Journal of Hazardous Materials 161 (2009) 463–473 Contents lists available at ScienceDirect Journal of Hazardous Materials journal homepage: www.elsevier.com/locate/jhazmat Cadmium-induced functional and ultrastructural alterations in roots of two transgenic cotton cultivars M.K. Daud a , Yuqiang Sun a , M. Dawood a , Y. Hayat b , M.T. Variath a , Yu-Xiang Wu a , Raziuddin a,c , Ullah Mishkat d , Salahuddin e , Ullah Najeeb a , Shuijin Zhu a,∗ a Department of Agronomy, College of Agriculture and Biotechnology, Zhejiang University, Hangzhou 310029, PR China b Institute of Bioinformatics, Zhejiang University, Hangzhou 310029, PR China c Plant Breeding and Genetics Department, NWFP Agricultural University Peshawar, Peshawar, Pakistan d Zoological Sciences Division, Pakistan Museum of Natural History, Garden Avenue, Shakarparian, Islamabad 44000, Pakistan e District Agriculture Extension Offices, Bannu Road, Dera Ismail Khan (NWFP), Pakistan article info Article history: Received 25 November 2007 Received in revised form 27 March 2008 Accepted 27 March 2008 Available online 7 April 2008 Keywords: Transgenic cotton Cadmium stress Electron microscopy Root morphology Gossypium spp. abstract The toxic effect of cadmium (Cd) at increasing concentrations was studied with special attention being given to the root morphological and ultrastructural changes in two transgenic cotton cultivars viz. BR001 and GK30 and their wild relative viz. Coker 312. In comparison to their respective controls, low concen- tration (10 and 100 M) of Cd greatly stimulated seed germination, while it was inhibited by highest concentration of Cd (1000 M) in case of two transgenic cultivars. However, in Coker 312 the seed ger- mination percentage progressively decreased over the control at all Cd levels. Various physiological and morphological parameters of the root and whole plant in both transgenic cotton cultivars and their relative wild cotton genotype respond differently towards the Cd toxicity. Bioavailability of Cd was concentration- dependent where seedling root captured more Cd as compared to shoot. BR001 accumulated more Cd followed by GK30, while Coker 312 was less Cd accumulator. The ultrastructural modifications in the root tip cells of both the transgenic cotton cultivars and their wild relative were also dose-dependent. With the increase in Cd levels, the fine structures of their root cells also invariably changed. Increase in plas- molysis of the plasma membrane, greater number of nucleoli and vacuoles and enlarged vacuoles could be observed in both transgenic cotton cultivars. In comparison to them, Coker 312 showed relatively well developed ultrastructures of the root tips except enlarged vacuoles and greater number of mitochondria. Moreover, the accumulation of Cd in the form of electron dense granules and crystals both in vacuoles and attached to cell walls were visible in both transgenic cotton cultivars and their wild relative. These results suggest that both transgenic cotton cultivars and their wild relative cotton genotype responded positively towards Cd stress at seedling stage, the internal Cd-detoxification might be through apoplastic and symplastic binding. Moreover, as a whole BR001 proved to be sensitive whereas; GK30 and Coker 312 were found as tolerant. © 2008 Elsevier B.V. All rights reserved. 1. Introduction Cadmium (Cd) is an extremely significant pollutant due to its high toxicity and large solubility in water. It is wide spread in environment as a result of various anthropogenic activities [1,2] and has been mostly a “guest” metal in Pb:Zn mineralization because it never occurs in isolation in the natural environments [3]. Typically, the non-polluted soil contains Cd in the range of 0.04–0.32 mM, while moderately and highly polluted soils reach up to 0.32–1.00 mM Cd [4,5]. By virtue of its chemical and physi- ∗ Corresponding author. Tel.: +86 571 81703758; fax: +86 571 86971117. E-mail address: shjzhu@zju.edu.cn (S. Zhu). cal similarity to essential cations such as Fe, Cu, and Zn, Cd uptake in plants can be facilitated by the uptake systems of these cations [6–9]. Although having no known biological function [10], Cd can alter physiological and morphological features of both plants and animals. In plants, anatomic and structural changes are known to be some of the worst effects of Cd [11,12]. Liu et al. [13] and Shah and Dubey [14] found the occurrence of low mitotic index and pyc- nosis, cell division and cell proliferation, chromosomal aberrations, alteration in the synthesis of RNA and slowing down of ribonucle- ase activity in various crops. Moreover, an increase in the number of nucleoli and vacuoles, condensation of cytoplasm, reduction of mitochondrial cristae, severe plasmolysis, highly condensed chromatin materials, enlargement of vacuoles, disorganization of chloroplast structure, and disruption of nuclear envelope, plas- 0304-3894/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.jhazmat.2008.03.128