Polycyclic aromatic hydrocarbons (PAHs) are a group of persistent organic contaminants commonly found in the environment. Due to their highly mutagenic and carcinogenic properties, their behaviors and fate in the soil/water plant system are of great environmental concern. Because plants form the basis of human and animal food webs, potentially harmful organic contaminants including PAHs could find their way into human and animal populations via this route. Clearly, increased understanding of how plants take up and accumulate PAHs from the environment could have considerable benefit for risk assessments.
In recent decades, considerable interest in the uptake of PAHs by plants has emerged. Plants can be exposed to PAHs in different ways. Foliage uptake of atmospheric PAHs occurs via the deposition of particle-bound compounds and the retention of vapor-phase PAHs on waxy leaf cuticles. The rate and extent of plant root uptake depends on the physiochemical properties of the PAHs, soil characteristics, and plant species and physiology. Recently, metabolisms of PAHs have been observed and proven to be related to the enzyme activities in plant bodies. To this end, how to control and regulate the activity of plant enzymes and PAH metabolism is of worldwide concerns. However, little information is available on this subject.
In this work, impacts of inhibitor and safener on the activities of PPO (phenol oxidase) and POD (peroxidase) and the metabolism of phenanthrene as a representative of polycyclic aromatic hydrocarbons (PAHs) in roots of tall fescue (Festuca arundinacea) were investigated utilizing hydroponic cultivation system in a greenhouse. 0.3% NaCl and 2.00 mg/L Vc were chosen as representatives of safener and inhibitor. Root concentrations of phenanthrene were found to be significantly higher with the addition of 2.00 mg/L 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.
To our knowledge, this is a primary investigation on the inhibitor and safener regulated uptake of PAHs by plant. Results of this work would be of high values in risk assessments of organic contaminants in the environment.