Functional plasticity of photosynthetic apparatus and its resistance to photoinhibition in <Emphasis Type="Italic">Plantago media</Emphasis>

Morphological and functional characteristics of Plantago media L. leaves were compared for plants growing at different light regimes on limestone outcrops in Southern Timan (62°45′N, 55°49′E). The plants grown in open areas under exposure to full sunlight had small leaves with low pigment content and high specific leaf weight; these leaves exhibited high photosynthetic capacity and elevated water use efficiency at high irradiance. The maximum photochemical activity of photosystem II (F _v/F _m) in leaves of sun plants remained at the level of about 0.8 throughout the day. The photosynthetic apparatus of sun plants was resistant to excess photosynthetically active radiation, mostly due to non-photochemical quenching of chlorophyll fluorescence (qN). This quenching was promoted by elevated deepoxiation of violaxanthin cycle pigments. Accumulation of zeaxanthin, a photoprotective pigment in sun plant leaves was observed already in the morning hours. The plant leaves grown in the shade of dense herbage were significantly larger than the sun leaves, with pigment content 1.5–2.0 times greater than in sun leaves; these leaves had low qN values and did not need extensive deepoxidation of violaxanthin cycle pigments. The data reveal the morphophysiological plasticity of plantain plants in relation to lighting regime. Environmental conditions can facilitate the formation of the ecotype with photosynthetic apparatus resistant to photoinhibition. Owing to this adjustment, hoary plantain plants are capable of surviving in ecotopes with high insolation.     

Comparative evaluation of morphofunctional organization of vertebrate nuclear blood cells

Morphometrical parameters, osmoregulatory possibilities, and the membrane reserve value of nuclear hemocytes (leukocytes and erythrocytes) were studied in the main classes of vertebrates by using method of hypoosmotic loads. It has been established that in the fish--mammals line in erythrocytes the absolute reserve of the plasmalemma decreases and the relative area of the cell surface increases. Evolution of leukocytes is accompanied by an increase of the membrane reserve and of the surface area due to a decrease of volume and to a rise of folding of the plasmalemma.     

Ryanodine does not produce negative chronotropic effect on action potential generation in heart pacemaker cells of young frogs Rana temporaria

The goal of the present work consisted in studying role of Ca²⁺ released via ryanodine-sensitive receptors of the sarcoplasmic reticulum in modulation of frequency of action potential (AP) generation of cells of the pacemaker type of the young and adult frog heart. Ryanodine (3 μM) decreased the AP generation frequency in adult frogs by 43%, while produced no effect in young animals. Duration of the diastolic depolarization decreased more than twice as compared with control. Ryanodine (20 μM) inhibited completely the AP generation spontaneous activity in adult frogs, whereas in young animals the negative chronotropic effect was observed, on average, by 14%. The rate of diastolic depolarization did not change. Based on analysis of our obtained data and the literature data, we have concluded that in young frogs there takes place the spatial-temporal uncoupling of the sarcoplasmic reticulum and the sarcolemmal membrane. Original Russian Text ? V. F. Golovko, 2006, published in Zhurnal Evolyutsionnoi Biokhimii i Fiziologii, 2006, Vol. 42, No. 4, pp. 335–339.     

The Effects of Ion Channel Inhibitors on the Generation of Electrical Impulses in Right Atrial Pacemaker Cells of 10-Day-Old Chicken Embryos

Biophysics - The cellular mechanisms of pacemaker-cell activity and the contribution of various ion channels of the embryonic heart are not yet fully understood. This paper presents the results of...     

Effects of GABA antagonist-induced seizures on 3H-muscimol and 3H-diazepam binding in the rat striatum]

The binding of 3H-muscimol and 3H-diazepam to rat striatum membranes after picrotoxin- and bicuculline-induced seizures was characterized. No alteration in the maximal binding capacity (Bmax) of 3H-muscimol was observed. However, bicuculline produced a 27% decrease in Kd. Both picrotoxin and bicuculline increased the binding capacity of 3H-diazepam. Bicuculline produced a 86% increase in Kd. These results suggest that the GABA antagonists-induced seizures may modulate 3H-muscimol and 3H-diazepam binding in rat striatum.     

3H-tert-butylbicyclo-ortho-benzoate--a new ligand for chloride ion channel of GABA-A receptor]

The study was made of the binding of 35S-t-butylbicyclophosphorothionate and 3H-t-butylbicycloorthobenzoate (TBOB) which label a GABAA receptor-regulated chloride ionophores to glass fiber filters GF/B and GF/C. The rate of 3H-TBOB binding was higher. GABA displayed a biphasic effect on 3H-TBOB binding to rat brain synaptic membrane; enhancement at low concentrations of the agent and inhibition at higher ones. The results suggest that GABA may modulate the 3H-TBOB binding.     

The Effect of Light Regime on Source–Sink Relations in the Shade-Enduring Ajuga reptans Plant

A quantitative approach to the evaluation of source–sink relations in Ajuga reptans plants grown under the forest canopy (shade plants) and on an open plot (sun plants) was worked out in terms of growth characteristics, CO₂ exchange, and carbon balance. Shade plants developed leaves with the relative and specific areas twice exceeding those of sun plants. Sun plants assimilated more carbon, using a significant part of it for the development of numerous runners. During a day, shade and sun plants produced 0.03 and 0.67 g of substrate, respectively. At the same time, forest (shade) plants spent 48% of assimilates for the respiration, in comparison with plants from the open plot that spent almost 70% of assimilates for respiration as they were greater in size. It was concluded, that light controls source–sink relations, which is a way of realization of the life strategy and a coordination mechanism of functional integrity of the plant organism. Light not only controls photosynthesis (source activity) but morphophysiological characteristics of plants with their hierarchical structure of sinks too.     

Deltosides from Allium nutans L

Steroid glicoside which structure was elucidated by using mass-spectroscopic and NMR techniques, has been isolated using column chromatography on reverse-phase silicagel (C-18) from underground parts of Allium nutans. This compounds for the first time was isolated from the plants of genus Allium.