The international society for plant anaerobiosis and its role in opening a new avenue of research

This paper is dedicated to the 35 year jubilee of the founding and the activity of the International Society for Plant Anaerobiosis (ISPA). The role of ISPA members in opening new avenues of research is emphasized. Major developments in the study of plant hypoxic and anoxic stress achieved during subsequent decades are considered. Special attention is given to plant adaptation and damage under conditions of oxygen deficiency and complete absence of oxygen as well as during the post-anaerobic period. Plant metabolic adaptation to anaerobic stress and the capacity of some plants to avoid anaerobiosis are discussed.     

Corticofugal influences on the neurons of different regions of the hypothalamus

Responses of the neurons of the lateral and ventromedial hypothalamic regions (HL andHvm, respectively), as well as of the area of the dorsal hypothalamus (aHd) and the projection region of the medial forelimb bundle (MFB), evoked by stimulation of the proreal cortex (field 8), cingular cortex (field 24), pyriform lobula (periamigdalar cortex), and hippocampus (CA3) were studied in acute experiments on cats under ketamine anesthesia. Distributions of the latent periods of the responses recorded from hypothalamic neurons at stimulation of the above cortical structures were analyzed. The responses were classified into primary excitatory and primary inhibitory. Stimulation of the proreal gyrus evoked four times more excitatory responses than inhibitory responses. With stimulation of the cingular gyrus, the ratio of excitatory/inhibitory responses was 1.5∶1. Stimulation of the pyriform cortex evoked activatory and inhibitory responses with a similar probability. With hippocampal stimulation, inhibitory responses appeared two times more frequently than excitatory reactions. The hypothalamus was found to be a zone of wide convergence: one-half of all responding neurons in theHL andHvm responded to stimulations of two or more tested cortical zones. In 26% of the cells, only excitatory convergence was observed, while in 10% only inhibitory convergence was found; 21% of the cells revealed mixed convergence.     

Pre-steady-state kinetic study of substrate specificity of Escherichia coli formamidopyrimidine--DNA glycosylase

Formamidopyrimidine-DNA glycosylase (Fpg) is responsible for removal of 8-oxoguanine (8-oxoG) and other oxidized purine lesions from DNA and can also excise some oxidatively modified pyrimidines [such as dihydrouracil (DHU)]. Fpg is also specific for a base opposite the lesion, efficiently excising 8-oxoG paired with C but not with A. We have applied stopped-flow kinetics using intrinsic tryptophan fluorescence of the enzyme and fluorescence of 2-aminopurine-labeled DNA to analyze the conformational dynamics of Escherichia coli Fpg during processing of good substrates (8-oxoG.C), poor substrates (8-oxoG.A), and substrates of unclear specificity (such as DHU and 8-oxoG opposite T or G). The analysis of fluorescence traces allows us to conclude that when the enzyme encounters its true substrate, 8-oxoG.C, the complex enters the productive catalytic reaction after approximately 50 ms, partitioning the substrate away from the competing dissociation process, while poor substrates linger in the initial encounter complex for longer. Several intermediate ES complexes were attributed to different structures that exist along the reaction pathway. A likely sequence of events is that the damaged base is first destabilized by the enzyme binding and then everted from DNA, followed by insertion of several amino acid residues into DNA and isomerization of the enzyme into a pre-excision complex. We conclude that rejection of the incorrect substrates occurs mostly at the early stage of formation of the pre-eversion recognition complex, supporting the role of indirect readout in damage recognition.     

Dynamic phase microscopy reveals periodic oscillations of endoplasmic reticulum during network formation

Dynamic phase microscopy was used to study the dynamic events of formation of the endoplasmic reticulum (ER) in interphase-arrested Xenopus egg extract. We have shown that the ER periodically oscillated in an ATP-dependent manner in the frequency range of 1.6–2.2 Hz, while the tubular membrane network formed in vitro. The spectral density, i.e. the pattern of a given frequency component in the Fourier spectrum, was strongly correlated with the dynamic events during microtubule-dependent and microtubule-independent ER network formation observed by video-enhanced contrast differential interference contrast and fluorescence microscopy. Because the 1.6–2.2 Hz frequency of oscillation during the network formation was detected both in the presence and absence of microtubules, it appears to be an intrinsic ATP-dependent ER membrane property. Several characteristic active and inactive stages of ER network formation were observed both in the presence and absence of microtubules. However, data analysis of these stages indicated that microtubules and dynein motor activity have a strong influence and a cooperative effect on the kinetics of ER formation by controlled fusion reaction.     

