Prunus necrotic ringspot virus isolates in stone fruit germplasm accessions and cultivars in Israel

Prunus necrotic ringspot virus (PNRSV) was detected in almonds, plum and apricot germplasm accessions and local almond cultivars in Israel. PNRSV was widespread both in wild and cultivated almond trees and uncommon in wild apricots and plums. The possible variation among the PNRSV isolates was initially evaluated by restriction analysis of PCR products representing the CP gene with the endonuclease RsaI and followed by nucleotide sequence analysis of selected isolates. It was concluded that all 13 isolates belong to group PV96, the largest cluster of PNRSV isolates, described previously. Two PNRSV isolates, one from a plum accession and one from an almond cultivar, were found to be distinct members of group PV96 with unique nucleotide modifications not found in other documented isolates of this virus. However, no PNRSV isolate typical to a specific host and/or to the Middle East region could be identified. This study expands the body of data on variability of PNRSV isolates and highlights the importance of assessing the virus status of germplasm collections by applying reliable diagnostic and differentiating methods.     

Platelet activating factor (PAF) stimulates release of PGI2 from inflamed rabbit gallbladder cell cultures

This study examines the hypothesis that PAF stimulates release of PGI₂ from inflamed rabbit gallbladder explant cell cultures. New Zealand white rabbits underwent bile duct ligation for 72 h (72 h BDL), or sham operation, Sham and 72 h BDL gallbladder explants were placed in culture, and the cells grown to 75% confluence. The cells were exposed to increasing concentrations of PAF for 60 min. The media analyzed for eicosanoid release by EIA and the cells analyzed for cyclooxygenase and prostacyclin synthase content by immunoblot analysis. PAF increased release of 6-keto-PGF_1α from the 72 h BDL gallbladder cell cultures in a dose-related manner which was inhibited by indomethacin preincubation by 90%. The increased 72 h BDL cell release of 6-keto-PGF_1α was not associated with changes in the content of cyclooxygenase or prostacyclin synthase. PAF did not alter eicosanoid release from sham control cell cultures. These data suggest that PAF can only up-regulate endogenous 6-keto-PGF_1α release from the 72 h BDL cells that had been previously stimulated by inflammation. PAF may thus contribute to gallbladder distention and injury by chronic stimulation of inflamed gallbladder PGI₂ release.     

Epithelial cell volume modulation and regulation

Summary Epithelial cell volume is a sensitive indicator of the balance between solute entry into the cell and solute exit. Solute accumulation in the cell leads to cell swelling because the water permeability of the cell membranes is high. Similarly, solute depletion leads to cell shrinkage. The rate of volume change under a variety of experimental conditions may be utilized to study the rate and direction of solute transport by an epithelial cell. The pathways of water movement across an epithelium may also be deduced from the changes in cellular volume. A technique for the measurement of the volume of living epithelial cells is described, and a number of experiments are discussed in which cell volume determination provided significant new information about the dynamic behavior of epithelia. The mechanism of volume regulation of epithelial cells exposed to anisotonic bathing solution is discussed and shown to involve the transient stimulation of normally dormant ion exchangers in the cell membrane.     

Structure ofNecturus gallbladder epithelium during transport at low external osmolarities

Summary Gallbladders transport isotonically over a wide range of osmolarities. This ability has been assumed to depend on the geometry of the lateral intercellular spaces. We report that this geometry in theNecturus gallbladder varies extensively with the external osmolarity and dependsin vitro on the integrity of the subepithelial tissues. The structure of the living epithelium was studied by Nomarski light microscopy while ultrastructural effects were revealed by electron microscopy. The short-term effects (<60 min) of low external osmolarities were: 1) the cells became bell-shaped with an increased cell height measured centrally, 2) lateral intercellular spaces lost their convoluted character; and 3) numerous membrane-bound cavities appeared in the cells. Furthermore, long-term exposure to the low external osmolarities caused an uneven density of epithelial cells. With subepithelial tissues intact, blistering of the epithelium cell layer was evident. Qualitative electron-microscopic data indicate that the membrane of the cavities was recruited from the basolateral cell membrane. This agrees well with light-microscopic observation that the cavities were initiated as invaginations of this cell membrane.     

Cyclic AMP and intracellular ionic activities innecturus gallbladder

Summary Open-tip and liquid ion-exchanger microelectrodes were used to study the effects of cAMP (6mm, added to the serosal medium) on apical membrane potential (E _m ) and intracellular sodium, potassium, and chloride activities (a _Na ⁱ ,a _K ⁱ ,a _Cl ⁱ ) inNecturus gallbladder under open-circuit conditions. Transepithelial potential difference (E _Tr ) was also measured. In the presence of cAMP,a _Cl ⁱ fell from about 1.5 times its equilibrium value to a level that corresponded to electrochemical equilibrium across the apical and basolateral cell membranes. Under these conditionsa _Na ⁱ decreased anda _K ⁱ increased,E _m was unchanged andE _Tr increased from virtually zero to a small but significant serosal positive value. The cAMP-induced increase ina _K ⁱ was abolished when Cl^–-free incubation media were used. Addition of the Ca⁺⁺-ionophore A23187 (0.5 g/ml) to the serosal medium had no effect onE _m ,E _Tr , ora _Cl ⁱ . When A23187 was added to the mucosal medium,E _m and the basolateral membrane potential hyperpolarized by about 20 mV and an increase in the outwardly directed electrochemical driving force for Cl^– was observed. These results indicate that cAMP inhibits coupled transapical Na–Cl entry into epithelial cells ofNecturus gallbladder and suggest that this inhibition may not be mediated by an increase in intracellular Ca⁺⁺ concentration.     

