Study On Physiological Responses Of Two Kinds Of Colored-leaf Privet To SO₂ Sress

Sulfur dioxide is one of the most common and harmful gas, the usage of plants with high absorbency to certain air pollutant in atmospheric pollution control has become a focus. In order to investigate the effect of different concentrations of sulfur dioxide treatment on physiological characteristics of colored-leaf plants and to screen the identification physiological indicators of SO2-tolerance ability, two annual golden-leaf shrubs (Ligustrum X vicaryi and Ligustrum japonicum’Howardii’) have been studied and an artificial static fumigation system has been used. The study also explored the mechanism of chlorophyll biosynthesis in two golden-leaf plants to investigate possible acting sites of SO2 stress on chlorophyll biosynthesis. The main results were as follows:1. The contents of osmoregulation substance such as free proline and amino acids in two colored-leaf plants had small changes over time prolonged with low concentration of SO2(20 mg/m3). The three osmoregulation substances of L. ×vicaryi increased significantly and gradually increased with the treatment of 40 mg/m3 SO2 fumigation and 80 mg/m3 SO2 fumigation, respectively. Three kinds of substances with the smoked SO2 gas concentration increased gradually, but did not change significantly with the treatment of 20 mg/m3 over fumigation time.2.80 mg/m3 fumigation induced the activities of three major antioxidant enzymes in two kinds of colored-leaf plants significantly after one-day fumigation. The activities of superoxide dismutase, peroxidase were maximum after three-days fumigation, but the activity of catalase were maximum after five. L. ×vicaryi mainly relied on POD and CAT to removal of H202which was catalyzed by SOD after three-days and five-days fumigation, respectively. CAT played a major role in subsequent times. The three enzymes which were scorbate peroxidase, ascorbate oxidase and glutathione reductase in leaves of two species played a major role after five-days fumigation.3. The membrane permeability and malondialdehyde content of two colored-leaf species were significantly increased with increasing concentration of SO2 which showed a significant feature of oxidative stress. The membrane permeability and malondialdehyde content of L. ×vicaryi were the highest level after seven-days fumigation with the treatment of 80 mg/m. For L. japonicum’Howardii’, the stress injury of five-days fumigation was more serious than those fumigation times. Both membrane permeability and malondialdehyde content of L. japonicum’Howardii’reduced with 80 mg/m3 fumigation. The injury of SO2 stress was reversible and L. japonicum’Howardii’still be able to recover resistance to SO2.Plants restore their resistance to SO2 require a process.4. The results of principal component analysis showed that the original twelve indicators were converted into three separate new indexes, which cumulative contribution rate was 96.26%. The main indicators which were Pro, SP, FAA, POD, APX and MDA to evaluate the ability of anti-SO2 pollution of two colored-leaf plants were determined by the eigenvectors of each indicators.5. The results of subordinate function analysis suggested that the growth rate of subordinate function values(U value) of L. Xvicaryi was lower than those of L. japonicum ’Howardii’and it showed that the latter was more resistant to SO2 stress than the former.6. The contents of uroporphyrinoge Ⅲ(UrogenⅢ), protoporphyrin Ⅸ(Proto Ⅸ), Mg-protoporphyrin Ⅸ(Mg-Proto Ⅸ), and chlorophyll a and b were increased with the raise of SO2 treatments, then decreased at the 80 mg·m-3. Furthermore, the activities of δ-aminolevulinate dehydratase and uroporporphyrinogn III synthase(UROS) exhibited the similar trend. In contrast, the contents of δ-aminolevulinic acid (ALA) and porphobilinogen (PBG) were significantly lower than those in control under lower treatments, and greatly higher than those in control under 80 mg/m3. Chlorophyll biosynthesis in leaves of two colored-leaf species was presumably blocked at the step from PBG to Urogen III under the SO2 stress. SO2 stress reduced ALAD and UROS activities of chlorophyll synthesis pathway was a key cause of chlorophyll synthesis blocking.