The species specific response of photosystem 2 (PS2) efficiency and its thermotolerance to diurnal and seasonal alterations in leaf temperature, irradiance, and water relations were investigated under alpine field conditions (1 950 m) and in response to an in situ long-term heat treatment (+3 K). Three plant species were compared using the naturally occurring microstratification of alpine environments, i.e. under contrasting leaf temperatures but under similar macroclimatic conditions. Thermotolerance of PS2 showed a high variability in all three species of up to 9.6 K. Diumal changes (increases or even decreases) in PS2 thermotolerance occurred frequently with a maximum increase of +4.8 K in Loiseleuria procumbens. Increasing leaf temperatures and photosynthetic photon flux density influenced thermotolerance adjustments. Under long-term heating (+3 K) of L. procumbens canopies with infra-red lamps, the maxima of the critical (Tc) and the lethal (Tp) temperature of PS2 increased by at least 1 K. Thermotolerance of the leaf tissue (LT50) increased significantly by +0.6 K. The effects of slight water stress on thermotolerance of PS2 were species specific. High temperature thresholds for photoinhibition were significantly different between species and increased by 9 K from the species in the coldest microhabitat to the species in the warmest. Experimental heating of L. procumbens canopies by +3 K caused a significant (p>0.01) upward shift of the high temperature threshold for photoinhibition by +3 K. Each species appeared to be very well adapted to the thermal conditions of its microhabitat as under the most frequently experienced daytime leaf temperatures no photoinhibition occurred. The observed fine scale thermal adjustment of PS2 in response to increased leaf temperatures shows the potential to optimise photosynthesis under varying environmental conditions as long as the upper thermal limits are not exceeded. and V. Braun, O. Buchner, G. Neuner.
The common bean (Phaseolus vulgaris L.) is sensitive to high temperature, while an ecologically contrasting species (Phaseolus acutifolius A. Gray) is cultivated successfully in hot environments. In this study, the two bean species were respectively acclimated to a control temperature of 25 °C and a moderately elevated temperature of 35 °C in order to compare the thermotolerance capabilities of their photosynthetic light reactions. Growth at 35 °C appeared to have no obvious adverse effect on the photosynthetic activities of the two beans, but changed their thermotolerance. After a short period of heat shock (40 °C for up to 4 h), the photosynthetic activities of 25 °C-grown P. vulgaris declined more severely than those of P. acutifolius grown at 25 °C, implying that the basal thermotolerance of P. vulgaris is inferior to that of P. acutifolius. But after acclimating to 35 °C, the thermotolerances of the two species were both greatly enhanced to about the same level, clearly demonstrating the induction of acquired thermotolerance in their chloroplasts, and P. vulgaris could be as good as P. acutifolius. Temperature acclimation also changed plants' resistance to photoinhibition in a manner similar to those toward heat stress. In addition, acquisition of tolerance to heat and strong irradiance would reduce the dependency of the two beans on xanthophyll pigments to dissipate heat, and also seemed irrelevant to the agents with antioxidant activities such as SOD. and C. M. Tsai, B. D. Hsu.
