Cessation of cell division

The herbicide dichlobenil (Figure 2.27) is believed to exert its effect through the inhibition of cellulose biosynthesis of actively growing plant tissue, leading to a cessation of cell division and death. 

Adenovirus infection of rapidly growing permissive cells, for example, HeLa cells in suspension culture, leads to the cessation of cell division in 10-12 hr (Green and Daesch, 1961). Nevertheless, such infected cells do continue macromolecular synthesis and have been reported to contain twice the mass, compared to uninfected cells, of DNA and protein by 32 hr after infection (Green and Daesch, 1961 ... 

Given this structural similarity, it should not be surprising to learn that sulfanilamide competes with p-aminobenzoic acid for a binding site on the surface of dihydropteroate synthetase. Put another way, sulfanilamide binds to the enzyme where p-aminobenzoic acid should bind but no reaction occurs. The consequence is that a step in folic acid biosynthesis is disrupted and the bacterial cell is deprived of adequate folic acid. Nucleic acid synthesis, among other things, is disrupted, leading to a cessation of cell growth and division. The human immune system can mop up what remains. No similar consequences befall the human host since it cannot make folic acid in the first place and must get an adequate supply of this vitamin in the diet. 

During the division and enlargement phases of wood cell development, the cell wall is a thin, deformable, and extensible envelope of material referred to as the primary wall. Near the cessation of cell enlargement, however, a secondary wall may begin to be manufactured to the lumen side of the primary wall. Wood fibers, vessel elements, and certain other xylem or phloem elements that function in passive conduction and/or support normally develop a secondary wall (Figure 5). 

In a series of careful studies, the anaesthetic effects of 30 barbiturates on the fertilised eggs and larvae of Arbacia pmctulata were quantitatively determined as a function of extra- and intracellular pH [160], The concentrations of undissociated barbituric acid derivative and its corresponding anion required to produce a 50 per cent reduction in rate of cell division of eggs and cessation of movement of larvae were calculated from the total concentrations of drug, its p/f under the conditions of the experiment, and the pH. The required concentration of undissociated species for a given compound was found to be very nearly constant over the pH range of the experiment, whereas the anion concentration varied considerably. This is exemplified in Table 3.3 for phenobarbitone pK a = 7-26). The results indicate very clearly that the barbiturates penetrate the cells only in the... 

Oxyacetamides and tetrazolinones taken up via the soil provide a strong effect on meristem bearing cell division in the root and shoot tips. Complete arrest of cell division results in cessation of growth and distortion of elongated tissue, leading to plant death. 

Our first investigation of the possible participation of ADPRT activity in cell differentiation used a chick muscle primary cell culture system. When embryonic chick myoblasts are seeded onto collagen-coated petri dishes and grown in a medium containing horse-serum and embryo extract, the majority of the cells pass through an initial phase of proliferation (Fig. 4). The onset of terminal differentiation is marked by the fusion of myoblast cell membranes to form multi-nucleate syncytia of muscle fibres, the cessation of DNA biosynthesis and of cell division. There is also substantial increase in the activity of creatine phosphokinase, largely due to the de novo synthesis of a muscle specific isozyme of this protein. In this work we have made use of... 

The ecdysteroid-responsive Kc permanent cell line was established from disrupted embryos of D. melanogaster [188], Consequently, it is not known what in vivo cell type (if any) they represent. However, the response (aggregation of cells, cessation of division and the formation of axon-like projections) is characteristic and can form the basis of a somewhat time-consuming bioassay [189], which has been used to compare the biological activities of 60 steroids, most of which were inactive. The biological activities of a number of ecdysteroids in this Kc-H cell bioassay are summarised in Table (4). 

Herbicidal sulfonylureas have a unique mode of action they interfere with a key enzyme required for plant cell growth - acetohydroxyacid synthase (AHAS, EC 2.2.1.6) [1, 2, 3] (see also Mark E. Thompson in this volume, Chapter 2.1 Biochemistry of the Target and Resistance ). AHAS is the enzyme responsible for the synthesis of the branched-chain amino acids valine, leucine and isoleucine. Inhibition of this enzyme disrupts the plant s ability to manufacture proteins, and this disruption subsequently leads to the cessation of all cell division and eventual death of the plant. 

Figure 3-13. Percentage of tritium-labeled parietal cells in samples of gastric mucosa of mice after cessation of injection of tritiated thymidine on 4 consecutive days. The number of animals is indicated in parentheses next to the mean and SEM. (From Ragins H, Wincze F, Liu SM, etal. The origin and survival of gastric parietal cells in the mouse. Anat Rec 162 99-110,1968. Reprinted by permission of Wiley-Liss, a division of John Wiley and Sons, Inc.)...

Perhaps the most likely point of cytokinin control of the cell cycle is in G2 or the entry into mitosis from G2. Transfer of cultured soybean cells to cytokinin-free medium leads to cessation of division but not to DNA synthesis, so the amount of DNA per cell approximately doubles (Short et al. 1974). This would not be expected if the cells became blocked at some point preceding S (i.e., at Gi). 

Auxin is essential for cell division in higher plants, but the evidence for direct control of the cell cycle is weaker for auxin than for cytokinin. In tobacco cell suspensions, for example, withdrawal of either cytokinin or auxin leads to cessation of division but, unlike cytokinin, replenishment of auxin has no synchronizing effect on the resumed cell division (Jouanneau 1971). However, auxin does play a role in the timing of cytokinin-induced synchronous division cultures pretreated with auxin before cytokinin restoration begin synchronous cell division earlier than those in which auxin and cytokinin are replenished simultaneously (Peaud-Lenoel and Jouanneau 1971). This indicates that auxin may be necessary, perhaps indirectly, for one or more phases of the cell cycle, possibly the RNA and DNA synthesis associated with the S phase (Nitsch and Lance-Nougarede 1967). 

Cytokinin enhances meiotic cell division in megaspore mother cells of grape (Negi and Olmo 1972). Enhancement of meiosis by cytokinin has also been reported in microspore mother cells of Tradescantia paludosa (Walker and Dietrich 1961). In this case kinetin stimulates the passage of meiotic cells through prophase and, under some conditions, reduces the time between the second meiotic division and the following mitotic division. Prolonged exposure to kinetin, however, causes cessation of meiosis ( meiotic stasis ). 

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