| Phytoremediation enhancement by mirobes is the hot point of current research. Endophytic bacteria, colonized in plant tissues, could enhance the efficiency of phytoremediation, such as increasing plant biomass, stengthing heavy metal resistance and promoting metals absorption. However, the mechanisms were still not clear. In this research, we tried to clear the mehanisms of plant growth promotion and heavy metal phytoextraction enhancement by endophytic bactiera with pot experiment, nutrient solution experiment and tissue culture experiment. The main results as following:1) With PCR-DGGE method, the endophytic bacterial community structure was determined by two different DNA extraction methods:culture extraction and direct extraction. The result showed that the detected 26 endophytic bacteria mainly belongs to Proteobacteria, Firmicutes and Actinobacteria. Three Proteobacteria endophytic bacteria Sphingomonas, Pseudomonas fluorescens, Acinetobacter calcoaceticus used in this study showed great ability of plant growth promotion, heavy metals resistance and translocation enhancement, which greatly contributed to the enhancement of phytoremediation by endophytic bacteria.2) With pot experiment, we found that the Sasm05 inoculation could significantly increase plant biomass and ability of phytoextraction. The total biomass of Sedum alfredii was increased by 33%, the total extraction of Cd, Zn and Pb were increased by 61%、42% and 56%, which removed 18%,3% and 1% of total metals in soil. To salination-Cd combined comtaminated soil, plant growth promoting endophytic bacteria Sasm03 could not only enhance absorption and accumulation of Cd by Sedum alfredii, but also increase rape biomass by 10-20%, and decrease Cd and nitrate concentration by 16% and 25%. Meanwhile, the endophytic bacterium Sasm03 inoculation significantly promoted plant growth, enhanced diversity of bacterial community, increased the numbers of denitrifying bacteria, and strengthened denitrification, which may the main reasons to decrease nitrate concentration in rape.3) By a hydroponic experiment, the aim of this study was to clarify the effects of inoculating an endophytic bacterium Sphingomonas SaMR12 on phytoremediation with special emphasis on changes of Zn/Cd uptake, plant growth, root morphology, and organic acids secretion at different Zn/Cd treated levels. Under Zn treatment, SaMR12 inoculation increased plant biomass by 45%, the total root length and number of root tips were increased by 26% and 33%, the secretion of malic acid and oxalic acid were increase by 2～4 folds, and IAA concentration was increased by 26%. Under Cd treatment, SaMR12 inoculation increased plant biomass by 27%, the total root length and number of root tips were increased by 26～54% and 18～56%, the secretion of critic acid, malic acid and oxalic were increased by 25～141%, and the O2 and H2O2 concentration in plant were decreased by 13% and 21%. In conclusion, the SaMR12 increased plant biomass in Zn treament by producing IAA, and enhanced Cd resistance in Cd treatment. Finally, the phytoextraction of Zn/Cd was enhanced.4) To determine the effects of endophytic bacteria Sasm05 on root elongation and shoot growth, the tissue culture was used to determine the changes of root morphology and chlorophyll content under Sasm05 inoculation. The IAA transport inhibitor NPA treatment showed that the IAA could not enhance root elongation and Cd phytoextration. However, the Sasm05 treatment could significantly increase plant biomass by 45%, Cd phytoextraction by 19%. Moreover, the inoculation could also increase the content of chlorophyll by 24～44%, the activity of Mg2+-ATPase and Ca2+-ATPase were enhanced by 47% and 44%, respectively. So, we believe the plant growth promotion and phytoextraction enhancement were not only resulted from IAA producing by endophytic bacteria, but also resulted from the chlorophyll synthesis promotion and the activity enhancement of Mg2+-ATPase and Ca2+-ATPase which related with membrane transport of metal ions. |
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