Effects of copper on total phenolics, flavonoids and mitochondrial properties of Orthosiphon stamineus callus culture

Abstract

Plants need an appropriate amount of copper to sustain their normal growth. However, excess of copper may interrupt plant development and cause stress. In this study, the responses of Orthosiphon stamineus callus culture under various copper concentrations were investigated. Callus cells at 24-days old were treated with 100, 150, 200 and 250 μM of copper solution and harvested after one week. Mitochondria from the calluses were isolated and the total mitochondrial proteins were determined. We used sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) to compare the mitochondrial protein profiles in normal medium and copper-containing medium. The activities of cytochrome c oxidase, as well as the total phenolic and flavonoid contents were determined. The results of atomic absorption spectroscopy (AAS) analysis have shown significant amount of copper accumulated in O. stamineus callus cells, depending on the amount of copper supplied. With the BCF values of more than 10, this species can be categorized as copper hyperaccumulator. When the amount of copper supplied increased, the cells exhibit higher cytochrome c oxidase activities and produce more phenolic compounds, in spite of decreasing amount of total mitochondrial proteins and a lesser number of visible bands visualized from SDS-PAGE analysis. Overall, our findings highlight the dynamic responses of O. stamineus cells when exposed to various levels of copper, notably by alteration of biochemical and mitochondrial properties as their protection mechanism under stress.