Fixation Characteristics Research Articles

The effects of different fixations on the distribution and numbers of mast cells in patients with nasal polyps.

Mast cells in rats have been categorized into mucosal and connective tissue mast cells by properties which include their fixation characteristics and their distribution in tissues. There are a number of factors which make this classification unsatisfactory including the variability of fixation, intensity of background staining and the application of animal studies to man. Seasonal allergic reactions in the nose of man occur both in the surface metachromatic cells and in those within the epithelium; the latter are presumed to be mucosal mast cells. The aim of this study was to look at the distribution and the fixation characteristics of mast cells in inferior turbinates and nasal polyps. Both techniques show that cells are more abundant in the submucosa and the fact that Carnoy's fixative shows them better and this may be due to the lack of intensity in the background staining. There is no evidence that mast cells are more frequent in the epithelium. These findings would suggest the nasal polyps are not an allergic disease.

DARK CARBON FIXATION STUDIES ON THE INTERTIDAL MACROALGA ASCOPHYLLUM NODOSUM (PHAEOPHYTA) 1

ABSTRACT The characteristics of dark carbon fixation by Ascophyllum nodosum were investigated. In longitudinal profile the maximum rates of dark and light dependent fixation are found at the apex. The use of Michaelis‐Menten kinetics did not suitably describe the relationship between the uptake rate in the dark and the total inorganic carbon concentration. Dark fixation was saturated at a total inorganic carbon concentration [TIC] of 2.5 mM. The use of the Hill‐Whittingham equation to describe the uptake curve indicates that the process is diffusion limited. Comparisons of dark fixation at high (8.0) and low (5.2) pH suggest that bicarbonate ions are used as a source of inorganic carbon. The transfer of 14C, fixed in the dark, from the ethanol soluble to the insoluble fraction was relatively slow irrespective of the light treatment during the chase period. Ascophyllum nodosum displays a small diel fluctuation in the pH of aqueous extracts and titratable acidity similar to that displayed by CAM plants. The significance of dark fixation to the overall carbon budget is discussed.

A Modified Technique for the Fixation of Pathologic Fractures in the Lower Femur

Intramedullary nail fixation augmented by the pressure injection of methylmethacrylate was investigated by use of bovine femora. In this technique, the nail is first placed in its final desired position; cement is then injected with a conical-tipped syringe through a distal drill hole into the medullary canal around the nail. This method was compared with the conventional technique of first placing the cement into the medullary canal and then driving the nail into position. Calf femora were used to compare the cement pressures generated, the shear resistance at the bone/cement interface, and the contour of the endosteal cement surface produced by the two cementing techniques. Significantly higher bone/cement interface pressures were generated by the injection of cement. Shear resistance at the bone/cement interface, investigated by push-out tests, revealed no significant difference between the two techniques. Dissolution of the specimens in nitric acid produced a methylmethacrylate cast of the endosteal surface, thus revealing the pattern of cement penetration into endosteal bone. The cement surfaces made by the injection of cement revealed characteristics of superior fixation and penetration compared to those made by the conventional method. The injection of cement for pathologic long-bone fractures is safer than the conventional method, is less susceptible to intraoperative complications, and offers satisfactory fixation.

Characteristics of N2 fixation in Mo-limited batch and continuous cultures of Azotobacter vinelandii.

Steady-state chemostat cultures of Azotobacter vinelandii were established in a simple defined medium that had been chemically purified to minimize Mo and that contained no utilizable combined N source. Growth was dependent on N2 fixation, the limiting nutrient being the Mo contaminating the system. The Mo content of the organisms was at least 100-fold lower than that of Mo-sufficient cultures, and they lacked the characteristic g = 3.7 e.p.r. feature of the MoFe-protein of nitrogenase. A characteristic of nitrogenase activity in vivo in Mo-limited populations was a disproportionately low activity for acetylene reduction, which was 0.3 to 0.1 of that expected from the rate of N2 reduction. Acetylene was also a poor substrate in comparison with protons as a substrate for nitrogenase, and did not markedly inhibit H2 evolution, in contrast with Mo-sufficient populations. In batch cultures in similar medium or 'spent' chemostat medium inoculated with Mo-limited organisms, the addition of Mo elicited a biphasic increased growth response at concentrations as low as 2.5 nM, provided that sufficient Fe was supplied. In this system V did not substitute for Mo, and Mo-deficient cultures ceased growth at a 25-fold lower population density compared with cultures supplemented with Mo. Nitrogenase component proteins could not be unequivocally detected by visual inspection of fractionated crude extracts of Mo-limited organisms. 35SO42-pulse-labelling studies also showed that the rate of synthesis of the MoFe-protein component of nitrogenase was too low to be quantified. However, the Fe-protein of nitrogenase was apparently synthesized at high rates. The discussion includes an evaluation of the possibility that A. vinelandii possesses an Mo-independent N2-fixation system.

