Available online at www.sciencedirect.com Environmental and Experimental Botany 63 (2008) 416–425 Effects of sodium tungstate on the ultrastructure and growth of pea (Pisum sativum) and cotton (Gossypium hirsutum) seedlings Ioannis-Dimosthenis S. Adamakis a , Eleftherios P. Eleftheriou a,∗ , Thomas L. Rost b a Department of Botany, School of Biology, Aristotle University of Thessaloniki, GR-541 24 Thessaloniki, Greece b Section of Plant Biology, University of California, Davis, CA 95616, USA Received 16 November 2007; accepted 8 December 2007 Abstract Pea (Pisum sativum L. cv. Onmard) and cotton (Gossypium hirsutum L. cv. Campo) seedlings were treated with two concentrations (200 and 500 mg/l) of sodium tungstate (Na 2 WO 4 ) and the developmental effects were investigated. Tungstate retarded seedling growth rate and stopped root elongation in both species. Seedling growth recovered when tungstate was removed, but primary roots continued to be stunted, while lateral root initiation and growth were stimulated. Tungstate induced premature vacuolation in cells of the root apical meristem, with vacuoles having an unusual semi-circular or cap-like shape around the nucleus. In control roots, the nuclei were spherical with prominent nucleoli bearing several randomly distributed fibrillar centres. In the tungstate-treated cells nuclei contained spherical nucleoli with a big nucleolar vacuole. Occasionally, cytoplasmic components, such as mitochondria, were entrapped in the nucleoplasm of interphasic cells of the treated roots. In these roots, most cell plates were fused to only one lateral parental wall suggesting a non-uniform centrifugal extension. The vesicles in these cell plates were dark and fused to each other at a much lower rate than in the dividing cells of the untreated seedlings. Phragmoplast and cortical microtubules were abundant in the untreated cells, but scarcely detected in the treated ones. All these observations are consistent with the view that tungstate causes considerable toxic effects to pea and cotton seedlings. © 2007 Elsevier B.V. All rights reserved. Keywords: Cell plates; Cell vacuolation; Gossypium hirsutum; Nucleolar vacuoles; Pisum sativum; Tungstate 1. Introduction Tungsten (W) is a rare element found chemically bound with other minerals. In the lithosphere, it occurs in small concen- trations ranging from 0.2 to 2.4 mg kg -1 . It is found almost exclusively in the form of tungstates, the chief ones being wolframite [(Fe,Mn)WO 4 ] and stolizite (PbWO 4 ), forming a large number of soluble complexes with a variety of inorganic and organic ligands (Lassner and Schubert, 1999). Anthro- pogenic activities significantly increase tungsten concentration in the environment. Studies in abandoned Portuguese mines have shown that tungsten in soil collected from those sites accumu- lated in the range of 0.8–648 mg kg -1 (Pratas et al., 2005), while phosphate fertilizers may contain tungsten up to 100 mg kg -1 (Senesi et al., 1988). Its high water solubility is of great concern, given that mining activities leave behind vast amounts of spoils ∗ Corresponding author. Tel.: +30 2310 998385; fax: +30 2310 998382. E-mail address: eelefth@bio.auth.gr (E.P. Eleftheriou). and remnants, which may become sources of metal contamina- tion and environmental pollution. These mining processes can degrade cultivated, forest or grazing lands (Wong, 2003). The unique physical and mechanical properties of tungsten such as its high melting/boiling points and density (19.1 g cm -3 ), make it suitable for a variety of applications (see Lassner and Schubert, 1999; Pyatt and Pyatt, 2004). Despite the widespread use and the fact that its toxicity was known as early as 1924 (reviewed by Domingo, 2002), the potential environmental and in particular the biological effects of tungsten have not been thoroughly investigated. Dermatas et al. (2004) and Strigul et al. (2005) have recently studied its effects on environmental sys- tems, including the soil microbial communities. They reported considerable effects in the presence of tungsten, such as reduc- tion in soil respiration and earthworm populations. When applied to strains of Escherichia coli, tungsten compounds were toxico- logically and biologically inert; however, polyoxotungstates had some biological effects (Tajima, 2003). Earlier studies have shown that sodium tungstate (Na 2 WO 4 ) inhibited growth of Anabaena spp. and inactivated nitrogenase 0098-8472/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.envexpbot.2007.12.003