Subcellular distribution of chromium in accumulating plant Leersia hexandra Swartz
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The subcellular distribution of chromium in Leersia hexandra Swartz, a Cr-accumulating plant found in China, was studied by differential centrifugation, transmission electron microscope and energy dispersive analysis of X-ray. Subcellular fractionation of Cr-containing tissues showed that most of the accumulated Cr was isolated to the cell walls in roots and the vacuoles in leaves. When the plant was grown in a nutrient solution containing 60 mg L−1 Cr, 83.2% of the root Cr was localized in the cell wall fraction, while 57.5% of leaf Cr was localized in the vacuole and cytoplasm fraction. Transmission electron microscopic analysis revealed that those cell compartments contained especially electron dense areas. Energy dispersive X-ray spectra showed the electron dense areas contained high Cr. However, the dark electron precipitates were never observed in the plant cells without Cr treatment. In all treatment groups (5, 30 and 60 mg L−1), the fraction containing the lowest level of Cr was the organelle fraction in roots as well as leaves. These results indicated that Cr accumulated in the L. hexandra was preferentially stored in the cell walls of roots and the vacuoles of leaves. This phenomenon diverted Cr ions from metabolically active compartment (chloroplast, mitochondria), resulting in a reduction of Cr toxicity in the plant cell.
KeywordsChromium Leersia hexandra Swartz Subcellular distribution Compartmentalization Tolerance
transmission electron microscope
flame atomic absorption spectrophotometer
energy dispersive analysis of X-ray
cell wall fraction
cytoplasm and vacuole fraction
Fisher’s least significant difference
The authors thank the financial supports from the Scientific Research and Technological Development Project of Guangxi (GuiKeGong 0816003-1-1), the Natural Science Foundation of China (30760049, 40663002, 20665003) and the Provincial Natural Science Foundation of Guangxi (GuiKeNeng 0701K005, GuiKeZi 0728222). Financial assistance for this research was also provided through the Program to Sponsor Teams for Innovation in the Construction of Talent Highlands in Guangxi (GuiKeRen 2007-71, 2004217). Two anonymous reviewers are thanked for their cogent reviews of the manuscript.
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