Mixotrophy in microorganisms: Ecological and cytophysiological aspects

Mixotrophy is the ability to combine autotrophic and heterotrophic modes of nutrition. It is widely spread in a variety of microorganisms including such important plankton groups as dinoflagellates and cyanobacteria. In marine ecosystems, mixotrophy complicates our concept of the flow of materials and energy and therefore has been thoroughly studied for recent decades. Nevertheless, the exact data on the auto/heterotrophy balance during mixotrophic growth are still lacking, mainly due to insufficient knowledge of physiological and molecular grounds of this phenomenon. In this review, we address the ecological and cytophysiological aspects of the problem of mixotrophy in microorganisms as well as discuss possible causes of the relatively slow progress in this field.     

Toxicological aspects of metallothionein.

Metallothionein (MT) is expressed to a certain extent in almost all mammalian tissues. The biological significance of MT is related to its various forms MT-1, MT-2, MT-3 and MT4. For MT-1 several isoforms of the protein exist and it is likely that these isoforms are related to various functions involved in developmental processes occurring at various stages of gestation. Toxicokinetics and biochemistry of essential and toxic metals such as cadmium, zinc, mercury and copper in organs e.g. kidney, CNS, are often related to metallothionein. It is debated whether there is a relation or not for other metals e.g. selenium and bismuth. For the toxicokinetics of cadmium, MT plays an important role. By expanding techniques from experimental toxicology and biochemistry to include molecular biology methods, more specific and relevant studies can be performed of the actual role and biological function of MT. The present paper on toxicological aspects of metallothionein, presents an overview and evaluation of present knowledge concerning differences among organs and within organs of the expression of MT and how this affects tissue sensitivity to toxicity.     

Structural and energetic aspects of spin pairing in lanthanides

Numerical Hartree-Fock calculations on the lanthanide ions confirm the earlier results of Marcantonatos and coworkers, by showing that the excitation from the ground state of a given fⁿ- configuration to a state with lower spin multiplicity is accompanied by a change in size and shape of the orbitals. This orbital change is also shown to be at the basis of a new interpretation of the spin pairing phenomenon in lanthanides. This interpretation is significantly different from the picture offered by conventional multiplet theory; indeed, the spin pairing energy, calculated on the basis of Hartree- Fock theory is accompanied by a decrease in interelectronic repulsion.Although the relevant energetic (repulsion) effects are obviously quite large, the underlying size effects are very much smaller. Therefore, it seems highly unlikely that they are responsible for the change in coordination number of Gd(H₂O)₈³⁺ upon excitation, as suggested by Marcantonatos.     

Pollen hydration status at dispersal: cytophysiological features and strategies

Summary The aim of this paper is to draw attention to partially hydrated pollen, namely, pollen grains having a high water content (>30%); this type of pollen is more frequent than previously thought. Various cyto-physiological strategies are used to retain water during exposure and dispersal such as cytoplasm carbohydrates; in the absence of such strategies, fast pollination must be ensured, because uncontrolled loss of water leads to pollen death. On the other hand, a state of partial hydration allows a fast tube emission (even within 3–5 min). Several methods for determining the hydration status of pollen at anthesis are proposed.     

Effect of UV-B radiation on cytophysiological responses in plants

Solar UV-B radiation reaching the Earth's surface is continually increased due to the stratospheric ozone layer depletion. UV-B radiation has been shown to have mutagenic effects damaging DNA, proteins and membranes. During evolution plants developed systems for UV-B perception and effective defense mechanisms. In this review the main UV-B effects, cytophysiological responses of plants and their interactions with microorganisms are analyzed. UV-B-induced signal transduction pathways in plant cells are discussed.     

Energetic aspects of propagation of action potential

On the basis of the electrical analogue of an action potential suggested previously, the distribution of electrical field outside and inside the membrane was obtained. The energy released upon the propagation of a single action potential along the nerve fibre was calculated. A comparison of the results with the available data showed the correctness of the calculations performed.     

Physicochemical aspects of the antiseptic action of nanohydroxyapatite

The mechanism of interaction of nanocrystals of hydroxyapatite with Staphylococcus aureus bacteria has been investigated. It was shown that the growth of bacteria and their colonies both in the presence and absence of hydroxyapatite nanocrystals can be described using the Fokker-Planck equation. It was found that hydroxyapatite nanocrystals adhere in a particular orientation on the surface of bacteria, decreasing substantially their colony-forming ability.     

Hemodynamic aspects of the hypotensive action of captopril

Captopril was tested in acute experiments on anesthetized cats subject to cardiopulmonary bypass. The drug was shown to reduce total peripheral vascular resistance and to increase vascular bed capacity.     

In vitro cytochemical and cytophysiological study of in vivo activated mouse peritoneal macrophages

The morphological, cytochemical (acid phosphatase activity) and cytophysiological (phagocytosis) features of mouse peritoneal macrophages activated in vivo by two bacterial agents. Corynebacterium parvum parvum and Polidin, were investigated in vitro. Both immunostimulants induced an increase in cytochemical and phagocytic activities of the activated peritoneal macrophages but in different degrees, the changes being more extensive in the case of Corynebacterium parvum-activated macrophages.     

Genetic aspects of the immunomodulating action of interferon

The data of the study of alpha/beta interferon (IFN) effect in mice of different genotype were presented. CBA mice of H-2k genotype, C57B1/6 mice of H-2b genotype and their hybrid (CBA X C57B1/6) F1 have been used in the experiments. IFN has been injected intraperitoneally in a dose of 100-5000 U/mouse in combination with antigenic stimulation. It was shown that IFN enhanced stem cells migration from bone marrow in CBA, but not in (CBA X C57B1/6)F1 mice. At the same time the splenocytes from CBA mice were more sensitive to inhibition by IFN than splenocytes from C57B1/6 mice. This was found in antibody and immune rosette-formation tests. The effect of IFN on the immune system cells is probably predetermined by the individual genetic characteristics of a mouse strain.     

Biochemical aspects of the action of local anesthetics

Notions on the molecular mechanisms of anesthesia are presented. The chemical characteristics are given for main representatives of certain groups of local anesthetics with peculiarities of their membrane-tropic action mentioned. The effect of local anesthetics on the synaptic transmission, membrane enzymes, ion transport through the cell membranes is considered simultaneously with the anesthesia phenomenon on the basis of the data available in literature and results of the authors' investigations.