Characterization of Cu and Zn Resistant Nicotiana plumbaginifolia Suspension Cultures

The mechanisms of Cu and Zn resistance in cultured Nicotianaplumbaginifolia cells were investigated. When crude extractsof both the Cu and Zn resistant cells were passed through SephadexG-75 gel filtration columns, two metal containing peaks wereidentified. In each case the Cu or Zn was associated with ahigh molecular weight fraction (ca. 70,000) and a low molecularweight fraction (less than 3,000) with the majority being associatedwith the low molecular weight fraction. The low molecular weightfraction in particular increased upon exposure of the cellsto the metals. Both the Cu and Zn resistant cells accumulated higher levelsof citrate and malate than the wild type cells in the presenceof the metals. The addition of citrate or malate, but not fumarateor succinate to the culture medium prevented Cu or Zn toxicityto wild type cells. These results suggest that the N. plumbaginifoliacells selected as resistant to Cu or Zn are resistant, at leastin part, because of their ability to accumulate the chelators,citrate and malate, in the presence of the metals. ¹Present address: Plantech Research Institute, MCI ResearchCenter, 1000 Kamoshida-cho, Midoriku, Yokohama 227 Japan (Received June 30, 1986; Accepted December 1, 1986)