An analysis of photosynthetic response and adaptation to temperature in higher plants: temperature acclimation in the desert evergreen Nerium oleander L*

Abstract. Factors underlying the process of photosynthetic acclimation to temperature were investigated for the shrub Nerium oleander L. Ramets of a single clone were grown under day/night temperature regimes of 20°C/15°C or 45°C/32°C. Plants grown at the lower temperature regime possessed rates of photosynthesis twice that of the high‐temperature grown plants when CO2 fixation was measured at 20°C. In contrast, the plants grown at the high‐temperature regime had twice the rate of CO2 fixation of the 20°C/l 5°C‐grown plants at a measurement temperature of 45° C. It was determined that the ability to acclimate to changes in temperature regime was present in fully mature leaves. A reciprocal transfer of plants between the two growth regimes resulted in the appearance of the CO2 fixation characteristics appropriate to the new growth temperature after 12–14d. The response of CO2 fixation to light, temperature, and CO2 partial pressure and the temperature responses of soluble and membrane‐bound photosynthetic enzyme systems were analysed to determine which components might be responsible for the superior photosynthetic performance of the 20°C/I5°C‐grown plants at 20°C, and the enhanced high‐temperature stability of the 45°C/32°C plants. The measured photosynthetic capacity of the 20°C/15°C plants could not be attributed to gross morphological, stomatal, or other physical changes, or to a general increase in the concentration of components of the photosynthetic process. Only a single enzyme, Fru‐P2 phosphatase, was affected to an extent similar to that of photosynthesis. The enhanced thermal stability of the 45°C/32°C plants may be attributed primarily to an enhanced stability of the chloroplast membrane‐bound enzymatic activities and the stability of the photosynthetic carbon metabolism enzymes which require lighl for activation.

Clay mineralogical and ammonium fixation characteristics of some tropical upland rice soils

Abstract In view of the agronomic and economic significance of NH4 fixation in soils, an attempt has been made to relate this to the most reactive mineral constituents of soils ‐ the clay minerals, under the temperature‐moisture regimes normal to tropical upland rice soils. Laboratory fixation study was done with NH4, concentrations similar to those common in soils upon N fertilization, and under alternate wetting and drying at ambient temperatures rather than at 100°C as in many published studies. Results of the investigation show that soil clays with dominant vermiculite and montmorillonite fix the greatest proportion of applied NH4 (94 and 91%), followed by beidellite (72%) and x‐ray amorphous (45–64%) clays. Fixation is negligible (10%) in the clay with mineral suite consisting of hydrous mica, halloysite, and chlorite. Crystallinity of minerals seems to influence NH4 fixation appreciably.

Evaluation of Phosphorus Fixation Capacity of Tropical Savannah Soils of Western Nigeria

AbstractIt is generally believed that tropical soils fix most Phosphorus (P) applied as fertilizers into forms not available to plants. To study fixation characteristics of savannah soils of western Nigeria, 22 surface soil samples varying in cropping histories, physical and chemical properties, and derived from igneous and metamorphic rocks were evaluated for capacities to fix soluble‐P with time.The fractional recovery (FR) which is the proportion of added P extracted by Bray's P1 (0.03N NH4F + 0.025N HCl) decreased with time following a pattern of rapid decline during the first few days of incubation and a slower decline thereafter. The decrease suggests an exponential relationship, and fits into the equationFR = ‐K ln t + C.The equations were used in calculating probable residual values of applied‐P at times within or outside the range of the experimental period.The high FR and residual values indicate that these soils fix little P in contrast to earlier‐held views about the P‐fixation capacity of tropical soils. The FR was significantly correlated with organic matter, clay, citrate‐dithionite‐extractable oxides of Fe and Al while there was no correlation with soil pH.

Some characteristics of symbiotic nitrogen fixation, yield, protein and oil accumulation in irrigated peanuts (Arachis hypogaea L.)

The potential of peanuts for symbiotic nitrogen fixation is considerable and under optimal edaphic and climatic conditions it reached 222 kg N2/ha, which was 58% of the nitrogen accumulated in the plants. The effect of the Rhizobium inoculation on crude protein accumulation in the yield (kg/ha) was 3–4 times greater than its effect on the yield of pods and hay. There was an inverse relationship between the protein and oil content in the kernels.

