Regulation of principal cell pH by Na/H exchange in rabbit cortical collecting tubule

Summary Changes in intracellular pH (pH _i ) were measured using the pH indicator, BCECF, in principal cells from split opened cortical collecting tubules (CCTs) derived from rabbits maintained on a normal diet. This monolayer preparation has the advantage of allowing us to visualize the morphological differences in the two major cell types in this nephron segment under transmitted light. The visual identification of the cell types was verified using emission measurements taken from single principal and intercalated cells in the opened tubule which had been exposed to fluorescein isothiocyanate (FITC)-labeled peanut lectin. We confirmed the existence of an amiloride-sensitive Na/H exchange process activated during intracellular acidosis in principal cells. In addition, the exchanger was active under basal conditions and over a wide range of pH _i . Because the exchanger was active under basal conditions we tested the hypothesis that changes in intracellular Na (Na _i ) would alter pH _i in a predictable way. Maneuvers designed to alter Na _i were without significant effects within a 10-min time frame. Specifically, addition of 100 m ouabain to increase Na _i or exposure of the tubules to 10^–5 m amiloride to decrease luminal Na entry and reduce Na _i did not have an effect on pH _i . In some experiments we did observe however, after a 30-min exposure to ouabain, a small decrease in pH _i . These results suggest that Na/H exchange is a major regulator of pH _i in principal cells. However, regulation of Na transport by changes in pH _i in principal cells of rabbit CCT via the activity of a Na/H exchanger do not seem to contribute to the feedback control of Na transport.This work was supported by U.S. Public Health Service grants DK27847 to L.G. Palmer and DK11489 to E.E. Windhager.     

Variation in tissue element concentrations in Quercus ilex L. over a range of different soils

In order to study the variability in nutrient concentrations in four tissues of Q. ilex in relation to soil properties, we selected fifteen stands in both Quercus ilex forests and Q. ilex-Pinus halepensis mixed forests. These stands had developed on soils derived from eight different parent materials. Three soil groups were differentiated according to their chemical properties: calcareous soils, siliceous soils, and volcanic soils. Across sites, nutrient concentrations were generally less variable in current-year tissues than in older tissues. Nitrogen and potassium showed the lowest variability among sites, their concentrations in current-year leaves ranging from 1.17% to 1.39% for N and from 0.53% to 0.68% for K. There were few statistically significant correlations between tissue element concentrations, the most frequent being the antagonistic relationship between calcium and magnesium. Nitrogen concentration in current-year leaves was negatively correlated with soil chemical fertility (nitrogen, phosphorus and potassium). This may reflect a nutritional imbalance between nitrogen and other nutrients, some of which may be more limiting than nitrogen to Q. ilex growth in Catalonia forests. Negative correlations were also found between plant magnesium and soil calcium, and positive correlations between plant calcium and soil calcium.     

The influence of summer and winter stress and water relationships on the distribution of Quercus ilex L.

Several aspects of plant-water relationships and canopy behaviour have been studied over several years in two experimental areas of Quercus ilex L. forests in the northeastern Iberian Peninsula. Water requirements, water status limits necessary for a positive carbon budget and the functional canopy behaviour in the face of abiotic stress were evaluated, in order to determine which factors influence the geographical range of these forests.The results showed that holm oak has a conservative water use, a low cuticular transpiration, a high capacity for osmotic adjustement and xerophytic characteristics in leaf morphology and canopy arrangement. More than 440 mm of annual rainfall are required for these forests to persist. Summer drought and winter cold are thus important abiotic factors limiting the distribution of Quercus ilex. In both cases, drought stress is involved.     

亚洲高海拔锄足蟾的属间亲缘关系、分化及其与青藏高原形成的关系

本文在研究高海拔锄足蟾的属间分类及分布规律的基础上,对所属的齿蟾属Oreolalax、齿突蟾属Scutiger的齿突蟾亚属Scutiger,(Scutiger)和猫眼蟾亚属Scutiger(Aelurophryne)的成体外形和骨骼、蝌蚪的形态以及核型等24个性状进行综合分析,同时探讨了属间亲缘关系。结果表明:齿蟾属较原始,齿突蟾属较特化,它们可能起源于共同的祖先——原始齿蟾。在齿突蟾属中猫眼蟾亚属比齿突蟾亚属更为特化,后者与齿蟾属的亲缘关系相对较近。它们的分化与青藏高原的抬开有密切关系。     

Current-voltage curve of electrogenic Cl− pump predicts voltage-dependent Cl− efflux inAcetabularia

Summary The current-voltage relationship of carrier-mediated, passive and active ion transport systems with one charge-carrying pathway can exactly be described by a simple reaction kinetic model. This model consists of two carrier states (one inside, one outside) and two pairs (forwards and backwards) of rate constants: a voltage-dependent one, describing the transport of charge and a voltage-insensitive one, summarizing all the other (voltage-independent) reactions. For the electrogenic Cl^– pump inAcetabularia these four rate constants have been determined from electrical measurements of the current-voltage relationship of the pump (Gradmann, Hansen & Slayman, 1981;in: Electrogenic Ion Pumps, Academic Press, New York). The unidirectional Cl^– efflux through the pump can also be calculated by the availiable reaction kinetic parameters.³⁶Cl^– efflux experiments on singleAcetabularia cells with simultaneous electrical stimulation (action potentials) and recording, demonstrate the unidirectional Cl^– efflux to depend on the membrane potential. After subtraction of an efflux portion which bypasses the pump, agreement is found between the measured flux-voltage relationship and the theoretical one as obtained from the reaction kinetic model and its parameters from the electrical data.     

