Effects of Trace Elements in Culture Medium on Growth, Flavonoids Content and Intracellular Metabolite Allelopathy of Carpesium macrocephalum

  Objective  Effects of trace elements in medium on the growth, flavonoids content and allelopathy activity by the intracellular metabolites of Carpesium macrocephalum in a suspension culture were studied to promote the development of a full scale utilization of C.macrocephalum culture.

  Method  Eight minerals in varied concentrations were incorporated in the culture medium to determine their effects on the growth and flavonoids accumulation in the cells. The allelopathic potential of the metabolite extract from each of the resulting cultures on selected plant seedlings was also determined using a microactivity assay. An NT medium with added 1.0 mg·L^-1 NAA +0.2 mg·L^-1 BA was the basal medium applied for the experiment.

  Result  The cell growth and flavonoids biosynthesis of C. macrocephalum in the suspension culture increased initially followed with a decline as the concentration of Zn²⁺, Co²⁺, MoO₄^2-, Cu²⁺, or BO₃^3- increased in the medium. When the concentration of MoO₄^2- was 3.0 μmol·L^-1 and Zn²⁺ 0.06 mmol·L^-1, the flavonoids content was 1.53% and 1.46%, respectively, representing 1.25 and 1.20 times, respectively, of those of control. The addition of 0.4 μmol·L^-1 Cu²⁺, 0.4 mmol·L^-1 BO₃^3- or 0.2 μmol·L^-1 Co²⁺ yielded 1.35% flavonoids, which was 1.11 times as much as that in control. In between 0.1 and 0.8 mmol·L^-1 of Mn²⁺, the flavonoids content decreased gradually from 1.22% to 0.43%, while 5-20 μmol·L^-1 of I^- did not significantly affect the content. The presence of 0.1 mmol·L^-1 Fe²⁺ appeared most conducive to the cell growth and flavonoids formation. The yield of flavonoids increased in the order of the addition of Zn²⁺, MoO₄^2-, Cu²⁺, BO₃^3-, Co²⁺, I^-, Mn²⁺, and Fe²⁺. The ethanol extracts of metabolites in the cultures exerted varying allelopathic inhibitory effects on the seedlings of Abutilon theophrasti, Bidens pilosa, Cucumis sativus and Glycine max with EC₅₀ of 19.86, 14.69, 19.03 and 59.07 mg·mL^-1, respectively.

  Conclusion  Appropriate addition of trace elements in the medium was conducive to the growth of C.macrocephalum cells and the biosynthesis of flavonoids. However, excessive concentrations of trace elements would decreased flavonoid biosynthesis. Intracellular metabolites of C.macrocephalum suspension cells had different degrees of allelopathic effects on 4 receptor plants.