C4 characteristics of photosynthesis in the C3 alga Hydrodictyon africanum

Abstract Results obtained with Hydrodictyon africanum, and data from the literature, show that most green algae of the chlorophyte type (e.g. Chlorella, Chlamydomonas, Hydrodictyon) differ in their photosynthetic C fixation characteristics from most green algae of the charophyte type (e.g. Spirogyra, Chara) and from C3 higher plants. The chlorophyte algae fix inorganic carbon by the photosynthetic carbon reduction cycle pathway, but have a low CO2 compensation point in 250 μM O2, a low inhibition of CO2 fixation from 10 μM CO2/250 μM O2 when compared with 10 μM CO2/zero O2, and a low half‐saturation constant for CO2. These three characteristics are different from those of charophytes and C3 higher plants, and resemble those of C4 higher plants. It is suggested that these characteristics of chlorophyte algae are the result of a ‘CO2 concentrating mechanism’ which increases the CO2/O2 ratio at the site of ribulose bisphosphate carboxylase‐oxygenase action in a similar way to that achieved by the C4?C3 acid cycle in C4 plants. In the chlorophyte algae, however, CO2 concentration probably involves active HCO3− transport at the inner membrane of the chloroplast envelope. Active HCO3− transport can occur at the plasmalemma of charophyte algae and submerged aquatic higher plants as well as chlorophyte algae, so it is unlikely to explain the differences between the two groups of aquatic green plants. Differences in the properties of ribulose bisphosphate carboxylase‐oxygenase, and differences in CO2 production in the light, also seem inadequate to account for the different photosynthetic characteristics. The chlorophyte type of ‘C02 concentrating mechanism’ appears to be common in other classes of eukaryotic algae, and in cyanophytes. Some of the ‘advanced’ members of these eukaryotic algal classes (including the chlorophytes) may lack the mechanism, while some ‘primitive’ charophytes may retain the mechanism which their ancestors presumably possessed.

Interdependence of Nitrogen Nutrition and Photosynthesis in Pisum sativum L

Physiological responses to infection by strains of Rhizobium leguminosarum which differed in their capacity to reduce N(2) were determined in 26-day-old pea plants (Pisum sativum L. cv. Alaska) grown under uniform environmental conditions in the absence of combined N. The highest N(2) reduction rates, calculated from H(2) evolution and C(2)H(2)-dependent C(2)H(4) production measurements, were approximately 6-fold greater than the lowest. Higher N(2) fixation rates were associated with greater CO(2) exchange rates (R(2) = 0.92) and carboxylation efficiency (R(2) = 0.99). Increases in the apparent relative efficiency of N(2) fixation [1-(H(2) evolved in air/C(2)H(2) reduced)] (acteroid efficiency) were associated with increases in whole-plant N(2) fixation efficiency (N(2)/CO(2) reduction ratio) (R(2) = 0.95). Whole-plant dry weight and total N content were related by regression analysis (R(2) = 0.98); both parameters were enhanced by increased N(2) fixation in a manner analogous to previously reported increases caused by greater external applications of NH(4) (+). These data reveal that photosynthetic parameters in genetically uniform host plants grown under identical environmental conditions are affected by N(2) fixation characteristics of the rhizobial symbiont. The measured efficiencies of micro- and macrosymbiont are directly related under uniform environments.

THE CARBON FIXATION CHARACTERISTICS OF ISOLATED CODIUM FRAGILE CHLOROPLASTS. CHLOROPLAST INTACTNESS, THE EFFECT OF PHOTOSYNTHETIC CARBON REDUCTION CYCLE INTERMEDIATES AND THE REGULATION OF RuBP+ CARBOXYLASE IN VITRO

SUMMARYChloroplasts of the siphonaceous marine alga Codium fragile exhibit different carbon fixation characteristics in vitro from those of higher plants. A simple extraction medium, 0.8 M osmoticum and a saturating light intensity of 25 W.m−2 produced maximum rates of 40–60 μmoles CO2 fixed mg. chlorophyll−1 h−1 at 20°C, depending on the age and condition of the parent tissue. No marked lag phase was apparent and fixation proceeded at a linear rate for up to 60 min.Incubation with 10 mM PGA enhanced the fixation rate, as did 10 mM SBP, 10 mM FBP and 5 mM R5P to a lesser extent, whereas 6 PGlu, S7P, F6P, Ru5P and PEP produced no measureable effect. This lack of marked response to the addition of exogenous photosynthetic intermediates is correlated to a lack of induction by these chloroplasts.Using the retention of the soluble stromal enzyme RuBP carboxylase as a criterion of intactness, freshly isolated C. fragile chloroplasts were approximately 80% intact, and were still 40% intact after 96 h storage in the dark on ice.RuBP carboxylase was shown to resemble the higher plant carboxylase, existing in either an active or inactive form depending on the prevailing levels of RuBP and Mg2+, and to be metabolically regulated by PGA, 6PGlu, SBP, FBP and Pi. Maximum rates obtained with a chloroplast extract were 155 jumoles CO2 fixed mg chlorophyll−1 h−1, at 20°C.