Visualization of plasma-induced processes by a projection system with a Cu-laser-based brightness amplifier

A novel method for visualization of the process of interaction of high-power energy fluxes with various surfaces is proposed. The possibility of the dynamic visualization of a surface covered with a ∼3-cm-thick plasma layer with a linear density of ∼10¹⁶ cm⁻² is demonstrated experimentally. A scheme of intracavity shadowgraphy of phase objects with the use of a laser projection microscope is developed. Shadow images illustrating the development of the plasma torch of an erosion capillary discharge in air are presented.     

Redox potential of the Rieske iron-sulfur protein: Quantum-chemical and electrostatic study

Quantum-chemical study of structures, energies, and effective partial charge distribution for several models of the Rieske protein redox center is performed in terms of the B3LYP density functional method in combination with the broken symmetry approach using three different atomic basis sets. The structure of the redox complex optimized in vacuum differs markedly from that inside the protein. This means that the protein matrix imposes some stress on the active site resulting in distortion of its structure. The redox potentials calculated for the real active site structure are in a substantially better agreement with the experiment than those calculated for the idealized structure. This shows an important role of the active site distortion in tuning its redox potential. The reference absolute electrode potential of the standard hydrogen electrode is used that accounts for the correction caused by the water surface potential. Electrostatic calculations are performed in the framework of the polarizable solute model. Two dielectric permittivities of the protein are employed: the optical permittivity for calculation of the intraprotein electric field, and the static permittivity for calculation of the dielectric response energy. Only this approach results in a reasonable agreement of the calculated and experimental redox potentials.     

Osmotic water permeability of cell membranes from Mesembryanthemum crystallinum leaves: effects of age and salinity

The osmotic water permeability ( P _os) of cell membranes isolated from leaves of 40-, 50- and 60-day-old Mesembryanthemum crystallinum plants was estimated by measuring light-scattering kinetics using stopped-flow spectrophotometry. The measurements were performed on the plasma membrane (PM), purified tonoplast (TP), and TP-enriched vesicles. The PM and TP-enriched vesicles were obtained by partitioning the microsomal fraction in an aqueous polymer two-phase system, whereas the purified TP vesicles were prepared by microsomal vesicle flotation on a sucrose cushion. The P _os of isolated membranes declined with plant age. The kinetic experiments showed that there was no difference between the P _os of the PM and TP isolated from plants of all ages. A 24-h exposure of plants to 400 m M NaCl caused a decline in the P _os as well. These findings suggest that, during M. crystallinum transition to CAM, which was induced by plant ageing or salinity, plant osmoregulatory responses included changes in the P _os of the leaf-cell membranes. These variations in the P _os are discussed in the context of adaptive mechanisms responsible for the maintenance of the water balance in the common ice plant.     

Long-term hyperthermia impairs activity of both photosystems

This is the first study to perform a simultaneous analysis of the activity of photosystem 1 and photosystem 2 after long-term exposure to elevated temperature. It was found that the quantum yield of photochemical reactions decreases in both photosystems. It is shown that, in photosystem 2, the regulated nonphotochemical quenching decreases whereas the unregulated non-photochemical quenching increases. In photosystem 1, limitation on both acceptor and donor sides increases.     

Molecular mechanisms of antitumor activity of the polymeric form of niclosamide with respect to human colorectal cancer cells

Using poly(lactic-co-glycolic) acid a polymeric form of niclosamide (PFN) has been developed and its antitumor activity against human colorectal cancer cell lines SW837, Caco-2, COLO 320 HSR has been investigated in comparison with free niclosamide. PFN was shown to be more cytotoxic against cancer cells and less cytotoxic against normal cells (human embryonic lung fibroblasts) as compared to niclosamide. Free niclosamide and PFN share a common mechanism of the cytotoxic action on tumor cells, which is associated with mitochondrial damage (evaluated as a decrease in rhodamine 123 accumulation), and increased levels of reactive oxygen species, particularly mitochondrial superoxide anion, causing oxidative damage of intracellular targets. The action of niclosamide and PFN was accompanied by G₀/G₁ cell cycle arrest.