The aim of this project is to study the heavy metal tolerance mechanism in Typha latifolia which was collected separately from a contaminated Pb/Zn mine site and a clean fresh water pond in Shaoguan County, Guangdong Province, China. Results of water and soil analyses indicated that the contaminated site was much more polluted with heavy metals. The uptake and accumulation of heavy metals was very high for Typha derived from the contaminated site and especially in the root portion (up to 500 μg/g of Zn and 1000 μg/g of Pb)....[ Read more ]

The aim of this project is to study the heavy metal tolerance mechanism in Typha latifolia which was collected separately from a contaminated Pb/Zn mine site and a clean fresh water pond in Shaoguan County, Guangdong Province, China. Results of water and soil analyses indicated that the contaminated site was much more polluted with heavy metals. The uptake and accumulation of heavy metals was very high for Typha derived from the contaminated site and especially in the root portion (up to 500 μg/g of Zn and 1000 μg/g of Pb).

Results from SEM-EDX analysis revealed that some heavy metals containing amorphous granules were identified in the outer cortical cells of the mature Typha root from the contaminated site. This formation may serve to minimize the transport of heavy metals to the upper sensitive parts of the plants. In TEM-EDX studies, results showed that the heavy metals (Zn, Pb & Fe) were localized in the apoplast of cortical cells of Typha adventitious root and particularly in the intercellular spaces. In addition, the formation of the mineral deposits inside the cortical cells as revealed by X-ray elemental mapping may also play a role in metal detoxification in Typha plants grown in mine site. In the LM study, however, it was observed that the endodermis of Typha adventitious root derived from mine site had a thicker suberized cell wall than the one derived from the clean site, suggesting that the thickened wall may act as a barrier to the radial transport of heavy metals into the stele.

Moreover, results of Typha root tissue fractionation showed a large proportion (>98%) of the heavy metals (Zn, Fe and Pb) was accumulated in the cell wall fraction, further supporting the idea that the Typha root cell wall has a high intrinsic metal ions binding capacity and can act as an important storage site for heavy metals. Meanwhile, studies by gel filtration, paper chromatography and infrared spectroscopy indicated the presence of a glucose-Zn binding complex isolated from the cytoplasmic fraction of Typha root tissue. However, their role in relation to metal tolerance in Typha plants has not yet confirmed.