Lead Accumulation and Isolation of Associated Rhizobacteria in Rice Grown in Lead Contaminated Soil

摘要

Lead accumulation in rice was studied using transmission electron microscope (TEM). The type of rhizobacteria associated with rice grown in lead contaminated soil was also examined. The results showed that rice plants accumulated lead in roots (5,735 mg/kg), stems and leaves (0.0820 mg/kg) and grains (0.0169 mg/kg). The concentration of lead in rice grains did not exceed the European Union Standard for lead in cereals (0.2 mg/kg) indicating that the seeds grown in lead contaminated soil were at acceptable levels. TEM studies were performed on root, stems and leaves of rice grown in control and lead contaminated soil after 120 days of planting. Most lead was accumulated in root cells in vacuoles of xylem parenchyma cell, lumen of xylem vessels, intercellular space of parenchyma in cortex and little was found in the cytoplasm. In stem cells, lead was found mostly in vacuoles of xylem vessels with very small amounts noted in the cell wall, intercellular space and cytoplasm. Leaf cell lead deposits appeared in vacuoles of xylem parenchyma cells with very small amounts noted in intercellular space and cell wall. Bacterial sampling of the rhizosphere identified four species of bacteria in lead contaminated soil associated with the roots of rice plants, namely Pseudomonas chlororaphis subsp. aureofaciens, Microvirgula sp., Enterobacter sp. and Bacillus sp. These results provide a baseline description of soil bacteria associated with the roots of rice plants growing in lead contaminated soil.