Dynamics of endogenous levels and subcellular localization of ABA and cytokinins during pollen germination in spruce and tobacco

Protoplasma - We used the enzyme-linked immunosorbent assay (ELISA) to assess the level of endogenous hormones in spruce pollen, and immunolocalization and confocal microscopy to study hormone...     

Determination of Pre- and post-tetanic quantum values in excitatory synapses of CA1 area of hippocampal slices: Application of the deconvolution method

The deconvolution method, i.e., reconstruction of noise-free discrete amplitude distributions of excitatory postsynaptic potentials (EPSPs), has been tested in computer experiments. A generalized quantal model without constraints on distribution of transmitter release probabilities (p) was used. Complex binomial amplitude distributions with a number of discrete components n between 2 and 10 and with different p were simulated. The distance between the discrete components (i.e., the quantum value, v) was determined from simulated distributions with the number of amplitudes N equal to 1000 or 100. For samples with N=100, mean v values were calculated from 10 distributions. The solutions obtained by deconvolution were close to (within ±20% of) the simulated v values when the standard deviation of the noise Sn0.5v. For Sn=0.5–2.0v, v grew in proportion to Sn and was overestimated. A similar correlation was found for v calculated from amplitudes of minimal EPSPs recorded from CA1 area neurons of guinea pig hippocampal slices. However, no significant correlation between v and Sn was found for v>135 µV, i.e., for estimates exceeding the total mean value. A substantial increase in the mean quantal content (m) with a relatively slight increase in v during longterm potentiation (LTP) was confirmed for those cases. Methods of elimination of erroneous v estimates were considered. Rejection of cases with v>2.5Sn (when N=1000) or v>3Sn (when N=100) eliminated erroneous estimates with a high probability but demanded very low noise levels. A new criterion for recognition of correct estimates is suggested. It is based on artificial contamination of the measured amplitudes by the Gaussian noise (noise addition) and on the double-step dependence of v on Sn described above. The solutions selected with this criterion also support a predominant increase of m during LTP with a slight growth of v.Translated from Neirofiziologiya, Vol. 25, No. 2, pp. 84–91, March–April, 1993.     

Negatively charged liposomes as immunological adjuvant for tetanus and diphtheria toxoids

The aim of this study is to develop the previous research on tetanus toxoid and improve the level of antibodies against tetanus and diphtheria toxoids using liposomes as adjuvant. The results show that negatively charged liposomes enhance the immune effects of the combination of the two vaccines.     

Betaine Improves Freezing Tolerance in Wheat

The accumulation of the osmolyte betaine was found to be correlatedwith the development of freezing tolerance (FT) of two wheatcultivars where it increases by about three fold during thecold acclimation period. Exogenous betaine application resultedin a large increase in total osmolality mostly due to betaineaccumulation. Plants that accumulated betaine are more tolerantto freezing stress since a four day exposure to 250 mM betaineresulted in a LT₅₀ of –8°C (in spring wheat Glenlea)and –9°C (in winter wheat Fredrick) compared to –3°C(Glenlea) and –4°C (Fredrick) for control non-exposedplants. Betaine treatment (250 mM) during cold acclimation increasedFT in an additive manner since the LT₅₀ reached –14°C(Glenlea) and –22°C (Fredrick) compared to –8°C(Glenlea) and –16°C (Fredrick) for plants that arecold acclimated in the absence of betaine. These results showthat betaine treatment can improve FT by more than 5°C inboth non-acclimated and cold-acclimated plants. The betainetreatment resulted in the induction of a subset of low temperatureresponsive genes, such as the wcor410, and wcor413, that arealso induced by salinity or drought stresses. In addition tothese genetic responses, betaine treatment was also able toimprove the tolerance to photoin-hibition of PSII and the steady-stateyield of electron transport over PSII in a manner that mimickedcold-acclimated plants. These data also suggest that betaineimproves FT by eliciting some of the genetic and physiologicalresponses associated with cold acclimation. (Received April 23, 1998; Accepted September 4, 1998)     

Sensing environmental temperature change through imbalances between energy supply and energy consumption: Redox state of photosystem II

A basic requirement of all photosynthetic organisms is a balance between overall energy supply through temperature-independent photochemical reactions and energy consumption through the temperature-dependent biochemical reactions of photosynthetic electron transport and contiguous metabolic pathways. Since the turnover of photosystem II (PSII) reaction centers is a limiting step in the conversion of light energy into ATP and NADPH, any energy imbalance may be sensed through modulation of the redox state of PSII. This can be estimated in vivo by chlorophyll a fluorescence as changes in the redox state of PSII, or photosystem II excitation pressure, which reflects changes in the redox poise of intersystem electron transport carriers. Through comparisons of photosynthetic adjustment, we show that growth at low temperature mimics growth at high light. We conclude that terrestrial plants, green algae and cyanobacteria do not respond to changes in growth temperature or growth irradiance per se, but rather, respond to changes in the redox state of intersystem electron transport as reflected by changes in PSII excitation pressure, We suggest that this chloroplastic redox sensing mechanism may be an important component for sensing abiotic stresses in general. Thus, in addition to its role in energy transduction, the chloroplast may also be considered a primary sensor of environmental change through a redox sensing/signalling mechanism that acts synergistically with other signal transduction pathways to elicit the appropriate molecular and physiological responses.     

