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

Identifying a suscessul plant propagation method is very important to preserve wild plants as a genetic source. Hence, plant cells are driven by types and concentrations of plant growth regulators to produce in vitro callus mass to synthesize bioactive compounds. The aim of the present study is to induce callus from red ginger and to evaluate its suitability as a biofactory in terms of histology, phytochemical content and antioxidant potential. This is the first study to provide concrete evidence for the use of picloram for red ginger, Zingiber officinale var. rubrum. In this work, effect of different concentrations of auxinic picloram herbicide (0, 0.5, 1, 2, 4, and 8 mg/L) was evaluated on the callus induction of Zingiber officinale var. rubrum on various explants (leaf sheath, leaf, root). 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 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 which are used for secondary metabolite production. 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 (IVLS extract). 4 H-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. Notably beta-sitosterol was the highest in callus extracts while stigmasterol was only available in IVLS extracts. These phytosterols also responsible for synergistic antioxidant activity exhibited by callus extracts and IVLS, respectively. In conclusion, the callus culture of Z. officinale var. rubrum has been proven by the histological and phytochemical studies as a potential renewable source of bioactive phytochemical compounds. In the future, it can be employed for biotechnological practices such as elicitor-induced accumulation of secondary metabolites and genetic modification. Graphical abstract: [Figure not available: see fulltext.]