Interactive effects of nutrient and mechanical stresses on plant morphology

BACKGROUND AND AIMS: Plant species frequently encounter multiple stresses under natural conditions, and the way they cope with these stresses is a major determinant of their ecological breadth. The way mechanical (e.g. wind, current) and resource stresses act simultaneously on plant morphological traits has been poorly addressed, even if both stresses often interact. This paper aims to assess whether hydraulic stress affects plant morphology in the same way at different nutrient levels. METHODS: An examination was made of morphological variations of an aquatic plant species growing under four hydraulic stress (flow velocity) gradients located in four habitats distributed along a nutrient gradient. Morphological traits covering plant size, dry mass allocation, organ water content and foliage architecture were measured. KEY RESULTS: Significant interactive effects of flow velocity and nutrient level were observed for all morphological traits. In particular, increased flow velocity resulted in size reductions under low nutrient conditions, suggesting an adaptive response to flow stress (escape strategy). On the other hand, moderate increases in flow velocity resulted in increased size under high nutrient conditions, possibly related to an inevitable growth response to a higher nutrient supply induced by water renewal at the plant surface. For some traits (e.g. dry mass allocation), a consistent sense of variation as a result of increasing flow velocity was observed, but the amount of variation was either reduced or amplified under nutrient-rich compared with nutrient-poor conditions, depending on the traits considered. CONCLUSIONS: These results suggest that, for a given species, a stress factor may result, in contrasting patterns and hence strategies, depending on a second stress factor. Such results emphasize the relevance of studies on plant responses to multiple stresses for understanding the actual ecological breadth of species.     

Effect of carbohydrate components of ristomycin A on platelet aggregation in human plasma

In the process of the investigation, conditions for specific removal of arabinose in tetrasaccharide of ristomycin A, a glycopeptide antibiotic as well as conditions for simultaneous removal of arabinose and mannose-2 bound to actinoidinic acid were determined. The role of arabinose in manifestation of the ristomycin A ability to induce platelet aggregation was shown to be important. Mannose-2 also had the same ability while its level was somewhat lower.     

Effect of couple stresses on the unsteady convective diffusion in fluid flow through a channel

A generalized dispersion model is used to obtain exact solution for unsteady convective diffusion in the presence of couple stresses. The effect of the couple stress parameter 'a' on the most dominant dispersion coefficient is clearly depicted. The dimensionless mean concentration distribution is obtained as a function of dimensionless axial distance, time and 'a'. The results for 'pure convection' are also reported. It is shown that the effect of couple stress is predominant only for small values of 'a' and when a----infinity the flow characteristics tend to their equivalents in Newtonian theory. The results of Taylor's dispersion model are recovered as a particular case in the limit tau----infinity.     

LDL受体介导的血浆低密度脂蛋白胆固醇的内吞

胆固醇是动物细胞细胞膜的重要组成成分,其做为细胞和环境之间的屏障调节细胞膜的流动性。胆固醇是体内所有的类固醇激素和胆酸合成的前体物质,参与体内代谢。同时胆固醇在神经系统的发育中也起着重要的作用。在血浆中胆固醇以低密度脂蛋白和高密度脂蛋白这两种胆固醇运载血脂蛋白的形式运输。动物细胞通过细胞表面的低密度脂蛋白受体(LDL receptor,LDLR)介导的内吞可以从血液中摄取富含胆固醇的低密度脂蛋白,当细胞表面的LDLR的功能缺陷时,可以导致高胆固醇血症,继而引起动脉粥样硬化、冠心病和中风等严重疾病。本文综述了LDL受体的概述及其通过内吞调节血液中低密度脂蛋白胆固醇水平的作用,并对LDL受体的调节进行了阐述。     

Effect of fish oil and coconut oil diet on the LDL receptor activity of rat liver plasma membranes

