Journal Article

Uptake of Thallium, a Toxic Heavy-Metal, in the Cyanobacterium <i>Synechococcus R-2</i> (Anacystis nidulans, S. Leopoliensis) PCC 7942

Raymond J. Ritchie and A.W.D. Larkum

in Plant and Cell Physiology

Published on behalf of Japanese Society of Plant Physiologists

Volume 39, issue 11, pages 1156-1168
Published in print November 1998 | ISSN: 0032-0781
Published online November 1998 | e-ISSN: 1471-9053 | DOI:
Uptake of Thallium, a Toxic Heavy-Metal, in the Cyanobacterium Synechococcus R-2 (Anacystis nidulans, S. Leopoliensis) PCC 7942

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Uptake of the toxic heavy-metal, thallium, was studied in the cyanobacterium Synechococcus R-2 (PCC 7942) using clinically available 201Tl +. Thallium was found to distribute across the plasmalemma passively, and so the accumulation ratio of the ion ([Tl+]i/[Tl+]o) could be used to calculate the apparent membrane potential (Δ­i,o) of the cells (ETI+i,o = Δ­i,o). The permeability of the plasmalemma to TI+ (PTI+≈ 1 to 5 nms−1) is higher than that of K+. Valinomycin does not increase the permeability of TI+. Transient changes in the Δ­i,o of cells, because of electrogenic transport of ions, could be detected from its effects upon the uptake rate of TI+. HCO3 hyperpolarized Synechococcus cells, whereas NH+4, CH3NH+, and K+ led to depolarization. The use of TI+ as a reporter of Δ­i,o has some inherent limitations. Tl+ is toxic at very low concentrations (inhibitory effects are apparent after about 6 h at concentrations as low as 1 mmol m−3). The rate of equilibration is slow (t1/2≈5 to 20 min). Equilibration of TI+ takes about 2 h, which limits its value as a membrane potential probe. Large amounts of TI+ bind to the surface of the cells making the method impracticable for measuring accumulation ratios of less than about 10 (Δ­i,o) values smaller than about −60 mV). Cultures continuously exposed to Tl+ (10 mmol m−3) eventually become TI+ resistant by actively extruding TI+ (ΔμTI+i,o= −3±0.2 kJ mol−1) and so thallium cannot be used as a Δ­i,o probe in such cells.

Keywords: Cyanobacteria; Electrochemical gradient; Membrane potential; Thallium(I) cation uptake

Journal Article.  0 words. 

Subjects: Biochemistry ; Molecular and Cell Biology ; Plant Sciences and Forestry

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