Micronucleus Assay with Tetrad Cells of Tradescantia.

The Tradescantia micronucleus assay has been used since 50 years for the detection of genotoxins (including carcinogens) in the environment. A large database concerning the effects of individual chemicals and complex environmental mixtures (soil, air and waters) has accumulated. In contrast to other mutagenicity test systems, the effects of low concentrations of heavy metals, radionuclides, certain herbicides, pesticides and gaseous mutagens can be detected and it is also possible to conduct in situ biomonitoring studies with plant. The test system has been validated and standardized protocols have been developed for laboratory experiments and for field studies which are described in this chapter.

Micronucleus assay with tetrad cells of Tradescantia.

The Tradescantia micronucleus assay is being used since almost 50 years for the detection of genotoxins (including carcinogens) in the environment. A large database on the effects of individual compounds and of complex environmental mixtures (soil, air and water) has accumulated. In contrast to other mutagenicity test systems, the effects of low concentrations of heavy metals, radionuclides, certain herbicides and pesticides, and gaseous mutagens can be detected and it is also possible to use the test for in situ biomonitoring studies. The test system has been validated, and standardized protocols have been developed for laboratory experiments and for field studies, which are described in this chapter.

Cell-to-cell transport via the lumen of the endoplasmic reticulum.

Plasmodesmata are plasma membrane-lined channels through which cytoplasmic molecules move from cell-to-cell in plants. Most plasmodesmata contain a desmotubule, a central tube of endoplasmic reticulum (ER), that connects the ER of adjacent cells. Here we demonstrate that molecules of up to 10.4 kDa in size can move between the ER lumen of neighbouring leaf trichome or epidermal cells via the desmotubule lumen. Fluorescent molecules of up to 10 kDa, microinjected into the ER of Nicotiana trichome cells, consistently moved into the ER and nuclei of neighbouring trichome cells. This movement occurred more rapidly than movement via the cytoplasmic pathway. A fluorescent 3-kDa dextran microinjected into the ER of a basal trichome cell moved into the ER and nuclei of epidermal cells across a barrier to cytoplasmic movement. We constructed a 10.4-kDa recombinant ER-lumenal reporter protein (LRP) from a fragment of the endogenous ER-lumenal binding protein AtBIP1. Following transient expression of the LRP in the ER of Tradescantia leaf epidermal cells, it often moved into the nuclear envelopes of neighbouring cells. However, green fluorescent protein targeted to the ER lumen (ER-GFP) did not move from cell to cell. We propose that the ER lumen of plant cells is continuous with that of their neighbours, and allows movement of small ER-lumenal molecules between cells.

Micronucleus assays with Tradescantia pollen tetrads: an update.

Micronucleus (MN) assays with early pollen tetrad cells of Tradescantia (Trad-MN assays) are at present the most widely used bioassays with plants for the detection of genotoxins in the environment. So far, ∼ 160 chemicals have been tested and ∼ 100 articles that concern complex environmental mixtures were published. This article summarises the results of Trad-MN studies, which have been carried out during the last 15 years with individual compounds and investigations concerning the pollution of environmental compartments (soil, water and air). The evaluation shows that the effects of certain genotoxins such as heavy metals, radionuclides, pesticides and air pollutants can be easily detected with this test. Comparisons with results obtained in MN studies with mitotic (root tip) cells indicate that meiotic tetrad cells are in general more sensitive. Important issues for future research concern the evaluation of the suitability of wildlife Tradescantia species that are sometimes used instead of specific clones (such as #4430 for which standardised protocols have been developed) as well as the assessment of the predictive value of Trad-MN results in regard to the prediction of cancer hazards in humans and adverse effects at the ecosystem level. The fact that the genotoxic effects of certain compound such as metals, which can be detected with plant bioassays, in particular with the Trad-MN assay but not in other commonly used bioassays (e.g. in bacterial tests) makes them an essential element in the batteries for environmental monitoring.