同位素示踪技术在光合作用研究中的应用

利用同位素示踪技术可以掌握物质在化学反应中运行和变化情况。试论述同位素示踪技术在研究光合作用中的多种应用：提示光合作用中几种元素的转变方向;判断光合作用的反应场所和反应条件;推断光合作用的反应过程;检验产物的运输方向;研究光合作用与呼吸作用的关系。     

Physiological aspects of apoptosis

Study of apoptosis is a new stage in development of biomedical sciences. At the cellular level the process is realised on account of efferents supporting an equilibrium among proliferation, differentiation, and programmed cell death. Significance of each of the factors is determined by its role in physiological systems functioning. Cell death infringement may cause pathological conditions and diseases followed by both degenerative and proliferative changes.     

Physiological and pathophysiological aspects of ceramide

Activation of cells by receptor- and nonreceptor-mediated stimuli not only requires a change in the activity of signaling proteins but also requires a reorganization of the topology of the signalosom in the cell. The cell membrane contains distinct domains, rafts that serve the spatial organization of signaling molecules in the cell. Many receptors or stress stimuli transform rafts by the generation of ceramide. These stimuli activate the acid sphingomyelinase and induce a translocation of this enzyme onto the extracellular leaflet of the cell membrane. Surface acid sphingomyelinase generates ceramide that serves to fuse small rafts and to form large ceramide-enriched membrane platforms. These platforms cluster receptor molecules, recruit intracellular signaling molecules to aggregated receptors, and seem to exclude inhibitory signaling factors. Thus ceramide-enriched membrane platforms do not seem to be part of a specific signaling pathway but may facilitate and amplify the specific signaling elicited by the cognate stimulus. This general function may enable these membrane domains to be critically involved in the induction of apoptosis by death receptors and stress stimuli, bacterial and viral infections of mammalian cells, and the regulation of cardiovascular functions.     

Physiological aspects of conjugation in fission yeast

Summary Conjugation was studied in Schizosaccharomyces pombe using liquid media. Nitrogen, which was growth-limiting in a synthetic medium, had to be consumed completely before conjugation could start. Conjugation was preceded by sexual agglutination. Agglutinability was not constitutive in heterothallic strains. It only developed when cells of h ⁺ and h ^- mating type were grown in mixed culture for at least 2.5 hr before the start of conjugation.     

Physiological regulation of carbon fixation in the photosynthesis and calcification of coccolithophorids

Emiliania huxleyi and Gephyrocapsa oceanica are the predominant coccolithophorid species that produce blooms in the ocean and affect the global environment. These species are capable of carbon fixation by both photosynthesis for organic matter production and by intracellular calcification for coccolith production. Both processes were strongly affected by the nutrient status in a laboratory culture. The coccolith production was stimulated by the addition of a high concentration of sodium bicarbonate and by the depletion of phosphate. Interestingly, when the calcification was stimulated, the increase in cell number during algal growth was greatly suppressed and then the cell volume increased. When the growth rate was increased under nutrient-sufficient conditions, the cells became very small in size and most of them bore few or no coccoliths. The data from laboratory experiments show that the cell growth and calcification proceeded apparently independently at different phases. We, therefore, assume that the coccolithophorid blooms in the ocean might be separated into two phases; firstly, the increase in cell population might be triggered by an adequate supply of nutrients to enhance algal growth and then the calcification might subsequently be stimulated when the nutrients become depleted by substantial algal growth.     

Physiological and molecular aspects of salt stress in plants

The study of salt stress mechanisms in plants has become an important issue for the modern agricultural development, climate change, and global food crisis. The plant response to high salt concentrations is complex and comprehensive; it includes many different processes, which should be correctly coordinated. The effect of excessive salt concentrations on plants results in osmotic stress and creates an ionic inbalance due to the accumulation of toxic ions, such as Cl^? and, especially, Na⁺. Salt stress also has negative impact on mineral homeostasis, in particular Ca²⁺ and K⁺. The progress in transcryptomics, genomics, and molecular biology revealed a new gene families that participate in the formation of salt stress response in plants. This review describes the fundamental principles and mechanisms of plant salt tolerance, maintenance of ion homeostasis. In this paper the detailed analysis of the maine transport membrane systems responsible for the transport of ions and their role in plant salt stress were conducted. The perspectives and directions for the further biotechnological and genetic improvement of salt tolerance in plants are underlied.     

Physiological aspects on catecholamine sampling

Catecholamine (CA) determinations are valuable tools in studies of sympatho-adrenal activity. However, several methodological problems should be considered when designing experiments and interpreting plasma CA results. The commonly assessed antecubital venous noradrenaline (NA) concentrations reflect local nerve activity, since about half of this NA is derived from the forearm tissues. Sympathetic nerve activity is not uniform, but may vary considerably between organs. Overall sympathetic activity is best assessed by measurements of NA in arterial or mixed venous blood. Venous adrenaline (ADR) levels may also be unrepresentative due to marked and variable extraction in the peripheral tissues. Urinary NA and ADR excretion studies still provide valuable information. Regional studies of NA overflow from individual organs give good estimates of local nerve activity and will increase the understanding of the functional organization of the sympathetic nervous system.