Onion root tips

Micrographs of (A) control, (B) 1,4-cineole-, and (C) 1,8-cineole-treated onion root tip cells, p = prophase, m = metaphase, a = anaphase, and t = telophase. Asterisk indicates formation of a cell plate. (From Romagni, J. G. et al. 2000, J. Chem. Ecol. 23, 303-313. With permission). 

Stiles et al.43 found artemisinin to inhibit respiration in Lemna minor, but the compound strongly stimulates oxygen uptake by lettuce root tips.6 All mitotic phases of onion root tips are inhibited by the compound, and it induces a low level of abnormal mitotic figures.6 Dayan et al.6 conducted a battery of simple physiological tests with several artemisinin analogues. All phytotoxic compounds had similar effects, indicating a common mode of action. In summary, the mode of action results with artemisinin as a phytotoxin are not definitive. 

Colchicine-like mitosis in onion root tip Narcosis of barnacle larvae Narcosis of 2.5-day tadpoles Narcosis of 12-day tadpoles I5o guinea pig ileum 100% inhibition tadpole movement Narcosis of 83-day tadpoles... 

Onion root tip tissue was selected for this purpose,... 

TABLE 6, Types and Frequencies of Chromosomal Aberrations Produced by 2-hr Treatments with Caffeine in Onion Root Tips and in Cell Cultures of the Chinese Hamster ... 

FIGURE 7. Percentages of labeled(L) and unlabeled(U) metaphases with aberrations obtained in onion root tips and in cell cultures of the Chinese hamster various times after 2-hr treatments with 2 X 10 M caffeine and tritiated thymidine. 

Thus, our experiments have shown that the stages sensitive to caffeine are prophase and Gg in onion root tips, and S (and possibly G ) in cell cultures of the Chinese hamster. The aberrations produced are of the... 

Although the types of effects produced by caffeine in hamster cells and in onion root tips are very different, the concentrations needed to produce these effects are about the same in both materials i.e., onion root tips and hamster cells appear to be about equally sensitive to caffeine. On the other hand, we have found that 8-ethoxycaffeine, which is much more active than caffeine in plant roots (e.g., Kihlman, 1952), has about the same activity as caffeine in hamster cells. 

In repeated studies in vitro, cycasin was nonmutagenic. In addition to being carcinogenic, methylazoxymethanol, the metabolite of cycasin, was found to be mutagenic for S, typhimurium (Smith, 1966), to cause chromosome aberrations in onion root tip cells, and to increase sex-linked recessive lethal mutations in Drosophila (Smith, 1966 Teas and Sax, 1966). In studies with G-46, cycasin was not active in vitro, while the metabolite MAM was mutagenic (Gabridge et aL, 19696). 

It is this latter hypothesis as to the biological function of M-rays that has remained controversial to the present day. Gurwitsch used onion root tips and later yeast cells and measured an increase in mitotic figures in the former and an increased rate of growth in the latter (Gurvitsch, 1932 ... 

Chromosome aberrations CHO cells Onion root tips Simple phenols phenolic acids cinnamic acids Chlorogenic acid Several phenolics Stich et al. (1981a) Stich et al. (1981b) Levan and Tjio (1948)... 

In apical meristems of Vicia faba roots, lAA increases the duration of S with no change in the initial rate of DNA synthesis (Webster 1967). This indicates that the effects of lAA on S, as with the previously-mentioned effects of cytokinins on S, are not by an overall modification of DNA synthesis. This is supported by the data of Nagl (1972) showing that total suppression of mitosis by lAA in onion root tips occurs with no inhibition of DNA replication. 

Asulam (Figure 5.19) is a benzenesulfonyl carbamate, and its mode of action was originally proposed to be similar to that of N-phenylcarba-mates. Onion root tip cells treated with asulam become arrested in metaphase, suggesting interference with MT assembly or function (Section 5.4 and Ref. 152). 

Matsumoto, S.T. Mantovani, M.S. Malaguttii, M.I.A. Dias, A.L. Fonseca, I.C. Marin-Morales, M.A. 2006. Genotoxicity and mutagenicity of water contaminated with tannery effluents, as evaluated by the mieronueleus test and eomet assay using the fish Oreochromis niloticus and ehromosome aberrations in onion root-tips. Genetics and Molecular Biology, v.29, p. 148-158. 