The resistance to insulin (insulin resistance, IR) is a common feature and a possible link between such frequent disorders as non-insulin dependent diabetes mellitus (NIDDM), hypertension and obesity. Pharmacological amelioration of IR and understanding its pathophysiology are therefore essential for successful management of these disorders. In this review, we will discuss the mechanisms of action of thiazolidinediones (TDs), a new family of insulin-sensitizing agents. Experimental studies of various models of IR and an increasing number of clinical studies have shown that TDs normalize a wide range of metabolic abnormalities associated with IR. By improving insulin sensitivity in skeletal muscles, the adipose tissue and hepatocytes, TDs reduce fasting hyperglycaemia and insulinaemia. Furthermore, TDs markedly influence lipid metabolism - they decrease plasma triglyceride, free fatty acid and LDL-cholesterol levels, and increase plasma HDL-cholesterol concentrations. Although TDs do not stimulate insulin secretion, they improve the secretory response of beta cells to insulin secretagogues. TDs act at various levels of glucose and lipid metabolism — ameliorate some defects in the signalling cascade distal to the insulin receptor and improve glucose uptake in insulin-resistant tissues via increased expression of glucose transporters GLUT1 and GLUT4. TDs also activate glycolysis in hepatocytes, oppose intracellular actions of cyclic AMP, and increase intracellular magnesium levels. TDs bind to peroxisome proliferator activating receptors y (PPARy), members of the steroid/thyroid hormone nuclear receptor superfamily of transcription factors involved in adipocyte differentiation and glucose and lipid homeostasis. Activation of PPARy results in the expression of adipocyte-specific genes and differentiation of various cell types in mature adipocytes capable of active glucose uptake and energy storage in the form of lipids. Furthermore, TDs inhibit the pathophysiological effects exerted-fey tumour-necrosis factor (TNFa), a cytokine involved in the pathogenesis of IR. These effects are most likely also mediated by stimulation of PPARy. In mature adipocytes, PPARy stimulation inhibits stearoyl-CoA desaturase 1 (SCD1) enzyme activity resulting in a change of cell membrane fatty acid composition. Apart from their metabolic actions, TDs modulate cardiovascular function and morphology independently of the insulin-sensitizing effects. TDs decrease blood pressure in various models of hypertension as well as in hypertensive insulin-resistant patients, and inhibit proliferation, hypertrophy and migration of vascular smooth muscle cells (VSMC) induced by growth factors. These processes are considered to be crucial in the development of vascular remodelling, atherosclerosis and diabetic organ complications. TDs induce vasodilation by blockade of Ca2+ mobilisation from intracellular stores and by inhibition of extracellular calcium uptake via L-channels. Furthermore, TDs interfere with pressor systems (catecholamines, renin-angiotensin system) and enhance endothelium-dependent vasodilation. A key role of TDs effects in vascular remodelling is played by inhibition of the mitogen-activated protein (MAP) kinase pathway. This signalling pathway is important for VSMC growth and migration in response to stimulation with tyrosine-kinase dependent growth factors. In addition to the vasoprotective mechanisms mentioned above, troglitazone, the latest representative of this pharmacological group, possesses antioxidant actions comparable to vitamin E. In summary, TDs have the unique ability to attack mechanisms responsible for metabolic alterations as well as for vascular abnormalities characteristic for IR. Therefore, TDs represent a powerful research tool in attempts to find a common denominator underlying the pathophysiology of the metabolic syndrome X. A recently reported link between MAP kinase signalling pathway and PPARy transcriptional activity suggests that this research direction is promising.
The article presents a liquid film instability model designed using results of the set of CFD simulations. The governing equations of the model are derived using a linear equation of motion. The stability analysis is carried out by imposing a liquid surface disturbance which growth rate is investigated in dependence on the geometrical and physical configuration. The gas effect parameters, which are decisive variables in the model, are derived using results of the set of CFD simulations of turbulent flow in channel with wavy surface. The agreement between predicted and measured critical gas velocities and wavelengths in dependence on the liquid film thickness is very good. and Obsahuje seznam literatury
Daniconema anguillae Moravec et Koie, 1987 larvae measuring 1.64-1.76 mm were occasionally found in considerable numbers in the fins and subcutaneous connective tissue of approximately 50% of eel Anguilla anguilla (L.) sampled from Lake Balaton, Hungary. The larvae were noted for their slender body, very long tail with a rounded tip, a densely transversely striated cuticle, and the presence of boring tooth and large kidney-shaped amphids on the cephalic end. The larvae could easily be recovered from the above mentioned organs by placing them into isotonic saline solution. No disease signs or pathological changes attributable to the larval infection could be observed. The only histological indication of host reaction was the appearance of macrophages adhering to the body surface of larvae and of cells with spherical nucleus in areas around the larvae. A possible life cycle pattern of I), anguillae is discussed.