The influence of 4 weeks treatment with fish oil and coconut oil enriched diets on the chemical composition of rat liver plasma membranes and LDL and on the binding of LDL to liver membranes was investigated. Rats fed fish oil diet showed a total, LDL and HDL plasma cholesterol concentration lower than the values observed in rats fed coconut oil and to a lesser extent lower than those of rats fed standard laboratory diet. LDL of rats on fish oil diet had a relative percentage of cholesterol and phospholipid lower, while that of triacylglycerol was greater. Furthermore, fish oil feeding was associated with a greater concentration of n - 3 fatty acids and a lower arachidonic and linoleic acid content in LDL. Liver plasma membranes isolated from fish oil rats showed a higher percentage of n - 3 fatty acids, while only a trace amount of these fatty acids was found in control and coconut oil fed animals. In binding experiments performed with LDL and liver membranes from fish oil fed rats and control rats, binding affinity (Kd = 3.47 +/- 0.93 and 4.56 +/- 1.27, respectively) was significantly higher (P less than 0.05) as compared to that found using membranes and lipoprotein from coconut oil fed rats (Kd = 6.82 +/- 2.69). In cross-binding experiments performed with fish oil LDL and coconut oil liver plasma membranes or coconut oil LDL and fish oil liver plasma membranes, the LDL binding affinity was comparable and similar to that found in fish oil fed animals. No difference was found in the Bmax among all the groups of binding experiments. Our data seem to indicate that during fish oil diet the higher binding affinity of LDL to liver plasma membranes might be partly responsible of the hypocholesterolemic action of marine oil rich diet as compared to saturated diet. Furthermore, the modifications of binding affinity induced by changes of LDL and membrane source, suggest that lipoprotein and liver plasma membrane composition may be an important variable in binding studies.     

Effect of ultrafiltrates in plasma from patients with chronic uremia on platelet aggregation]

An effect of 20 ultrafiltrates from patients with chronic renal failure on ADP-, epinephrine-, and arachidonic acid-induced platelet aggregation. Ultrafiltrates were collected at the beginning and the end of dialysis. It was found that ultrafiltrates collected at the beginning of dialysis decrease ADP-induced platelet aggregation whereas ultrafiltrates collected at the and of dialysis exert reverse effect. No effect on epinephrine- and arachidonic acid-induced platelet aggregation was seen. Removal of substances inhibiting platelet aggregation produced by ADP hemodialysis may reveal increased platelet aggregation in patients with uremia.     

Collagenous constituents of amniotic fluid.

The amniotic fluid (AF) was fractionated by dialysis, gel filtration and SDS/PAGE, and submitted to the assay of collagenous constituents. The collagenous character of peptides and proteins of amniotic fluid was confirmed by hydroxyproline (Hyp) assay and treatment with bacterial collagenase followed by electrophoresis and gel filtration of the digestion products. It was found that AF contains collagen degradation products but the classical method of Hyp determination described by Woessner (Arch. Biochem. Biophys., 1961, 93, 440-447) gives overestimated values due to the interference with other AF components. Fractionation of AF on Sephadex G-100 column allowed to remove the interfering material and to estimate the actual Hyp content which equals to approx. 6.2 microg/ml. About 70% of Hyp was found in low molecular dialyzable products and the rest (about 30%) appears to be a constituent of nondialyzable collagenous polypeptides of the molecular mass of about 7.9-26.3 kDa. It is suggested that such collagenous polypeptides may be the products of proteolytic conversion of collagen precursor (procollagen) into the monomeric form of this protein. No high molecular forms of collagen, corresponding to alpha-subunits, were found.     

Effect of chronic maternal hyperkalaemia on plasma, cerebrospinal fluid and brain interstitial fluid potassium in developing rats

Plasma hyperkalaemia was induced in pregnant and lactating rats using a high potassium diet. Fetuses of high-K-diet mothers showed no increase in the potassium concentration [( K+]) of plasma, cerebrospinal fluid (CSF) and brain interstitial fluid, presumably due to placental control. Neonates from high-K-diet rats did show an increase in plasma [K+] but this increase was very small and there was no increase in CSF or interstitial fluid [K+]. Maternal milk [K+] was not affected by plasma hyperkalaemia. Weanling rats fed the high-K diet directly showed marked plasma hyperkalaemia but no increase in CSF or interstitial fluid [K+]. Thus, prior to weaning, a relatively stable plasma [K+] is maintained by maternal influence reducing the need for direct brain fluid K+ regulation.     

