Phytotoxicity of nanoparticles: Inhibition of seed germination and root growth

Contamination of soils by heavy metals is of widespread occurrence as a result of human, agricultural and industrial activities. Among heavy metals, lead is a potential pollutant that readily accumulates in soils and sediments. Although lead is not an essential element for plants, it gets easily absorbed and accumulated in different plant parts. Uptake of Pb in plants is regulated by pH, particle size and cation exchange capacity of the soils as well as by root exudation and other physico-chemical parameters. Excess Pb causes a number of toxicity symptoms in plants e.g. stunted growth, chlorosis and blackening of root system. Pb inhibits photosynthesis, upsets mineral nutrition and water balance, changes hormonal status and affects membrane structure and permeability. This review addresses various morphological, physiological and biochemical effects of Pb toxicity and also strategies adopted by plants for Pb-detoxification and developing tolerance to Pb. Mechanisms of Pb-detoxification include sequestration of Pb in the vacuole, phytochelatin synthesis and binding to glutathione and aminoacids etc. Pb tolerance is associated with the capacity of plants to restrict Pb to the cell walls, synthesis of osmolytes and activation of antioxidant defense system. Remediation of soils contaminated with Pb using phytoremediation and rhizofiltration technologies appear to have great potential for cleaning of Pb-contaminated soils.

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Lead toxicity in plants

Carbon nanotubes (CNTs) were found to penetrate tomato seeds and affect their germination and growth rates. The germination was found to be dramatically higher for seeds that germinated on medium containing CNTs (10−40 μg/mL) compared to control. Analytical methods indicated that the CNTs are able to penetrate the thick seed coat and support water uptake inside seeds, a process which can affect seed germination and growth of tomato seedlings.

Carbon nanotubes are able to penetrate plant seed coat and dramatically affect seed germination and plant growth.

High metal availability, arising from mining and industrial activities, disposal of sewage sludge or soil acidification, is an increasing problem in agriculture and forestry. Metal toxicity causes multiple direct and indirect effects in plants which concern practically all physiological functions. In this review we consider the effects of excess heavy metals and aluminium on those functions which will alter plant water relations. After a brief comment on the metal effects in cell walls and plasmalemma, and their consequences for cell expansion growth, the influences of high metal availability on the factors which regulate water entry and water exit in plants are considered. Emphasis is placed on the importance of distinguishing between low water availability in mine and serpentine soils and toxicity effects in plants which may impair the regulation of a plant's water household. Examples on water relations of both plants grown on metalliferous soil and hydroponics are discussed. The effects of met...

Plant water relations as affected by heavy metal stress: A review

The biochemistry of environmental heavy metal uptake by plants: implications for the food chain.

The effect of lead on seed imbibition and germination in different plant species

Comparison of lead tolerance in Allium cepa with other plant species

Lead migrating through the tissues of Allium cepa L. was found, by electron microscopy, autoradiography and other methods, to encounter at least three barriers to penetration. The layers of protoderm and hypodermic meristematic cells in the root meristematic zone and the layer of endodermis in the mature root zone were barriers to apoplastic transport. The central zone was a barrier to apoplastic and symplastic transport. It comprises the quiescent centre in the root meristem and the central part of the root cap. The cells of the deepest ground meristematic tissue layers seemed to act as a barrier, which keeps lead away from the procambium. Lead accumulated in roots but it was not uniformly distributed between their various tissues. The largest amount of lead accumulated both in ground meristematic and cortex tissues.

Lead accumulation and its translocation barriers in roots of Allium cepa L.-autoradiographic and ultrastructural studies.

The adaptation of Silene vulgaris to growth on a calamine waste heap (S. Poland)

Plants of Dianthus carthusianorum from a calamine (zinc–lead) waste heap and from unpolluted stands were compared in the field and under controlled laboratory conditions It was found that the waste-heap plants differed significantly from those in the normal population in respect to the following morphological traits: lower weight of aerial parts, shorter and narrower leaves, smaller number of leaves per plant In combination with shorter, less numerous shoots, these features reduce the transpiration area of the plants The general habit (predominance of forms with short and trailing shoots) of the waste-heap population points to adaptation to a xeric environment Under controlled conditions all of the above traits were maintained through three successive generations They are thus genetically controlled Root tolerance tests showed that the waste-heap plants had higher tolerance to zinc and lead These results indicate that strong selection processes have generated a clear ecotypical differentiation for heavy metal tolerance and drought tolerance in a zinc–lead-rich waste-heap population of D carthusianorum (variety)

M. Wierzbicka

Papers

The effect of lead on seed imbibition and germination in different plant species

Comparison of lead tolerance in Allium cepa with other plant species

Lead accumulation and its translocation barriers in roots of Allium cepa L.-autoradiographic and ultrastructural studies.

The adaptation of Silene vulgaris to growth on a calamine waste heap (S. Poland)

The adaptation of Dianthus carthusianorum L. ( Caryophyllaceae ) to growth on a zinc–lead heap in southern Poland