Otosclerosis in Japanese

The incidence of otosclerosis in Japanese is low and only a few authors have reported temporal bone findings in otosclerosis.In our experience, six surgically acquired specimens from ears with typical audiometric characteristics of stapes fixation revealed foci which belonged to a classification of a true otosclerosis.The specimens showed all stages of otosclerotic maturation:i) osteoclastic destruction and osteoblastic activities around the newly forming bone.ii) osteoid blue bone with osteoblasts, forming the “blue mantle”.iii) acidphilic remodeling bone with osteoblasts.iv) highly mineralized acidphilic bones with a mosaic-like appearance.In most of stapes fixation in tissues from Japanese patients, the same otosclerosis as is seen in Caucasians was evident.

Guard cell malic acid metabolism during stomatal movements

THE mechanism by which stomata open and close has long been a puzzle, but only now are we beginning to make major advances in our understanding of their metabolism. It has been concluded that guard cells can fix CO2 and incorporate it into starch1–3. It has been shown that the bulk of, if not all, the CO2 fixed by guard cells is converted to oxaloacetic acid (OAA) by phosphoenolpyruvate carboxylase and the OAA, in turn, is reduced to malic acid3,4. Some amination of OAA producing aspartate has also been detected4. Although there is indirect evidence suggesting that aspartate and/or malate can provide carbon for starch synthesis in the guard cells4 direct evidence for this is lacking. We have investigated some characteristics of guard cell CO2 fixation which directly results in organic acid formation and we also have direct evidence that malic acid is a precursor of starch formation.

Physiology and chemical composition of nitrogen-fixing phytoplankton in the central North Pacific Ocean

The magnitude and physiological characteristics of biological nitrogen fixation have been studied in the oligotrophic waters of the North pacific gyre. The filamentous blue-green algae Trichodesmium spp. and Richelia intracellularis were the important nitrogen-fixing phytoplankton. Most of the nitrogen fixation occurs in the upper 40 m of the water column, with detectable fixation as deep as 90 m, which corresponds to about the 1 % light depth. There was no evidence of photoinhibition of nitrogen fixation, although CO2 reduction was depressed slightly at the highest light levels. The rate of nitrogen fixation in the water column varied throughout the day, being highest in mid-morning and in late afternoon. Relatively high fixation rates were also found during periods of darkness. Elevated oxygen concentrations had a marked inhibitory effect on rates of nitrogen fixation, a pO2 of 0.4 atm causing a 75% inhibition. Data from studies of nitrogen fixation and assimilation rates of 15N-labelled nitrate, ammonium, and urea indicate that nitrogen fixation furnished about 3% of the total daily fixed nitrogen requirement for phytoplankton growth. Studies with isolated colonies of Trichodesmium spp. indicated that 100% of their nitrogen requirement was met by nitrogen fixation. Chemical composition of the Trichodesmium colonies showed that the C:N ratio was 4.1 and that their phosphorus content relative to carbon or nitrogen was much lower than that of the total particulate material in the water column. Elevated ratios of carbon: adenosine triphosphate (ATP) also suggest that phosphorus deficiency may be limiting the growth of Trichodesmium. The magnitude of nitrogen fixation in the gyre is seasonally dependent, with high rates in late summer and autumn. At these times the water column is stratified, with phosphate and nitrate barely detectable in the upper 100 m. Our data suggest that during these months of stratification, biological fixation of nitrogen amounts to about 33 μg-at N/m2/day.

Proximal tubule tendrils: Fact or artefact

Tendrils have been reported to radiate from luminal surfaces of proximal tubules in rat kidneys by Andrews and Porter ('74) using scanning microscopy, but they were not seen by Bulger et al. ('74). In this study, the perfusion procedure of Andrews and Porter was re-investigated. Tendrils were found only in regions which had characteristics of poor fixation. They were especially prominent if the perfusion pressure was purposely allowed to fall and subsequently increased to re-expand the tubules. The tendrils could then be seen in all portions of the proximal convoluted tubule and not exclusively in the initial portion as previously reported.