Nutritional requirements for conidial germination and hyphal growth of Beauveria bassiana

Nutritional requirements for germination and growth of the entomopathogenic fungus Beauveria bassiana are not complex. For germination to occur, a utilizable source of carbon must be present; however, a nitrogen source is needed for continued hyphal growth, otherwise lysis ensues. Compounds that can serve as utilizable carbon-energy sources for germination include glucose, N-acetylglucosamine, glucosamine, chitin, starch, lanolin, hydrocarbons in crude oil, and some longer-chain fatty acids. Both organic and inorganic sources of nitrogen are readily utilized for growth. Conidia undergo active metabolism soon after being placed in a suitable growth medium, indicating that conidia are released from their state of dormancy several hours before emergence of the germ tube can be observed. Because of the nutritional versatility of B. bassiana, this fungus should be able to survive and be infective in several types of natural environments.     

Effects of light, temperature and nitrogen treatments upon the fatty acid composition of galactolipids of young and older leaves from winter rape plants

40 aromatic and chlorocyclohexenic structural analogues of abscisic acid were synthesized stereospecifically, and inhibition of transpiration was investigated following two experimental procedures (cut barley leaves and water stressed cotton plants). Structure-activity relationships are discussed. – Two chlorosubstituted cyclohexenic compounds are the most active; their inhibition of transpiration can be compared to that of abscisic acid.     

Ethylene formation by germinating,Drechslera graminea — Infected barley (Hordeum sativum) grains: A simple test for fungicides

Grains of barley (Hordeum sativum L.); infected with the parasitic, systemic fungus Drechslera graminea, produce more ethylen than uninfected controls. Treatment of infected grains with mercury-free fungicides yields a differentiated suppression of the ethylene evolution 7 d after the beginning of germination. Suppression of visible symptoms (chlorotic stripes on leaves) appearing six to eight weeks after germination of infected, untreated seeds correlates with the decrease in ethylene formation after treatment with fungicides. The gaschromatographic ethylene determination thus allows for an early and reliable (significance higher than 99.9%) differentiation of fungicidal activities against the barley stripe disease.Abbreviations ACC I-aminocyclopropane-1-carbonic acid - CD critical difference     

Relative addition rate and external concentration; Driving variables used in plant nutrition research

Abstract An increasing literature accounting for various types of experiments indicates that far lower external nutrient concentrations are required by plants than is usually thought to be the case. It is concluded that the ion uptake capacity of the roots, as described by the carrier concept, is high compared to that required for maintenance of the internal concentration. Serious errors in experimental conclusions are associated with insufficient and constant nutrient addition rates. The main errors are caused by non-steady states of the plants both with regard to the internal nutrient concentrations and the relative growth rate. A dynamic concept has been proposed for direct use as the treatment variable within the range of sub-optimum nutrition. The nutritional factor is expressed as a flow, the relative nutrient addition rate in laboratory studies and the nutrient flux density in the field. The experimental use of the relative addition rate has led to steady-state nutrient status and relative growth rate and the interpretation of plant responses which differ fundamentally from accepted views. Thus, for instance, deficiency symptoms disappear, as in natural conditions, when the internal nitrogen concentration is stable, independent of level. The nutrition/growth relationships are very different from those observed when external concentration is varied. The regression line of relative growth rate on relative addition rate passes near to the origin at an angle close to 45 to the axes, which implies that the obtained relative growth rate approximates closely the treatment variable. A striking example of observed differences is the positive effect on nitrogen fixation exerted by high relative nitrogen addition rates compared to the well-known negative effect of increasing external nitrogen concentration. The application of fertilizer on the basis of the nutrient flux density concept provides the possibility of supplying fertilizers corresponding to the consumption potential of the vegetation and to the natural flux density resulting from mineralization in the soil. Nitrogen utilization is high under such conditions and the resulting feedback of nutrition on the mineralization rate suggests that there will be a long-term increase in fertility.     

Preferred conformations and flexibility of aminoacyl side chain of penicillins

Possible conformations of penicillin G; d and l isomers of ampicillin; α-amino-α-methyl-benzyl penicillins and 3- pyridyl methyl penicillin have been studied by an energy minimization procedure using empirical potential functions. The preferred conformations of these antibiotics have been correlated with their biological activity. The conformational requirement of the antibiotic to be active against Gram-positive and Gram-negative (β-lactamase-negative) bacterial strains seems to be the same. The reduced activity of penicillin G against Gram-negative bacteria has been attributed to its lower ability to permeate the outer membrane. The flexibility of the sidechains of these antibiotics is also shown to be important for the desired biological activity.