Response to cadmium in higher plants

Heavy metal contamination of soil and water causing toxicity/stress has become one important constraint to crop productivity and quality. This situation has further worsened by the increasing population growth and inherent food demand. It have been reported in several studies that counterbalancing toxicity, due to heavy metal requires complex mechanisms at molecular, biochemical, physiological, cellular, tissue and whole plant level, which might manifest in terms of improved crop productivity. Recent advances in various disciplines of biological sciences such as metabolomics, transcriptomics, proteomics etc. have assisted in the characterization of metabolites, transcription factors, stress-inducible proteins involved in heavy metal tolerance, which in turn can be utilized for generating heavy metal tolerant crops. This review summarizes various tolerance strategies of plants under heavy metal toxicity, covering the role of metabolites (metabolomics), trace elements (ionomics), transcription factors (transcriptomics), various stress-inducible proteins (proteomics) as well as the role of plant hormones. We also provide a glance at strategies adopted by metal accumulating plants also known as “metallophytes”.

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Heavy Metal Tolerance in Plants: Role of Transcriptomics, Proteomics, Metabolomics, and Ionomics.

http://repository.ias.ac.in/38950/1/1-Pub.pdf

Comparison of mercury, lead and arsenic with respect to genotoxic effects on plant systems and the development of genetic tolerance

Aluminum is the major element in the soil and exists as a stable complex with oxygen and silicate in neutral and weakly acidic soil. When the soil pH is lower than 4.5-5.0, Al is solubilized in the soil water and absorbed by plant roots. Absorbed Al inhibits root elongation severely, and the elongation of roots exposed to Al3+ as low as mumol level is inhibited within an hour(s). Thus much research has been conducted to understand the mechanism of Al toxicity and tolerance. Al is located specifically at the root apex. Al-sensitive plants absorb more Al than do Al-tolerant plants, and thus the exclusion mechanism of Al is the major idea for Al tolerance. The understanding of Al stress in plants is important for stable food production in future. Al is a complicated ion in its chemical form and biological function. In this chapter, mechanisms of Al toxicity and tolerance proposed during the past few decades as well as future topics are described from physiological and molecular points of view.

Cell biology of aluminum toxicity and tolerance in higher plants.

Using the examples of cadmium and lead, the review considers the various toxic effects exerted by these heavy metals. Putative specific and nonspecific mechanisms of the toxic effects of the heavy metals and plant responses are discussed together with the issue of Cd and Pb accumulation in various plant organelles, cells, tissues, and organs. The basic mechanisms providing for plant resistance to excess Cd and Pb are elucidated. These data are used to schematically outline the changes in plant metabolism produced by these heavy metals.

Physiological Aspects of Cadmium and Lead Toxic Effects on Higher Plants

Effects of lead on root growth, cell division, and nucleolus of Allium cepa

The effects of trivalent and hexavalent chromium on root growth, cell division and chromosome morphology of Allium cepa were studied. The concentrations used of chromium nitrate and potassium dichromate were 2 × 10-1, 2 × 10-2, 2 × 10-3, 2 × 10-4, 2 × 10-5, 2 × 10-6, and 2 × 10-7M. The results showed that both trivalent and hexavalent chromium inhibit root growth and cause mitotic irregularities comprising c-mitosis, anaphase bridges, chromosome stickiness, and chromosome fragmentation and lagging. When compared with chromium nitrate on the equimolar basis, potassium dichromate showed a stronger inhibitory and toxic effect on root growth and cell division, respectively. The possible mechanism of the Cr poisoning of root meristem cells of Allium cepa is also briefly discussed.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1601-5223.1992.tb00003.x

Effects of trivalent and hexavalent chromium on root growth and cell division of Allium cepa

The effects of different concentrations of eleven different metals (aluminum chloride, chromium nitrate and potassium dichromate, lead nitrate, copper sulfate, manganous sulfate, cobaltous nitrate, zinc sulfate, magnesium sulfate, nickel sulfate, cadmium chloride, and mercuric chloride) on cell division and nucleoli in root tip cells of Allium cepa were studied. The results showed that the metal ions could, in varying degrees, cause chromosome, nucleus, and nucleolus irregularities, including c-mitosis, chromosome bridges, chromosome stickiness, irregularly shaped nuclei, micronuclei, irregularly shaped nucleoli, some silver-stained material scattered in the nucleus, the weakening of silver-staining reaction at the periphery of the nucleolus, and the release of nucleolar material from the nucleus into the cytoplasm. The Allium test may be useful for the rapid screening of chemicals involved in environmental problems.

Evaluation of metal ion toxicity on root tip cells by the allium test

The effects of different concentrations (10−5 – 10−2 M) of copper sulfate on root growth, cell division and nucleoli in root tip cells of Zea mays L. were investigated. 10−5 M Cu stimulated root growth, but at higher concentrations (10−4 – 10−2 M) inhibited it. Cu had toxic effects on chromosomal morphology: c-mitosis, anaphase bridges, and chromosome stickiness were induced. Some nuclei had irregular shape and particles extruded from nucleoli to nuclei and finally from the nuclei into the cytoplasm.

Effects of Pb 2+ on Root Growth, Cell Division, and Nucleolus of Zea mays L.

The effects of different concentrations of aluminium chloride on the nucleoli in root tip cells of Allium cepa were studied using the silver staining technique. The concentrations used of aluminium chloride (AlCl3) were 1.0 × 10-5, 5.0 × 10 -5, 1.0 × 10 4, 5.0 × 10 4, 1.0 × 10-3, 5.0 × 10-3, 1.0 × 10-2, 5.0 × 10-2, and 1.0 × 10-1 M. After the treatment with Al3+, the nucleolar material was extruded from the nucleus into the cytoplasm. The phenomenon was observed in both the inner root meristem cells and the root cap cells. But there were differences between the two regarding the shape and position of the silver-stained material in the cytoplasm. The present observations with the silver staining technique confirm the phenomenon observed for the first time by FlSKRSJO (1983). The possible mechanism behind this phenomenon is also briefly discussed.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1601-5223.1992.tb00564.x

Donghua Liu

Papers

Effects of lead on root growth, cell division, and nucleolus of Allium cepa

Effects of trivalent and hexavalent chromium on root growth and cell division of Allium cepa

Evaluation of metal ion toxicity on root tip cells by the allium test

Effects of Pb 2+ on Root Growth, Cell Division, and Nucleolus of Zea mays L.

Effects of Al3+ on the nucleolus in root tip cells of Allium cepa