Influence of selenium on lead absorption and localization in meristematic cells of Allium sativum L. and Pisum sativum L. roots

The effect of different concentrations (80-640 muM) of sodium selenate and sodium selenite on lead absorption by Allium sativum (selenium absorber) and Pisum sativum (selenium nonaccumulator) roots treated with 10 muM Pb(NO3)(2) was investigated. Lead alone and with either of the selenium compounds was supplied in aqueous solutions for 24 h. Selenite diminished lead content in the two plant species' roots more effectively than selenate. The rhodizonate method showed the absence of lead in the presence of only 160 muM sodium selenite and only 640 muM sodium selenate. The effects of selenium compounds at 80 muM concentration on lead localization in meristematic cells were also investigated. While selenite in garlic cells reduced the number of electron-dense deposits in the cell wall and diminished their size in vacuoles, it increased their number in cytoplasm and plastids, and enlarged them in mitochondria. In pea cells it caused the disappearance of electron-dense sediments from the Golgi apparatus, endoplasmic reticulum, vacuoles and nucleus, or reduced their number in mitochondria, cytoplasm and plastids (lack of large deposits). On the basis of literature data we assume that selenium reduces the lead concentration in Allium sativum and Pisum sativum roots due to the formation of Pb-Se complex in the incubation medium.