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Effects of Enzymes on Metabolism of Polycyclic Aromatic Hydrocarbons in Plant

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Tutor: GaoYanZheng
School: Nanjing Agricultural College
Course: Environmental Science
Keywords: Polycyclic aromatic hydrocarbons (PAHs),Plant metabolism,Peroxidase (POD),Phenol
CLC: X173
Type: Master's thesis
Year:  2011
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Abstract:
Nowadays, organic pollution is a serious environmental problem in the world. Polycyclic aromatic hydrocarbons (PAHs) are a group of persistent organic contaminants commonly found in the environment. How to remediate the contaminated soils by organic contaminants including PAHs (Polycyclic Aromatic Hydrocarbons) is of worldwide concerns. Plant metabolism of PAHs plays an important role of Phytoremediation. However, researches on plant metabolism of PAHs are still rarely reported. Enzyme plays an important role in bioremediation and plant metabolism. Understanding the effects of enzymes on metabolism of PAHs would be very helpful and instructive to exploring the mechanism of plant metabolism, and is paramount of determinations of remediation strategies for soil contamination.Effects of enzymes on metabolism of phenanthrene, naphthalene and anthracene as representatives in plants were investigated. Tall Fescue was selected as tested plants. In this work, effects of peroxidase (POD) and phenol oxidase (PPO) in shoot and root of plant on metabolism of phenanthrene were studied. The effects of inhibitor and safener on enzyme activity and phenanthrene metabolism in root of tall fescue were elucidated. Using in vitro enzymatic and fluorescence, the effects of phenol oxidase and horseradish peroxidase on phenanthrene, naphthalene and anthracene metabolic process were investigated. Main results of this work are shown as follows:(1) The effects of peroxidase (POD) and phenol oxidase (PPO) in shoot and root of Tall Fescue on metabolism of phenanthrene were studied. The concentrations of phenanthrene in treatment groups in 12,24,48 h were all higher than the control groups, and the concentrations of phenanthrene in root were much higher than in shoot. The metabolic process was blocked because of the enzymes inactivated in treatment groups. The activities of POD decreased thereafter with increasing the concentrations of phenanthrene from 1 to 4 mg·L-1 in same treatment time. The lower the activities of POD in shoot and root of plant, the lower the metabolic efficiency of phenanthrene was. The activities of PPO in shoots were increased with increasing treatment time, while the activities of PPO in roots were first decreased and increased. The higher the activities of PPO in root, the higher the metabolic amount was.(2) Impacts of inhibitor and safener on the activities of PPO and POD and the metabolism of phenanthrene as a representative of PAHs in roots of tall fescue were investigated utilizing hydroponic cultivation system in a greenhouse. Root concentrations of phenanthrene were found to be significantly higher with the addition of 2.00 mg/L ascorbic acid(Vc) in 1-16 d. However, no significant difference was seen for root concentrations of phenanthrene with the addition test safener. The activities of PPO and POD in root were much lower with the addition of Vc, and were only 1/6 and 1/9 of the controls without inhibitor or safener, respectively, indicating the strong inhibition of test inhibitor on PPO and POD activity. In contrast, no significant difference was observed between the test enzyme activity with and without the addition of safener (0.3% NaCl). The initial activity of enzyme in roots of tall fescue is a key factor of the phenanthrene metabolism. With the addition of test inhibitor, the inhibition efficiency of enzyme activity was positively correlated to the inhibition efficiency of phenanthrene metabolism. This indicates that the inhibitor affected the metabolism of phenanthrene in root mainly by regulating the enzyme activity.(3) The effects of HRP and PPO on metabolism of phenanthrene, naphthalene and anthracene were investigated utilizing in vitro enzymatic and fluorescence. The metabolic rate of phenanthrene was increased rapidly in 0-26min by the action of HRP, while in 26-60min the metabolic rate of phenanthrene was essentially unchanged, and anthracene was also the same order as phenanthrene. The metabolic rate of naphthalene by the action of HRP and PPO was higher than control, and was 3.52% and 16.51%, respectively. Additionally, the metabolic rate of the tested three PAHs by the effects of HRP increased following the order of anthracene>phenanthrene> naphthalene. By contrast, the metabolic rate of the tested three PAHs by the effects of PPO was basically the same.
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