Growth and nucleic acid synthesis in synchronously dividing populations of HeLa cells.

Publisher Summary The reproduction of biological systems may be referred to the reproduction of cells Subcellular entities such as viruses cannot maintain themselves indefinitely without parallel reproduction of the cells in which they live The asexual reproduction of organisms such as flatworms is limited by the production of new cells, and all cases of sexual reproduction imply the generation of new cells after the mixing of genetic material from the parent cells An evolutionary consequence of cellularity is implicit in the designation of multicellular organisms as higher organisms Single cells can develop a high level of variety and complexity of structure and function In the development of a multicellular organism, cell division, beginning with the egg, is the essential step toward differentiation If mitosis is a device for the distribution of sister genes to sister cells, the chromosomes may be viewed as a system in which the numerous genes are packaged into a small number of units Mitosis is accompanied by some changes in the physical state or texture of the cytoplasm, which have been assessed as viscosity changes

Mitosis and the Physiology of Cell Division

Synthesis of RNA and protein during mitosis in mammalian tissue culture cells.

It is frequently hypothesised that high soil fungal/bacterial ratios are indicative for more sustainable agricultural systems. Increased F/B ratios have been reported in extensively managed grasslands. To determine the shifts in fungal/bacterial biomass ratio as influenced by grassland management and to find relations with nitrogen leaching potential, we sampled a two-year-old field experiment at an organic experimental farm in the eastern part of The Netherlands. The effect of crop (grass and grass-clover), N application rate (0, 40, 80, ) and manure type (no manure, farm yard manure and slurry) on the F/B ratio within three growing seasons was tested, as well as relations with soil and crop characteristics, nitrate leaching and partial N balance. Biomass of fungi and bacteria was calculated after direct counts using epifluorescence microscopy. Fungal and bacterial biomass and the F/B ratio were higher in grass than in grass-clover. The F/B ratio decreased with increasing N application rate and multiple regression analysis revealed a negative relationship with pH. Bacterial activity (measured as incorporation of [3H]thymidine and [14C]leucine into bacterial DNA and proteins) showed the exact opposite: an increase with N application rate and pH. Leaching increased with N application rate and was higher in grass-clover than in grass. Partial N balance was more positive at a higher N application rate and showed an inverse relationship with fungal biomass and F/B ratio. We conclude that the fungal/bacterial biomass ratio quickly responded to changes in management. Grasslands with higher N input showed lower F/B ratios. Grass-clover had a smaller fungal biomass and higher N leaching than grass. In general, a higher fungal biomass indicated a lower nitrogen leaching and a more negative partial N balance (or smaller N surplus), but more observations are needed to confirm the relationship between F/B ratio and sustainability.

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Fungal/bacterial ratios in grasslands with contrasting nitrogen management

The biological significance of platelet volume: Its relationship to bleeding time, platelet thromboxane B2 production and megakaryocyte nuclear DNA concentration

D.M. Prescott

Papers

Culturing of Amoeba proteus on Tetrahymena.

Variations in the individual generation times of Tetrahymena geleii HS.

Relation between cell growth and cell division. IV. The synthesis of DNA, RNA, and protein from division to division in Tetrahymena.

The nuclear dependence of RNA synthesis in Acanthamoeba sp.

Change in the physiological state of a cell population as a function of culture growth and age (Tetrahymena geleii)