The effect of electrical gradients on current fluctuations and impedance recorded fromNecturus gallbladder

Summary Transepithelial current fluctuations were recorded inNecturus gallbladder, clamped at negative as well as positive potentials up to 64 mV. With NaCl-Ringer's (+10mm TAP) on both sides a mucosa-negative potential enhanced the relaxation noise component, present at zero potential, and produced peaking in the power spectrum at potentials above –36mV. Concomitantly at these potentials an inductive as well as a capacitive low-frequency feature appeared in the impedance locus. Clamping at positive potentials of 18 mV suppressed the relaxation noise component. At potentials above 51mV the spectral values increased predominantly at low frequencies. In this case the power spectrum showed only a 1/f noise component. The experiments confirm the previous finding that a K⁺ efflux through fluctuating apical K⁺ channels exists under normal conditions. With serosal KCl-Ringer's the initial Lorentzian component was enhanced at negative but suppressed at positive potentials. The increase at negative potentials was less pronounced than in experiments with NaCl-Ringer's on both sides, indicating saturation of the fluctuating K⁺ current component. With mucosal KCl-Ringer's a negative potential depressed the initial relaxation noise component, whereas it was enhanced at +18 mV clamp potential. In the latter case an additional Lorentzian component became apparent at higher frequencies. At potentials of 36 mV and above the low-frequency Lorentzian disappeared whereas the corner frequency of the high-frequency component increased. The latter experiments demonstrate that the relaxation noise component inNecturus gallbladder consists of two superimposed Lorentzians. As the relaxation times of these two components behave differently under an electrical field, there may exist two different types of K⁺ channels. It is demonstrated that peaking in the plateau of power spectra can be explained by frequency-dependent attenuation effects, caused by a polarization impedance.     

中国主要五针松群落学特征及其生物量的研究

本文根据现有的文献资料,系统地分析了中国五针松的分布．群落学特征,按不同分布区、不同群落类型探讨了中国五针松的群落生物量和年净生产量及在群落的不同层次上的分布．比较分析了不同分布区五针松的年干物质累积速度（ＮＰ／Ｂ）．结果表明：１１５─１３５ａ生的阔叶红松林群落生物量在９７．０９─１２０．５１ｔ／ｈｍ￣２之间,年净生产量在８．６９８─１０．３４ｔ／ｈｍ￣２．ａ之间,年净生产量长白山山脉沙松、鹅耳枥红松林＞小兴安岭南坡枫桦、水曲柳红松林＞小兴安岭北坡云杉、冷杉红松林;３０─３６ａ生的华山松林群落生物量在７８．７５─９４．７３ｔ／ｈｍ￣２之间,年净生产量在４．９９３─５．５３７ｔ／ｈｍ￣２．ａ之间,年净生产量贵州山地常绿阔叶华山松林＞秦岭中山地阔叶华山松林＞甘肃小陇山针阔叶华山松林．ＮＰ／Ｂ值：长白山山脉的阔叶红松林＞小兴安岭山脉的阔叶红松林;秦岭中山地阔叶华山松林＞甘肃小陇山针阔华山松林＞贵州中山地常绿阔叶华山松林．     

Long-tailed macaques select mass of stone tools according to food type

Tool selection can affect the success of a tool-based feeding task, and thus tool-using animals should select appropriate tools when processing foods. We performed a field experiment on Piak Nam Yai Island in Laem Son National Park, Thailand, to test whether Burmese long-tailed macaques (Macaca fascicularis aurea) selected stone tools according to food type. We baited the island''s shores with stone sets (‘tool tests’) in an effort to attract macaques to use stones presented in a quasi-experimental design. Tool tests were placed at 344 locations for 126 days over a 2 year period, with each set containing four stones of different mass (categories: X, 40–60 g; S, 90–100 g; M, 150–200 g; and L, 400–1000 g). Tool tests were checked when we could access them. The number of times each tool test was checked varied (1–32), for a total of 1950 checks. We also studied 375 non-experimental stone tools that were found at naturally occurring tool-use sites. Our data were not collected by direct observation, but by inspecting stones after use. We found an association between stone mass and food type. In the tool tests, we found S-stones were chosen most often for attached oysters, and L-stones were chosen most often for unattached foods. L-stones were almost always chosen for larger unattached foods (greater than 3 cm length), while for smaller unattached foods (less than or equal to 3 cm length) selection was less skewed to L-stones and more evenly distributed between the M- and L-stone categories. In the non-experimental study, we found that mass varied significantly across five food categories (range: 16–5166 g). We reveal more detail on macaque stone tool mass than previous studies, showing that macaques select differing stone masses across a variety of tool-processed foods. Our study is the first step in investigating the behavioural and cognitive mechanisms that macaques are using during tool selection.