Root and Shoot Peroxidase Activity in Festuca arundinacea in Light Oil-Contaminated Soil

Abstract

Peroxidases are a group of enzymes that occur especially in plant cells. They are classified as oxido-reductases and are given the official EC number 1.11.1. For many of these enzymes the optimal substrate is hydrogen peroxide, but others are more active with organic hydroperoxides such as lipid peroxides. Peroxidases can contain a heme cofactor in their active sites, or redox-active cysteine or selenocysteine residues. Toxic molecules such as superoxide and hydroxide radicals can be found in cells due to the presence of oxygen. These are byproducts of aerobic respiration. They are eliminated by a number of enzymes present inside the cell such as peroxidases. Some oil-producing countries may encounter the risk of soil pollution by oil, during transportation, extraction and refining of crude oil. Oil-contaminated soil can be hazardous to plants and soil microorganisms. Among the plants, grasses such as Festuca arundinacea (Tall fescue) and legumes have high potential on removal of oil from contaminated soil. In the process of phytoremediation of crude oil, some morphological, enzymatic and physiological changes were observed in plants. In this study, the effect of light crude oil (5 % v/w) in soil on the activity of peroxidase was studied and compared with control. Our results showed that in both roots and shoots, the K_m and V_max of the enzyme were changed. The contaminated soil caused delay of germination and chlorosis in plants. In the contaminated soil, the K_m of root peroxidase was determined to be about 55.5 µM while it was 91 µM in control. The V_max of root’s enzyme was 2 and 6 nmol/mg protein/min in contaminated soil and control, respectively. The K_m of enzyme in shoots was determined to be about 36 and 42 µM in contaminated soil and control, respectively, while the V_max in control was about 1.4 nmol/mg protein/min and it decreased to 1 nmol/mg protein/min in contaminated soil. The specific activity of enzyme in root control was 5.3 × 10⁻³ U/mg protein while it was 3.5 × 10⁻³ U/mg protein in contaminated roots. The specific activity of enzyme in shoots was 1.8 × 10⁻³ and 1.7 × 10⁻³ U/mg protein in control and contaminated soil respectively. Our results propose that in the root grown in contaminated soil, the plant uses peroxidase isoform in comparison with control roots, while in the shoots the same peroxidase was used in the plant in both contaminated and control.