No abstract

The effect of initial sucrose concentration was investigated in root suspension cultures of Morinda citrifolia to improve root growth and secondary metabolites production, i.e. anthraquinone, phenolics and flavonoids. Besides, oxidative stress level, antioxidant enzymes activity and membranes damage under different sucrose concentration were estimated. A 5% sucrose supply was shown to be optimal for the production of root dry mass, but higher sucrose concentrations of 7-9% inhibited the accumulation of root dry weight (DW). However, the maximum production of anthraquinone (251.89 g L -1 DW), phenolics (165.14 g L -1 DW) and flavonoids (163.56 g L -1 DW) were achieved at 1% sucrose-treated culture, which may be a source carbon skeletons for secondary metabolism. At the same time was observed low oxidative damage, which could be associated with high levels of secondary metabolites and the increased activity of catalase. Although, catalase (CAT) activity were stimulated at 7-9% sucrose-treated cultures, high accumulation of hydrogen peroxide (H 2 O 2 ) and peroxidation of lipid (MDA) was induced. The observed high activity of CAT and guaiacol peroxidase (G-POD) were not sufficient enough to mitigate the toxic effect of H 2 O 2 .

Morinda citrifolia adventitious roots were cultured in shake flasks using Murashige and Skoog medium with different types and concentrations of auxin and cytokinin. Root (fresh weight and dry weight) accumulation was enhanced at 5 mg l -1 indole butyric acid (IBA) and at 7 and 9 mg l -1 naphthalene acetic acid (NAA). On the other hand, 9 mg l -1 NAA decreased the anthraquinone, phenolic and flavonoid contents more severely than 9 mg l -1 IBA. When adventitious roots were treated with kinetin (0.1, 0.3 and 0.5 mg l -1 ) and thidiazuron (TDZ; 0.1, 0.3 and 0.5 mg l -1 ) in combination with 5 mg l -1 IBA, fresh weight and dry weight decreased but secondary metabolite content increased. The secondary metabolite content (including 1,1-diphenyl-2-picrylhydrazyl activity) increased more in TDZ-treated than in kinetin-treated roots. Antioxidative enzymes such as catalase (CAT) and guaiacol peroxidase (G-POD), which play important roles in plant defense, also increased. A strong decrease in ascorbate peroxidase activity resulted in a high accumulation of hydrogen peroxide. This indicates that adventitious roots can grow under stress conditions with induced CAT and G-POD activities and higher accumulations of secondary metabolites. These results suggest that 5 mg l -1 IBA supplementation is useful for growth and secondary metabolite production in adventitious roots of M. citrifolia.