Chlorophyll fluorescence in the leaves of Tradescantia species of different ecological groups: Induction events at different intensities of actinic light

Chlorophyll fluorescence analysis is one of the most convenient and widespread techniques used to monitor photosynthesis performance in plants. In this work, after a brief overview of the mechanisms of regulation of photosynthetic electron transport and protection of photosynthetic apparatus against photodamage, we describe results of our study of the effects of actinic light intensity on photosynthetic performance in Tradescantia species of different ecological groups. Using the chlorophyll fluorescence as a probe of photosynthetic activity, we have found that the shade-tolerant species Tradescantia fluminensis shows a higher sensitivity to short-term illumination (≤20 min) with low and moderate light (≤200 μE m⁻² s⁻¹) as compared with the light-resistant species Tradescantia sillamontana. In T. fluminensis, non-photochemical quenching of chlorophyll fluorescence (NPQ) and photosystem II operational efficiency (parameter Φ_PSII) saturate as soon as actinic light reaches ≈200 μE m⁻² s⁻¹. Otherwise, T. sillamontana revealed a higher capacity for NPQ at strong light (≥800 μE m⁻² s⁻¹). The post-illumination adaptation of shade-tolerant plants occurs slower than in the light-resistant species. The data obtained are discussed in terms of reactivity of photosynthetic apparatus to short-term variations of the environment light.     

Plant virus infection development as affected by heavy metal stress

The work was focused on the investigation of possible dependencies between the development of viral infection in plants and the presence of high heavy metal concentrations in soil. Field experiments have been conducted in order to study the development of systemic tobacco mosaic virus (TMV) infection in Lycopersicon esculentum L. cv. Miliana plants under effect of separate salts of heavy metals Cu, Zn and Pb deposited in soil. As it is shown, simultaneous effect of viral infection and heavy metals in tenfold maximum permissible concentration leads to decrease of total chlorophyll content in experiment plants mainly due to the degradation of chlorophyll a. The reduction of chlorophyll concentration under the combined influence of both stress factors was more serious comparing to the separate effect of every single factor. Plants' treatment with toxic concentrations of lead and zinc leaded to slight delay in the development of systemic TMV infection together with more than twofold increase of virus content in plants that may be an evidence of synergism between these heavy metal's and virus' effects. Contrary, copper although decreased total chlorophyll content but showed protective properties and significantly reduced amount of virus in plants.     

Biophysical Methods of Ecological Monitoring. Photosynthetic characteristics of tree plants growing in Moscow city

In this work, we studied the influence of ecological factors (distance from thoroughfares) on photosynthetic characteristics of leaves of four tree species growing in Moscow city. Photosynthetic activity of leaves was assayed by instrumental methods of probing the functional state of the photosynthetic apparatus, using electron paramagnetic resonance for measuring the kinetics of photooxidation of P₇₀₀ centers, thermoluminescence, and slow induction of chlorophyll fluorescence. It has been shown that the kinetic parameters of the induction curves, as determined from the kinetics of P₇₀₀ photooxidation and slow fluorescence induction in dark-adapted leaves, are sensitive to variations of plant growth conditions. These parameters can be used as informative characteristics in ecological monitoring.     

Ion channels of glutamate receptors: structural modeling

Ionotropic glutamate receptors belong to the superfamily of P-loop channels as well as K⁺, Na⁺, and Ca²⁺ channels. However, the structural similarity between ion channels of the glutamate receptors and K⁺ channels is a matter of discussion. The aim of this study was to analyze differences between the structures of K⁺ channels and glutamate receptor channels. For this purpose, homology models of NMDA and AMPA receptor channels (M2 and M3 segments) were built using X-ray structures of K⁺ channels as templates. The models were optimized and used to reproduce specific data on the structure of glutamate receptor channels. Particular attention was paid to the data of the binding of channel blockers and to the results of scanning mutagenesis. The modeling demonstrates that properties of glutamate receptor channel can be reproduced assuming only local structural deformations of the K⁺ channel templates. The most valuable differences were found in the selectivity-filter region, whereas helical parts of M2 and M3 segments could have similar spatial organization with homologous segments in K⁺ channels. It is concluded that the current experimental data on glutamate receptor channels does not reveal global structural differences with K⁺ channels.     

