NMR study of the structural transition in the DNA-bound water system in the interval of physiological temperatures

Temperature dependence of spin-spin proton relaxation times of DNA and bound water and the content of bound water in the samples of DNA, saturated with water in the atmosphere with different relative humidities from 0 to 100% were studied by means of pulsed NMR. It is shown that the temperature transition in the system of DNA-bound water in the interval 18-35 degrees is observed only when the relative humidity is more than 70% and the double-stranded structure of DNA exists. The transition of DNA from one conformation into another passes through some intermediate state more labile and probably less ordered. This transition is accompanied by changes in the structure of the hydration shell. In the case when relative humidity is greater than 80%, the partial dehydration of DNA stimulated by the transition is observed. This dehydration increases with the increase of relative humidity.     

A new dimension to observations in minirhizotrons: A stereoscopic view on root photographs

Summary With a stereoscope, as used for the inspection of aerial photographs, sequential photographs of roots obtained by the endoscope method from minirhizotrons can yield much more information than hitherto. A series of photographs shows that most of the roots seen in a minirhizotron in grassland grew on the surface of the lexan tube, while there was a gap between the roots and the soil. Decay of the extensive root hair zones around the roots may make new root growth in the gap between rhizotron wall and soil invisible. Some consequences of these observations for the endoscope method are discussed.     

Mathematical modeling of the dynamics of the intensity of the mutation process. II. Dynamic evaluation of the frequencies of hereditary pathology

Mathematical models were devised to evaluate the dynamics of hereditary pathology frequencies, based on registration of spontaneous abortions, congenital malformations and Down disease in the city of Angarsk during 12 years. The models provide an opportunity to detect the fact of the presence or absence of temporary tendencies. The average frequency of spontaneous abortions and units of hereditary pathology have not been changed for 12 years, the frequency of Down disease being decreased, while congenital malformations seem to change with certain periodicity. In cases of insufficient sample sizes, the prolongation of observation for a period of several years does not facilitate the task of construction of models which could adequately describe multifactor-conditioned processes.     

Permeability and damage of the erythrocyte membrane at -1 degree C to -9 degrees C shown by the NMR relaxation method

Amount of inter--and extracellular unfrozen water in the intact human erythrocytes as well as tau a, "a life time" of water molecules in these cells, have been determined. The progressive compression of the erythrocytes during freezing them as deep as -5 degrees C has been found to submit to the ideal osmometer law. The membrane impermeability to Mn2+ ions has been disturbed when the temperature falls to -7 degrees C and below, the erythrocytes reaching "the minimal volume".     

Foliicole flechten aus zaire (III) Die GattungByssoloma Trevisan

Nine species ofByssoloma Trevisan (Pilocarpaceae) are reported from a collection of foliicolous lichens from Zaire, and includeB. murinum sp. n. In addition,B. usambarense sp. n. is described from adjacent Tanzania. A determination key is provided to all the known African species, and each species is briefly characterized.     

Modification of the lipid composition of neuroblastoma C1300 cells using liposomes

An essential increase in the total cholesterol content with a significant growth in the level of its esters was observed in neuroblastoma C1300 cells differentiated by means of 5'-bromodesoxyuridine and incubated for 1 h with lecithin-cholesterol liposomes (1:1 mol/mol). These cells also displayed an increased amount of polyunsaturated fatty acids in the composition of lecithin molecules and the appearance of lysolicethin as well. Incubation of the cells with lecithin liposomes was accompanied by a decrease in the content of cholincholesterol in the cells. In this case the level of cholesterol esters decreased to a greater extent than the level of free cholesterol. In lecithin molecules of these cells there occurred a relative increase of saturated fatty acids. The cells can retain viability and compensate changes caused by cholesterol excess during their incubation with lecithin-cholesterol liposome for 60-90 min. A longer incubation with liposomes results in a sharp drop of cell viability.     

