Effects of hexavalent chromium on microtubule organization, ER distribution and callose deposition in root tip cells of Allium cepa L.

Abstract

The subcellular targets of hexavalent chromium [Cr(VI)] were examined in Allium cepa root tips with confocal laser scanning microscopy. Cr(VI) exerted dose- and time-dependent negative effects on root growth rate, the mitotic index and microtubule (MT) organization during cell division cycle. Interphase MTs were more resistant than the mitotic ones, but when affected they were shorter, sparse and disoriented. The preprophase band of MTs became poorly organized, branched or with fragmented MTs, whilst neither a perinuclear array nor a prophase spindle was formed. Metaphase spindles converged to eccentric mini poles or consisted of dissimilar halves and were unable to correctly orient the chromosomes. Anaphase spindles were less disturbed, but chromatids failed to separate; neither did they move to the poles. At telophase, projecting, lagging or bridging chromosomes and micronuclei also occurred. Phragmoplasts were unilaterally developed, split, located at unexpected sites and frequently dissociated from the branched and misaligned cell plates. Chromosomal aberrations were directly correlated with MT disturbance. The morphology and distribution of endoplasmic reticulum was severely perturbed and presumably contributed to MT disassembly. Heavy callose apposition was also induced by Cr(VI), maybe in the context of a cellular defence reaction. Results indicate that MTs are one of the main subcellular targets of Cr(VI), MT impairment underlies chromosomal and mitotic aberrations, and MTs may constitute a reliable biomonitoring system for Cr(VI) toxicity in plants.

Chromium (VI) Uptake and Tolerance Potential in Cotton Cultivars: Effect on Their Root Physiology, Ultramorphology, and Oxidative Metabolism

“…Increase in number of nuclei and vacuolar size and its number as well as the presence of Cr dense precipitates in the dead parts of the cell in all these cultivars shows a positive indication that they can be used for phytoremediation purpose in Cr-contaminated areas. Consistent with our results, Panda [22] in rice seedlings, Speranza et al [50] in the pollen grains of kiwi, and Eleftheriou et al [51] in Allium cepa observed almost similar ultramorphological features in Cr-treated root samples.…”

Hexavalent chromium-induced differential disruption of cortical microtubules in some Fabaceae species is correlated with acetylation of α-tubulin

“…MT effect is a less explored parameter (Fusconi et al 2007). In the present study, we show that MTs of five Fabaceae species constitute a prime subcellular target of Cr(VI) toxicity, thus substantiating the notion that MTs could be a universal target of Cr(VI) toxicity (Eleftheriou et al 2012. The universality of MT targeting by tungsten, another heavy metal belonging to the same group (VI-B) of the periodic table of elements along with Cr, was shown in taxonomically diverse land plant taxa representing monocots, dicots, gymnosperms, pterophytes, and bryophytes (Adamakis et al 2010b).…”

“…More recently, differential effects of Cr(VI) in two unrelated plant species were reported. In A. cepa, cortical MTs were extensively fragmented and depolymerized (Eleftheriou et al 2012). Similarly, cortical MTs of V. faba herewith examined were depolymerized and disappeared after prolonged treatment with Cr(VI).…”

“…Research has also been conducted on the cytotoxic, genotoxic, and ultrastructural attributes of Cr in plants (e.g., Qian 2004;Panda 2007;Rodriguez et al 2011), but few have focused on Cr(VI) effects to MT cytoskeleton of plants (Eleftheriou et al 2012(Eleftheriou et al , 2015. In particular, Cr(VI) was found to disturb the mitosis of root tip cells by different mechanisms: in A. cepa (Alliaceae) by depolymerizing MTs (Eleftheriou et al 2012), while in Lens culinaris (Fabaceae) by stabilizing them . Moreover, MT stabilization in L. culinaris was accompanied by a time-and concentration-dependent increase of acetylated α-tubulin, which is considered as an indicator of MT stabilization (Webster and Borisy 1989;Perdiz et al 2011).…”

Copper‐induced root growth inhibition of Allium cepa var. agrogarum L. involves disturbances in cell division and DNA damage

“…Several studies have shown that microtubules are very sensitive to stress conditions and that the array and synthesis of microtubules can be influenced by temperature, drugs, or metal ions [9,32]. Several studies have shown that microtubules are very sensitive to stress conditions and that the array and synthesis of microtubules can be influenced by temperature, drugs, or metal ions [9,32].…”