Irreversible block of cardiac mutant Na+ channels by batrachotoxin

Batrachotoxin (BTX) not only keeps the voltage-gated Na(+) channel open persistently but also reduces its single-channel conductance. Although a BTX receptor has been delimited within the inner cavity of Na(+) channels, how Na(+) ions flow through the BTX-bound permeation pathway remains unclear. In this report we tested a hypothesis that Na(+) ions traverse a narrow gap between bound BTX and residue N927 at D2S6 of cardiac hNa(v)1.5 Na(+) channels. We found that BTX at 5 microM indeed elicited a strong block of hNa(v)1.5-N927K currents (approximately 70%) after 1000 repetitive pulses (+50 mV/20 ms at 2 Hz) without any effects on Na(+) channel gating. Once occurred, this unique use-dependent block of hNa(v)1.5-N927K Na(+) channels recovered little at holding potential (-140 mV), demonstrating that BTX block is irreversible under our experimental conditions. Such an irreversible effect likewise developed in fast inactivation-deficient hNa(v)1.5-N927K Na(+) channels albeit with a faster on-rate; approximately 90% of peak Na(+) currents were abolished by BTX after 200 repetitive pulses (+50 mV/20 ms). This use-dependent block of fast inactivation-deficient hNa(v)1.5-N927K Na(+) channels by BTX was duration dependent. The longer the pulse duration the larger the block developed. Among N927K/W/R/H/D/S/Q/G/E substitutions in fast inactivation-deficient hNa(v)1.5 Na(+) channels, only N927K/R Na(+) currents were highly sensitive to BTX block. We conclude that (a) BTX binds within the inner cavity and partly occludes the permeation pathway and (b) residue hNa(v)1.5-N927 is critical for ion permeation between bound BTX and D2S6, probably because the side-chain of N927 helps coordinate permeating Na(+) ions.     

Slow induction of chlorophyll a fluorescence excited by blue and red light in Tradescantia leaves acclimated to high and low light

Photosynthesis Research - Tradescantia is a good model for assaying induction events in higher plant leaves. Chlorophyll (Chl) fluorescence serves as a sensitive reporter of the functional state of...     

The enzyme-antienzyme interactions of a number of Burkholderia pseudomallei hydrolases with monoclonal immunoglobulins

Phosphatase, phospholipase C and a proteolytic complex, including casein- and hemoglobin-hydrolases, have been isolated from cell-free extracts of B. pseudomallei cultivation medium. A set of monoclonal antibodies (McAb) to the antigenic complexes of this infective agent has been obtained. Conditions for the study of the interaction of the enzymes and McAb have been worked out, and most of the 14 immunoglobulins under study have been shown to neutralize 2-3 hydrolases each. Three types of McAb, selectively inhibiting only the proteolytic complex, only casein-hydrolase and only phospholipase C, have been identified.     

Random walk analysis of restricted metabolite diffusion in skeletal myofibril systems

The purpose of this work was the development of a basal mathematical model for the diffusion of low-molecular metabolites in a skeletal muscle cell. A three-dimension diffusion of low-molecular particles was simulated by a Monte-Carlo method (random walks of diffusing molecules). The model takes into account the following structural elements: (i) a regular lattice of actin and myosin filaments inside a myofibril; (ii) the membranes of sarcoplasmic reticulum and mitochondria surrounding the myofibrils; (iii) a set of myofibrils inside a skeletal muscle cell. We simulated diffusion of particles in the bulk of intracellular water phase and their reflections from the rigid surfaces of intracellular structures. The model allowed to calculate the apparent coefficients of particle diffusion in the axial and radial directions, Dparallel(app) and Dperpendicular(app), respectively. In accordance with experimental data from literature, the coefficient Dparallel(app) was independent of time. The coefficient of radial diffusion Dperpendicular(app) decreased with time to steady state values similar to that determined by the NMR diffusion spectroscopy methods. The interactions of diffusing particles with thin and thick filaments of myofibrils could explain the decrease in the Dperpendicular(app) value by a factor of 20%. The collisions of particles with myofilaments began to reveal themselves as a gradual decrease in the Dperpendicular(app) value at early stages of diffusion (t1/2 approximately equal to 0.05 microsec). The contribution of particle reflections from the membranes of sarcoplasmic reticulum and mitochondria to the retardation of the radial diffusion was about of 20-30%, depending on porosity of a membranous shield around the myofibril. For conventional sizes of a membranous shield (diameter 2 microm), the interactions of particles with the shield caused a decrease in the Dperpendicular(app) value with a half-time t1/2 approximately equal to 0.5 msec. This time is essentially lower by a factor about of 100 than that found in published NMR measurements. When we considered diffusion of particles inside a cell compartment confined to impermeable membranous shield, the reflection of particles from this shield led the drastic decrease in the radial diffusion coefficient (Dperpendicular(app) --> porportional to when t --> porportional to). This pattern of the Dperpendicular(app)(t) time-course might be expected in the NMR measurements on skeletal muscle tissue where a sarcolemma represents an impermeable shield for ATP and PCr molecules.