New constituents and antiplatelet aggregation and anti-HIV principles of Artemisia capillaris

Five new constituents including a flavonoid, artemisidin A (1), and four coumarins, artemicapins A (2), B (3), C (4) and D (5), together with 70 known compounds (6-75), have been isolated and characterized from the aerial part of Artemisia capillaris. The structures of these compounds were determined from spectral analyses and/or chemical evidence. Among them, 15 compounds (3, 6, 10, 18. 30-32, 38-41, 44, 45, 51, and 55) showed antiplatelet aggregation activity and three compounds (10, 17, and 51) demonstrated significant activity against HIV replication in H9 lymphocytic cells.     

Studies on the inhibition of human thrombin: effects of plasma and plasma constituents

The effects of blood plasma and some plasma constituents on several types of thrombin inhibitors were quite varied. Two active esters were rapidly destroyed by serum albumin; one of these reacted initially with Lys-199, the residue that is also acylated by aspirin. Of two sulfonyl fluorides one was unaffected by albumin, and the other bound reversibly to albumin; this binding was greater with albumin acetylated at Tyr-411 near the binding site for medium-chain fatty acids. The effects of a chloromethyl ketone were inhibited, apparently reversibly, by albumin but were practically abolished by glutathione. Of two potent reversible inhibitors one was unaffected by plasma constituents, while the other was over 10-fold less potent in plasma than in fibrinogen. The effect of plasma could be partially explained by binding to albumin and lipoproteins.     

Cathepsin G activity lowers plasma LDL and reduces atherosclerosis

Cathepsin G (CatG), a serine protease present in mast cells and neutrophils, can produce angiotensin-II (Ang-II) and degrade elastin. Here we demonstrate increased CatG expression in smooth muscle cells (SMCs), endothelial cells (ECs), macrophages, and T cells from human atherosclerotic lesions. In low-density lipoprotein (LDL) receptor-deficient (Ldlr^–/–) mice, the absence of CatG reduces arterial wall elastin degradation and attenuates early atherosclerosis when mice consume a Western diet for 3 months. When mice consume this diet for 6 months, however, CatG deficiency exacerbates atherosclerosis in aortic arch without affecting lesion inflammatory cell content or extracellular matrix accumulation, but raises plasma total cholesterol and LDL levels without affecting high-density lipoprotein (HDL) or triglyceride levels. Patients with atherosclerosis also have significantly reduced plasma CatG levels that correlate inversely with total cholesterol (r = –0.535, P < 0.0001) and LDL cholesterol (r = –0.559, P < 0.0001), but not with HDL cholesterol (P = 0.901) or triglycerides (P = 0.186). Such inverse correlations with total cholesterol (r = –0.504, P < 0.0001) and LDL cholesterol (r = –0.502, P < 0.0001) remain significant after adjusting for lipid lowering treatments among this patient population. Human CatG degrades purified human LDL, but not HDL. This study suggests that CatG promotes early atherogenesis through its elastinolytic activity, but suppresses late progression of atherosclerosis by degrading LDL without affecting HDL or triglycerides.     