Carbon dioxide assimilation in some aerial plant organs and tissues

CO2 fixation characteristics of a number of mature (but not senescing) tissues and organs (the outer layers of green pod and the seed testa of Vicia faba L.; the outer layers of green pod and seeds of Trigonella foenum-graecum L.; the outer layers of the green fruit of Lycopersicon esculentum Mill.) were studied and compared with their respective C3 leaf characteristics. On a chlorophyll basis phosphoenolpyruvate carboxylase, malic enzyme (NADP) and malate dehydrogenase (NAD and NADP) acitivites were much higher in the non-leaf tissues (except for V. faba seed testa) than the leaf tissues. Generally, on a protein basis the differences were less significant. All tissues possessed ribulose-1.5-diphosphate carboxylase activity though there was great variation in activities both on a protein and chlorophyll basis. Protein: chlorophyll ratios varied greatly from tissue to tissue being lowest in the leaf tissue (11.5-14.0) and highest in V. faba seed testa (805.5). Chlorophyll a:b ratios were all between 2 and 3. (14)CO2 uptake in the dark by L. esculentum fruit slices was about 1/3 that in the light and the major, initially labelled product was malate both in the light and dark. Neither typical C4-photosynthesis or crassulacean acid metabolism were exhibited by the non-leaf tissues and it was considered that the increased levels of certain enzyme activities were present to refix and recycle respired CO2.

Load Testing of Geometric and Polycentric Total Knee Replacements

Static loading of implanted geometric and polycentric knee replacements was conducted in order to define fixation characteristics and load capabilities of the prostheses and the bone prostheses interface. Failures occurred in some specimens at load levels normally encountered across the knee joint during ambulation. Disruption of the tibial bone-cement interface and crushing of the tibial plateau were the modes of failure. There was no failure on the femoral side of the joint. The major determinants of stress failure suggested by this study were: (1) the tibial bone strength, (2) the design of the geometric and polycentric tibial component, and (3) method of component implantation.

Simple forms and fluctuations of the line of sight: Implications for motor theories of form processing

A contact lens optical Jever was used to measure two-dimensional fixation characteristics when experienced Ss fixated at various positions within simple forms small enough to fall entirely on the foveal floor (<80 min). Fixation stability and the average direction of the line of sight were not markedly or systematically affected by the shape of the fixation stimulus. Similar results were obtained when all saccades were suppressed and the line of sight maintained exclusively by means of slow control. These results cast doubt on motor theories of form perception.

Characteristics of Complement Fixation by Aggregated IgE

Abstract Aggregated IgE fixed late components of complement (C), i.e., C3–C9, through an alternate pathway, bypassing C1, 4, and 2 whereas monomeric IgE did not. The aggregate, however, did not fix purified C3, suggesting that C3 activator system is involved in the reaction. On a weight basis, aggregated Fc had higher C-fixing activity than aggregated IgE, and aggregated F(ab′)2 was less active. The results indicated that structures essential for C fixation are present in the Fc portion of IgE molecules. A mild reduction and alkylation of IgE, which degraded structures involved in passive sensitization of monkey skin, did not affect the C-fixing properties of the protein.

Nonphotosynthetic Retardation of Chloroplast Senescence by Light

Excised apical portions of green wheat leaf sections were treated with aminotriazole to prevent formation of new chloroplasts. Illumination retarded the decline in chlorophyll content per leaf section, the disintegration of chloroplast ultrastructure, and the loss of capacity for photosynthetic carbon fixation. We interpret these 3 effects of illumination as facets of a single light effect in retarding chloroplast senescence. This light effect in retarding chloroplast senescence has features differing from characteristics of photosynthetic carbon fixation. For example, A) application of the photosynthetic inhibitor 3-(3,4-dichlorophenyl)-1, 1-dimethylurea did not decrease, and may have even slightly increased, the effectiveness of light; B) although the action spectrum contains peaks in the blue and red regions, it differs from the action spectrum for photosynthetic CO(2) assimilation in wheat; C) in nonphotosynthesizing tissue, application of sugars did not retard chloroplast senescence; D) light saturation was achieved by only a few hundred microwatts/cm(2). Considered together with the well-known light requirement for chloroplast formation, our results indicate that light has a dual, photomorphogenetic control in maintaining the green status of the plant by also exerting a second effect: retarding of senescence of chloroplasts already present.