacity, and phytochemical content. The highest callogenesis frequency (93.75%) and biomass accumulation (3.68 g) were observed on leaf sheath explant cultured on ½ strength Murashige and Skoog (MS) medium supplemented with 8 mg/L which also requires earlier subculture duration (45 days post-inoculation) in comparison to lower concentrations. Morphological investigation through histological procedure demonstrated friable and non-embryogenic characteristics of the primary and subcultured callus. Cultivated leaf sheath (CLS) methanolic extract showed the highest total phenolic (191.26 mg GAE/g dry extract) and flavonoid (4.54 mg QE/g dry extract) contents contributing to antioxidant activity with an estimated EC50 of 0.208 mg/mL. Although comparatively lower than CLS extract, callus extracts showed higher antioxidant activity and significantly lower EC50 values than in vitro leaf sheath extract. 4H-Pyran-4-one, 2,3-dihydro-3,5-dihydroxy-6-methyl-, phenol, and phenolic glucoside were only present in callus cultures while methyl esters, fatty acids, and phytosterols could be obtained from leaf sheath and callus extracts. In conclusion, the callus culture of Z. officinale var. rubrum is a potential renewable source of bioactive phytochemical compounds and can be employed for biotechnological practices such as elicitor-induced accumulation of secondary metabolites and genetic modification.