Genetic Requirements for the Single-Strand Annealing Pathway of Double-Strand Break Repair in Saccharomyces Cerevisiae

HO endonuclease-induced double-strand breaks (DSBs) within a direct duplication of Escherichia coli lacZ genes are repaired either by gene conversion or by single-strand annealing (SSA), with >80% being SSA. Previously it was demonstrated that the RAD52 gene is required for DSB-induced SSA. In the present study, the effects of other genes belonging to the RAD52 epistasis group were analyzed. We show that RAD51, RAD54, RAD55, and RAD57 genes are not required for SSA irrespective of whether recombination occurred in plasmid or chromosomal DNA. In both plasmid and chromosomal constructs with homologous sequences in direct orientation, the proportion of SSA events over gene conversion was significantly elevated in the mutant strains. However, gene conversion was not affected when the two lacZ sequences were in inverted orientation. These results suggest that there is a competition between SSA and gene conversion processes that favors SSA in the absence of RAD51, RAD54, RAD55 and RAD57. Mutations in RAD50 and XRS2 genes do not prevent the completion, but markedly retard the kinetics, of DSB repair by both mechanisms in the lacZ direct repeat plasmid, a result resembling the effects of these genes during mating-type (MAT) switching.     

Developmental changes in the synthesis of nonhistone nuclear proteins relative to the appearance of a short nucleosomal DNA repeat length in cerebral hemisphere neurons

Fluctuations in the pattern of synthesis of nonhistone nuclear proteins were noted in cerebral hemisphere neurons during early postnatal development of the rat. Noteworthy changes included the synthesis of an acidic nuclear protein of relative molecular weight 41,000 (41 K), two chromatin-associated basic proteins (37 K and 38 K) and several high molecular weight chromatin acidic proteins. These changes in the synthesis of nonhistone nuclear proteins occur at a developmental stage when a short nucleosomal DNA repeat length has appeared in cerebral hemisphere neurons.Abbreviations used bp base pairs - DTT dithiothreitol - EDTA ethylenediaminetetraacetic acid - IF isoelectric focusing - PMSF Phenylmethylsulfonylfluoride - SDS sodium dodecyl sulphate     

Interaction of homo-aza-steroidal ester of [p-[bis-(2-chloroethyl) amino]phenyl]acetic acid (ASE) with DNA of Ehrlich ascites tumor cells

A cytostatic, homo-aza-steroidal ester of [p-[bis-(2-chloroethyl) amino]phenyl]acetic acid (ASE) was reduced with NaB³H₄ and [³H]ASE-treated DNA prepared in vitro. We found that: (1) ASE reacts preferentially with purines; (2) ASE decreases the thermal stability of the double helix upon binding to DNA; (3) [³H]ASE binding sites are clustered along the DNA molecules; (4) ASE binding sites probably represent oligo- or polypurine sequences.     

Radiosensitivity of pluripotent stem cells detectable by cloning in the spleen of irradiated mice

It was shown that the dose--effect curves describing the radiosensitivity of CFUc of the bone marrow irradiated in vitro (0.04-3.7 Gy) and treated with normal rabbit serum (NRS) and anti-mouse-brain serum (AMBS) has two differently sloping portions indicating that two CFUc populations differing in radiosensitivity are present in the bone marrow. D0 was 0.93 Gy after irradiation with doses of 0.04-0.75 Gy and treatment with NRS, and 0.33 Gy after incubation of the bone marrow with AMBS. The addition of thymus cells "straightened" the dose--effect curve for the bone marrow treated with AMBS: in this case D0 was 1.81 Gy exceeding considerably the values of D0 for intact bone marrow. The CFUc population is suggested to be heterogeneous in radiosensitivity.     

Possible participation of a free-radical lipid intermediate in the coupling of oxidation and phosphorylation

Data shown propose two regimes of lipid radicals and oxygen utilization realized in mitochondrial membranes. The first one--lipid peroxidation, i.e. interaction of lipid radical and oxygen is an empty step. In switching this regime to the functional one lipid peroxidation is inhibited. Setting L. -dependent coupling apparatus on phosphorylation in mitochondria takes place in the presence of ADP and Pi.