Potential Physiological And Biochemical Mechanisms And Repair Of Cadmium Pollution Of The Environment, Narrow Leaf Cattail Tolerance To Cadmium

ABSTRACTPhytoremediation of cadmium polluted environment has become the frontier and hot research area of environmental and biological science. However, this green technology is limited at present by a fundamental lack of knowledge of the mechanisms and controlling factors involved. The use of higher plant in phytoremediation of cadmium from polluted environment is not only based on their ability to take up, translate and accumulate the cadmium, but also on the mechanisms able to alleviate its toxic effect. Knowledge of these processes is crucial in the understanding of the tolerance to improve plants of biotechnological interest.In this research, Cattail plant (Typha angustifolia Linn) was used as experimental material and the physiological, biochemical mechanisms of cadmium tolerance in Typha angustifolia Linn was studied by hydroponic culture, sewage irrigation, morphological investigation, enzyme hydrolysis, AAS (atomic absorption spectrometry), differential centrifugation technology, ultracentrifugation technology, energy-dispersive X-ray microanalysis technology, solvent extraction, enzyme activity analytical method and some other technology. The results obstained are summarized as follows:Cadmium inhibits the growth and development of Typha angustifolia Linn. Our result showed that in Cd-treated plants (hydroponic culture or sewage irrigation), the change of physiological and biochemical index was more significant than in the controls and was correlated with cadmium treatment concentration. Under hydroponic condition, 5mg I/1 cadmium concentration was the threshold concentration, at which growth of Typha angustifolia Linn was essentially unaffected relative to the control cultures without Cd. This finding is important because it shows that to some extent, Typha angustifolia Linn can do tolerate cadmium.Typha angustifolia Linn has the ability to accumulate cadmium. The results alsoshowed that the transport and partitioning of cadmium in Typha angustifolia Linn is in both apoplasmic and symplasmic pathways, mainly via apoplasmic. In addition,during the investigation of cadmium different levels distribution in Typha angustifolia Linn,we find that:l) as far as the accumulate ability of different organ in Typha angustifolia Linn are concerned,root sheath leaf. 2) in root tissue level of Typha angustifolia Linn,the cadmium content of cortex tissue around the endodermis is highest,the cadmium content of stele tissue and cortex tissue far from endodermis is lower while epidermis cadmium content is lowest. 3) among the cadmium content of cell wall, cytoplasm (excluding the vacuole) and vacuole,cellvacuole>cytoplasm (excluding vacuole);as far as different cell organs are concerned,chloroplast>ribosome>mitochondria>nucleus.In addition, The study of cadmium chemical forms using solvent extration method showed that NaCl extractable cadmium is dominant in both root and leaf of cattail plant.But in root of cattail plant, the content of distilled water and ethanol extractable cadmium is higher than that of NaCl extractable cadmium. These results indicated that cadmium is mainly combined with protein and the transport ability of cadmium in root is more than that of leaf in cattail plant. In addition, the differences of accumulation, transport, partitioning and chemical forms of cadmium in cattail plant between root and leaf suggested that the tolerance mechanism of root is different form that of leaf.Typha angustifolia Linn exposed to different concentration cadmium (CK 0.5 K 5 1CK 50 mg L"1) was investigated in order to know the possible effect of this metal on the glutathione metabolism and glutathione-related enzyme in leaf. Results obtained in this work suggest that the ratio of GSH/GSSG and GST may play a key role in the detoxification process of cadmium in Typha angustifolia Linn.In addition, Typha angustifolia Linn can accumulate cadmium in its shoots with cadmium content up to 800 jig plant"1 DW in a sewage irrigation containing cadmium as high as 5mg L"1. The result showed that Typha angustifolia Linn is...