UNSCHEDULED DNA SYNTHESIS INDUCED IN BARLEY SEEDS BY GAMMA RAYS AND 4-NITROQUINOLINE 1-OXIDE
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Abstract:
During the early stage of germination of barley seeds the nuclear chromatin, which was diffused fibrously in the first-leaf and root meristem cells, incorporated tritiated thymidine into them. These tritium-labeled nuclei increased significantly after the treatments of gamma rays and 4-nitro-quinoline 1-oxide (4NQO). With post-treatment of 1mM EDTA, radiation-induced incorporation of tritiated thymidine into the diffuse nuclei of irradiated seeds was inhibited. The results obtained suggest that unscheduled DNA synthesis occurs in accordance with or due to chromatin diffusion in barley cells after gamma-ray irradiation and treatment with 4NQO.Keywords:
4-Nitroquinoline 1-oxide
Thymidine
Thymidine
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The development of higher plants depends on the activity of a shoot apical meristem. Organs are formed on the flanks of the meristem, while pluripotent stem cells are found in a separate domain in the meristem centre. Further domains are distinguished by the expression patterns of genes that control the development of the shoot meristem. Although most plant cells are immobile, their relative position within a meristem, and therefore also their function, can change after cell divisions. To maintain an active shoot meristem throughout plant life, the cells in the meristem need constantly to assess their position, transmit this information to others, and readjust their gene expression profiles and their fate. Some of the genes that permit intercellular communication have been isolated. They enable the flow of information in and between meristem regions via ligands and receptor proteins to transcription factors, that ultimately control the fate of cells in the centre of the meristem. BioEssays 23:134–141, 2001. © 2001 John Wiley & Sons, Inc.
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Tritium from methyl-H3-thymidine was found to be incorporated into proteins in mice. This incorporation in the mouse as a whole represented between 1 and 10% of the injected tritium. Tritiated water was not an intermediate. Transmethylation reactions are proposed as a means whereby certain amino acids might have acquired the tritium from thymidine at some stage of its catabolism. The initial (2 hr) ratios of DNA to protein tritium activities per milligram of wet tissue ranged from 5 in two tissues of low DNA synthetic activity (pancreas, liver) to 35 to 40 in two tissues of high DNA synthetic activity (spleen, small intestine). Labeled nuclear protein was coincident with labeled DNA in nuclei, where it constituted less than 2.5% of the total tritium. The significance of the findings is discussed.
Thymidine
Tritiated water
Catabolism
Specific activity
Transmethylation
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Abstract A study on the intercalary meristems of Triticum aestivum L. and Hordeum vulgare L. — The development, the localization and the organization of intercalary meristems in Triticum aestivum L. and Hordeum vulgare L. have been observed by optical and electron microscope. The shoot meristem is at first an « uninterrupted meristem » (« UM »); then becomes localized at the shoot apex and at the internode base where it forms an « intercalary meristem » (« IM »). Two portions are distinguishable in this last zone: a peripherical one, formed by about ten cell-layers, and an inner one. The cells of these two portions, both in barley and wheat, have cells with different cytological characteristics.
Apex (geometry)
Hordeum
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The reduction of testis mass of the mouse following single injections of tritiated thymidine (1.0–20 wCi tritium/g body mass) or tritiated water (100 microCi tritium/g body mass) and 60Co gamma-rays (delivered to match the dose-rate vs time curve in the 40 wCi tritium/g body mass tritiated water group) was investigated at times from 1 hr to 24 weeks after injection. Measurements of the testicular retention of tritium were also made at these times. There was a progressive loss in mass, up to 30% after 4–5 weeks, followed by an irregular recovery which was more delayed in the case of the tritiated-thymidine-injected animals. The effectiveness of tritium compared with 60Co gamma-rays, calculated using the average absorbed dose to the testis, was 1.43 for tritiated water and 2.07 for tritiated thymidine. A significant effect on the testis mass was seen after the injection of tritiated thymidine at 1.0 microCi tritium/g body mass, which delivered an average absorbed dose to the testis of about 3.5 rad (0.035 Gy) during 16 weeks. Calculations suggest that tritium from tritiated thymidine “fixed” in the testis was about twice as effective as the more labile and uniformly distributed tritium from tritiated water and that in terms of injected amount tritiated thymidine is unlikely to be more than five times as effective as tritiated water even at very low injected amounts.
Tritiated water
Thymidine
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Thymidine
Tritiated water
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Cell fate determination
Root cap
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Hordeum
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Abstract Leaf organogenesis is governed by the spatiotemporal activity of the leaf meristem, which has far greater mitotic activity than the shoot apical meristem. The two types of leaf meristems, the plate meristem and the marginal meristem, are distinguished by the location and longevity of their cell proliferative activity. Most leaf lamina outgrowth depends on the plate meristem. The presence of the marginal meristem was a matter of debate in classic anatomy, but recent genetic analyses of leaf growth in Arabidopsis thaliana confirmed its short-lived activity. Several genes key for the regulation of the two meristem types have been identified, and at least superficially, the systems appear to function independently, as they are regulated by different transcription factors and microRNAs. However, many of the details of these regulatory systems, including how the expression of these key factors is spatially regulated, remain unclear. One major unsolved question is the relationship between the plate meristem and the marginal meristem. Here, I present an overview of our current understanding of this topic and discuss questions that remain to be answered.
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