Transient state characteristics of adaptation to changes in light conditions for the cyanobacterium Oscillatoria agardhii

Transitions in growth irradiance level from 92 to 7 Em^-2 s^-1 and vice versa caused changes in the pigment contents and photosynthesis of Oscillatoria agardhii. The changes in chlorophyll a and C-phycocyanin contents during the transition from high to low irradiance (HL) were reflected in photosynthetic parameters. In the LH transition light utilization efficiencies of the cells changed faster than pigment contents. This appeared to be related to the lowering of light utilization efficiencies of photosynthesis. As a possible explanation it was hypothesized that excess photosynthate production led to feed back inhibition of photosynthesis. Time-scales of changes in the maximal rate of O₂ evolution were discussed as changes in the number of reaction centers of photosystem II in relation to photosynthetic electron transport. Parameters that were subject to change during irradiance transitions obeyed first order kinetics, but hysteresis occurred when comparing HL with LH transients. Interpretation of first order kinetic analysis was discussed in terms of adaptive response vs changes in growth rate.Non-standard abbreviations Chla chlorophyll a - CPC C-phycocyanin - PS II photosystem II - PS I photosystem I - RC II reaction center of photosystem II - P photosynthetic O₂-evolution - I irradiance, Em^-2 s^-1 - light utilization efficiency of cells, mmol O₂·mg dry wt^-1·h^-1/Em^-2 s^-1 - light utilization efficiency of photosynthetic apparatus, mol O₂·mol Chla ^-1·h^-1/Em^-2 s^-1 - P_max maximal rate of O₂ evolution by cells, mol O₂·mg dry wt^-1·h^-1 - P_max maximal rate of O₂ evolution by photosynthetic apparatus, mol O₂·mol·Chla ^-1·h^-1 - LL low light, E m^-2 s^-1 - HL high light, E m^-2 s^-1 - LH low to high light transition - HL high to low light transition - k specific rate of adaptation, h^-1 - specific growth rate, h^-1 - Q pool size of cell constituent, mol·mg dry wt^-1 - q net synthesis rate of cell constituent, mol·mg dry wt^-1·h^-1     

Membrane model of the regulation of proliferation: the theory and interpretation of an experiment

The role of cell surface physical organization in the cell cycle regulation is analyzed within the framework of the earlier proposed theory (Chernavskii et al., 1982). Two models of cell surface are considered: hard-frame fluid-mosaic model (latticemosaic) and the fluid-mosaic one. The former deals with normal cells. The existence of integral carcasse or "frame" which is formed by the essential part of cross-linked membrane components and may have at least two different conformational states is hypothesized. The second model describes membranes of tumour cells. With the latter theory any mitogen (excluding the restoration of nutrient depletion) reduces the mechanical tensile strength of the frame and stimulates the general structural rearrangement of the plasma membrane. There are only two conformational transitions during the cell cycle which serve as signals for the beginning of S and M phases. If the values of tensile strength are great enough and therefore the conformational transitions are impossible, the cells pass into the resting (prereplicative--G01, or premitotical--G02) state. Three types of experiments are interpreted in the proposed theory: a) on differences in the action of growth factors on normal and tumour cell cycle, b) on the necessary condition for mitogenicity of lectins, c) on the stimulation of proliferation by mechanical deformation of cells.     

Effect of postsynaptic blockade of neuromuscualar transmission on properties of the frog fast muscle fiber membrane

Sensitivity of the postsynpatic membrane to acetylcholine, the resting membrane potential, input resistance, and membrane time constant of fast muscle fibers were measured in experiments on frogs. Complete immobilization of the animals with D-tubocurarine or local immobilization of a muscle with α-bungarotoxin was found not to affect these parameters of the muscle membrane, whereas denervation of the muscle widens the zone of postsynaptic sensitivity to acetylcholine, lowers the resting membrane potential, and increases the input resistance and time constant of the muscle membrane. These results are evidence that neurotrophic control of the frog fast muscle fiber membrane is achieved mainly by substances reaching the muscle via axoplasmic transport and not by the character of the neuronal discharge and motor activity or by synaptic acetylcholine.