Common and rare gene variants affecting plasma LDL cholesterol

The plasma level of LDL cholesterol is clinically important and genetically complex. LDL cholesterol levels are in large part determined by the activity of LDL receptors (LDLR) in the liver. Autosomal dominant familial hypercholesterolaemia (FH) - with its high LDL cholesterol levels, xanthomas, and premature atherosclerosis - is caused by mutations in either the LDLR or in APOB - the protein in LDL recognised by the LDLR. A third, rare form - autosomal recessive hypercholesterolaemia - arises from mutations in the gene encoding an adaptor protein involved in the internalisation of the LDLR. A fourth variant of inherited hypercholesterolaemia was recently found to be associated with missense mutations in PCSK9, which encodes a serine protease that degrades LDLR. Whereas the gain-of-function mutations in PCSK9 are rare, a spectrum of more frequent loss-of-function mutations in PCSK9 associated with low LDL cholesterol levels has been identified in selected populations and could protect against coronary heart disease. Heterozygous familial hypobetalipoproteinaemia (FHBL) - with its low LDL cholesterol levels and resistance to atherosclerosis - is caused by mutations in APOB. In contrast to other inherited forms of severe hypocholesterolaemia such as abetalipoproteinaemia - caused by mutations in MTP - and homozygous FHBL, a deficiency of PCSK9 appears to be benign. Rare variants of NPC1L1, the gene encoding the putative intestinal cholesterol receptor, have shown more modest effects on plasma LDL cholesterol than PCSK9 variants, similar in magnitude to the effect of common APOE variants. Taken together, these findings indicate that heritable variation in plasma LDL cholesterol is conferred by sequence variation in various loci, with a small number of common and multiple rare gene variants contributing to the phenotype.     

Effect of diazinon, an organophosphate insecticide, on plasma lipid constituents in experimental animals

There has been increasing interest in studying the various effects of organophosphate insecticides in humans and experimental animals. Only a few data are available on the effect of the organophosphate insecticide, diazinon, on lipid metabolism. The aim of this study was to evaluate the effect of diazinon on plasma lipid constituents in mammalian animals. The plasma levels of total cholesterol (TC), high-density lipoprotein cholesterol (HDL-C), low-density lipoprotein cholesterol (LDL-C), triglycerides (TG), and phospholipids (PL) were measured in albino rats that were orally treated with a single dose of diazinon at a level of LD(50) or with repeated daily doses at the levels of 1/2, 1/8, and 1/32 LD(50) for 2, 8, and 32 days, respectively. After a 24 h post-treatment with a single LD(50) dose of diazinon, TC was not significantly changed, the HDL-C and PL levels were significantly decreased, but the LDL-C and TG levels were significantly increased. Separate daily oral administrations of diazinon at 1/2 LD(50), 1/8 LD(50), and 1/32 LD(50) doses resulted in a significant decrease in HDL-C and PL, with no significant change in TG. The LDL-C levels were significantly increased and TC showed no significant change with 1/2 LD(50) and 1/32 LD(50) doses of diazinon, whereas a significant decrease in the levels of TC, HDL-C, as well as LDL-C, was observed with the 1/8 LD(50) dose. These data suggest that diazinon may interfere with lipid metabolism in mammals.     

Effect of aging on mechanical stresses,deformations, and hemodynamics in human femoropopliteal artery due to limb flexion

Femoropopliteal artery (FPA) reconstructions are notorious for poor clinical outcomes. Mechanical and flow conditions that occur in the FPA with limb flexion are thought to play a significant role, but are poorly characterized. FPA deformations due to acute limb flexion were quantified using a human cadaver model and used to build a finite element model that simulated surrounding tissue forces associated with limb flexion-induced deformations. Strains and intramural principal mechanical stresses were determined for seven age groups. Computational fluid dynamics analysis was performed to assess hemodynamic variables. FPA shape, stresses, and hemodynamics significantly changed with age. Younger arteries assumed straighter positions in the flexed limb with less pronounced bends and more uniform stress distribution along the length of the artery. Even in the flexed limb posture, FPAs younger than 50 years of age experienced tension, while older FPAs experienced compression. Aging resulted in localization of principal mechanical stresses to the adductor hiatus and popliteal artery below the knee that are typically prone to developing vascular pathology. Maximum principal stresses in these areas increased threefold to fivefold with age with largest increase observed at the adductor hiatus. Atheroprotective wall shear stress reduced after 35 years of age, and atheroprone and oscillatory shear stresses increased after the age of 50. These data can help better understand FPA pathophysiology and can inform the design of targeted materials and devices for peripheral arterial disease treatments.