A number of workers have reported rapid changes in the content of cellular RNA following cytokinin treatment kinetin application can double the RNA level of onion root tip cells within 30 min. Associated with these changes, the cytokinins increase or alter the... 

Many phytotoxins are mitotic inhibitors. However, the effects are seldom due to direct effects on the mitotic apparatus. Onion (Allium cepa L.) seeds are germinated in the presence of the natural products under a 14-h photoperiod.6 Root tips are prepared according to Armbruster et al.,2 and mitotic analysis is performed with a compound microscrope on 1000 cells per slide (three slides per treatment).6 9137 In addition to the proportions of cells in each stage of mitosis, the number of abnormal mitotic figures should be determined. 

Higher plants have been used in tests for genotoxicity that are discussed in more detail in Section 7.3.3. For example, the onion Allium cepa has been used not only in root elongation assays for toxicity but to detect mitotic, cytoki-netic, and chromosomal aberration in the root tips (Fiskesjo 1995). A micronucleus assay that detects chromosome breaks in Tradescantia sp. planted in areas suspected of pollution has been used (Sandhu et al. 1991) and suggests the possible value of such assays in the terrestrial environment or as an indicator of atmospheric pollution. 

CDAA (N-N-diallyl-2-chloroacetamide) was reported to reduce mitosis in barley (Hordeum vulgare L.) roots nearly 90% after 96 h at 57 yM (38). Propachlor (2-chloro-N-isopropylacetanilide) totally inhibited mitosis in onion (Allium cepa L.) root tips after an 18 h treatment with 75 yM (3 ). At 20 yM cell division was reduced approximately 50% and cell enlargement was reduced 40% in oat coleoptiles (39). After 24 h, 100 yM ioxynil (4-hydroxy-3,5-diiodobenzonitrile) reduced the mitotic index in broad bean (Vicia faba L. ) and pea root tips ( ). Few herbicides that inhibit cell division have been studied in adequate detail to locate the site of the block. A notable exception is the herbicide chlorsulfuron (DPX 4189, 2-chloro-N- [(4-methoxy-6-methyl-l,3,5-triazin-2-yl)amino]carbonyl -benzenesulfonamide) ( ). Ray reported a 50% reduction in corn growth 3 h after treatment with 28 yM chlorsulfuron. Mitosis in broad bean root tips was significantly reduced by 2.8 yM, whereas in three different tests, cell enlargement was not influenced with concentrations of 28 yM. Thymidine incorporation into DNA was inhibited in corn root tips after a 1 h treatment with... 

FIGURE L Chromosome complements in root tips A) the horse bean, Vida faba B) the tree onion, Allium proliferum (C) the common onion, Allium cepa. Acetic alcohol, Feulgen squash. 

Since the tree onion is propagated vegetatively, the material is genetically uniform. The root-tip chromosomes of the tree onion are shown in Fig. IB. Their number is the same as that of A, cepa, viz., 16, and they are of about the same size as the cepa chromosomes. However, the proliferum chromosomes are easier to identify than those of A. cepa. In proliferum the chromosomes do not form identical pairs. Thus, the root-tip cells of A. proliferum have only one satellite chromosome, which has a larger satellite and a shorter short arm than the pair of satellite chromosomes in A. cepa. (This satellite chromosome is, in fact, very similar to those of A. fistulosum, which supports the suggestion that the tree onion is more closely related to A. fistulosum than to A. cepa.)... 

The experiments performed in my laboratory with onion A. proliferum) root tips and cell cultures of the Chinese hamster as experimental material have confirmed the striking differences between the effects of caffeine in root tips and mammalian cells. 

Seven day old pregerminated onion seeds were preincubated with pyrenocine A at various concentrations or for various durations. Pretreated seedlings were rinsed with water, 1 cm root tips excised and then incubated in the presence of 14C-acetate for 1 h. Chloroplasts were incubated in the simultaneous presence of acetate and pyrenocine for 1 h. All other methods are described elsewhere (3,4). 

Fig. 2.22. Transverse section (EM) through the wall of epidermal cell of an onion root the cell was situated about 1 mm from the tip. The arrow points towards the centre of the cell. The scale corresponds to 1 /it. (By courtesy of G. Setterfield and S. T. Bayley, Canad.J. Bat., 35 435, 1957.)...

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