| Lemna minor is a free-floating plant distributed mainly in static aquatic habitats. As a model aquatic plant, L. minor has been widely used to test toxicity of contaminants for its small size, simple structure, rapid growth, easy cultivation and wide distribution. It has a strong accumulation capacity of metals, such as chromium, cadmium and other heavy metals from pollution water. It also can accelerate the transformation of nitrogen and phosphorus from eutrophic waters. In this paper, the ecotoxicological effects of aniline on L, minor have been evaluated based on both morphological and physiological responses. The results were shown as the follows:1. The frond numbers of L. minor in both control and treatment groups tended to increase steadily during the experiment. However, the increase of the frond numbers in the treatment groups was significantly inhibited compared with control at the end of the experiment. There were also significant differences of the frond numbers and the relative growth rate based on frond numbers among the treatment groups at the end of the experiment.2. Aniline could accelerate the etiolation of the fronds. At the end of the experiment, there was a significant difference in the ratios of the yellow frond number/the total frond number among different groups. The effect of aniline on the etiolation of the fronds was significantly correlated with its concentration.3. There was a significant difference to the growth of frond areas and the root length during the experiment, the frond areas and the root length in the treatment groups decreased significantly compared with control, and there was a significant negative linear relationship between the frond areas or the root length and aniline concentration at the end of the experiment.4. Compared with control, the dry weight and fresh weight of L. minor in each experiment group significantly decreased. Additionally, there was a significant negative correlation between the biomass and the aniline concentration. In all experiment groups, growth index was significantly smaller than that in control. The inhibitory effect of aniline on growth index of I. minor was negatively correlated with its concentration.5. After exposed to aniline for24hours, the contents of both chlorophyll a and b had no difference in G1and G2, but went down significantly in group G3, G4, G5, and G6compared with control. It suggested that aniline had an acute toxic effect on chlorophyll a and b contents in L. minor when its concentration was equal to or above0.4g1-1.6. Compared with the control, the MDA content of L. minor in each experiment group significantly decreased after treatment of3and7days. Additionally, there was a significantly positive correlation between the MDA content and the aniline concentration.7. The results of activities of CAT, POD, and SOD in L. minor varied after exposed to aniline24h,72h, and120h. After exposed to aniline with or over1g1-1, CAT activity significantly reduced compared with control. POD activity increased only after72h treated by aniline with the concentration between0.1-0.4g1-1, but decreased when the concentration was over0.4g1-1. At the lower concentration of aniline (0.4-0.8g1-1), SOD activity significantly increased, but decreased at the higher concentration of aniline (>0.4g1-1). The activities of three anti-oxidative enzymes had different responses to aniline at different times.8. Aniline did not increase the pH values of water-body. This result suggested that aniline did not affect the growth and metabolism of L. minor by the changes of pH values of its environments.Based on the results above, we can conclude that L. minor could be used as an indicator for aniline pollution in aquatic environments for that many morphological parameters of L. minor are sensitive to aniline. |
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