Impact of Metals on Secondary Metabolites Production and Plant Morphology in Vetiver Grass (<i>Chrysopogon zizanioides</i>)

Abstract

The impact of selected metals on the production of phenolic compounds was investigated in a pot trial experiment. One-month old vetiver grass (Chrysopogon zizanioides) seedlings were exposed to different concentrations (0, 10, 50, 100, and 500 ppm) of As, Cr, Cu, Fe, Ni, Pb and Zn. All the plants except for those treated with As tolerated up to 500 ppm as they did not show any signs of stress such as wilting or necrosis. A significant decrease (>35 %) in the length of the plants treated with As, compared to the control, was observed at 50 ppm which further decreased with increasing As concentration. A serious case of phytotoxicity was observed at 500 ppm As as the plant could not survive. Total soluble phenolics content in vetiver plants increased with increasing concentration of metals in the growth medium. The amount of the cell wall-bound phenolics (2.01 to 5.84 mg GAE g^–1 DW) was higher than the total soluble phenolics (1.13 to 2.14 mg GAE g^–1 dry weight DW) and both increased with increasing metal concentrations. Morphological changes associated with metal-induced stress were also examined with a scanning electron microscope which revealed thickened cell walls, loss of cell shape, reduction of intercellular space and the closure of stomata in leaves of metal-exposed plants.

Keywords: Vetiver grass, toxic metals, phytotoxicity, phenolic compounds, morphological changes