三种绿叶挥发性物质对云南切梢小蠹寄主定位行为的干扰作用

为了研究环境中非寄主阔叶植物释放出的绿叶挥发性物质（GLVs）对针叶树蛀干害虫云南切梢小蠹Tomicus yunnanesis的影响, 选取了(E)-2-己烯醛、 (E)-2-己烯醇和(Z)-3-己烯醇3种释放量较大的绿叶挥发性物质, 通过室内松梢取食试验测试了单组分及两两混合后对云南切梢小蠹寄主定位行为的干扰作用。结果表明： 源于阔叶植物的3种绿叶挥发性物质及其混合物能够不同程度干扰云南切梢小蠹的寄主定位行为。当虫放入广口瓶12 h后, 3个单组分绿叶挥发性物质处理组［A： (E)-2-己烯醛, P＜0.01; B： (E)-2-己烯醇, P＜0.01; C： (Z)-3-己烯醇, P＜0.01］及2个混合组分［D： (E)-2-己烯醛+(E)-2-己烯醇, P＜0.01）; E： (E)-2-己烯醛+(Z)-3-己烯醇, P＜0.01］中滞留在松梢外部的虫数与对照组相比都有显著性差异, 绿叶挥发性物质的存在显著降低了云南切梢小蠹侵害云南松松梢的概率。但是, 24 h后只有D组（P＜0.01）和E组（P＜0.01）滞留在松梢外部的虫数与对照组相比具有显著性差异, 在48 h后只有D组（P＜0.01）与对照相比仍具有显著性差异。本研究为利用非寄主植物的次生代谢产物防治云南切梢小蠹进行了有益的探索。     

Solution structure of an alternate conformation of helix27 from Escherichia coli16S rRNA

Helix (H)27 of 16S ribosomal (r)RNA from Escherichia coli was dubbed the "switch helix" when mutagenesis suggested that two alternative base pair registers may have distinct functional roles in the bacterial ribosome. Although more recent genetic analyses suggest that H27 conformational switching is not required for translation, previous solution studies demonstrated that the isolated E. coli H27 can dynamically convert between the 885 and 888 conformations. Here, we have solved the nuclear magnetic resonance solution structure of a locked 888 conformation. NOE and residual dipolar coupling restraints reveal an architecture that markedly differs from that of the 885 conformation found in crystal structures of the bacterial ribosome. In place of the loop E motif that characterizes the 885 conformer and that the 888 conformer cannot adopt, we find evidence for an asymmetrical A-rich internal loop stabilized by stacking interactions among the unpaired A's. Comparison of the isolated H27 888 solution structure with the 885 crystal structure within the context of the ribosome suggests a difference in overall length of H27 that presents one plausible reason for the absence of H27 conformational switching within the sterically confining ribosome.     

Rice and Remittances: Crop Intensification Versus Labour Migration in Southern Laos

Despite being a low-income, agriculture-based country with a subsistence orientation, Laos is in the early stages of a major economic transformation whereby rural households have been experiencing rapid change in their farming and livelihood systems. Some households have begun to engage in semi-commercial farming while others have adopted labour-oriented or migration-oriented livelihood strategies. This paper explores how rural households in six villages in the lowlands of Champasak Province in southern Laos make a living. These villages vary in their access to irrigation and to markets. Nevertheless, in all villages, long-term migration of younger household members to neighbouring Thailand has come to play a large role in household livelihood strategies. In some cases this is necessary to meet the household’s consumption requirements; in most, it is part of a diversified strategy in which rice farming still plays a significant role, though still largely for subsistence. The paper examines some of the issues involved in attempting to promote intensive, market-oriented rice farming in a context of an emerging on-farm labour shortage combined with an increasing flow of remittances from migrant family members.     

Quasi-steady State Reduction of Molecular Motor-Based Models of Directed Intermittent Search

We present a quasi-steady state reduction of a linear reaction-hyperbolic master equation describing the directed intermittent search for a hidden target by a motor-driven particle moving on a one-dimensional filament track. The particle is injected at one end of the track and randomly switches between stationary search phases and mobile nonsearch phases that are biased in the anterograde direction. There is a finite possibility that the particle fails to find the target due to an absorbing boundary at the other end of the track. Such a scenario is exemplified by the motor-driven transport of vesicular cargo to synaptic targets located on the axon or dendrites of a neuron. The reduced model is described by a scalar Fokker–Planck (FP) equation, which has an additional inhomogeneous decay term that takes into account absorption by the target. The FP equation is used to compute the probability of finding the hidden target (hitting probability) and the corresponding conditional mean first passage time (MFPT) in terms of the effective drift velocity V, diffusivity D, and target absorption rate λ of the random search. The quasi-steady state reduction determines V, D, and λ in terms of the various biophysical parameters of the underlying motor transport model. We first apply our analysis to a simple 3-state model and show that our quasi-steady state reduction yields results that are in excellent agreement with Monte Carlo simulations of the full system under physiologically reasonable conditions. We then consider a more complex multiple motor model of bidirectional transport, in which opposing motors compete in a “tug-of-war”, and use this to explore how ATP concentration might regulate the delivery of cargo to synaptic targets.     

Small-angle X-ray scattering studies of 7S and 11S globulins from pea (Pisum sativum)

Small-angle X-ray scattering studies have been conducted on solutions of 11S and 7S globulins isolated from peas (Pisum sativum cv. Filby), and the radii of gyration and molecular weights determined. The general features of the scattering curves were similar to those reported for other seed storage proteins.     

Histamine and a guanine nucleotide increase calcium permeability in pig aortic microsomal fractions.

ATP-dependent Ca2+ accumulation was measured in pig aortic microsomal fractions containing plasmalemma and endoplasmic reticulum. In vesicles sonicated with histamine, to allow access to internally located receptor sites, guanosine 5'-[beta gamma-imido]triphosphate (p[NH]ppG), added to activate externally located guanine-nucleotide-transducing proteins, caused a concentration-dependent decrease in steady-state Ca2+ accumulation that was reversed by guanosine 5'-[beta-thio]diphosphate. In the presence of p[NH]ppG, sonication with histamine produced a concentration-dependent inhibition of Ca2+ accumulation that could be antagonized by the H1 antagonist mepyramine, but not by the H2 antagonist cimetidine. The inhibition of steady-state Ca2+ accumulation could have resulted from an inhibition of ATP-dependent Ca2+ uptake or a stimulation of Ca2+ release. We observed, however, that p[NH]ppG plus histamine stimulated, rather than inhibited, Ca2(+)-ATPase activity. We concluded that p[NH]ppG and histamine acted together to increase Ca2+ permeability. In support of this, p[NH]ppG accelerated efflux of Ca2+ from passively loaded vesicles sonicated with, but not without, histamine. The effect of p[NH]ppG was unlikely to be due to Ins(1,4,5)P3 (and hence release from endoplasmic-reticulum vesicles), since addition of Ins(1,4,5)P3 to vesicles sonicated with histamine did not alter steady-state Ca2+ accumulation. Our results therefore suggest that histamine and p[NH]ppG increased the permeability of the plasmalemma vesicles and may thus model the process of receptor-mediated Ca2+ entry into intact cells.     

Absolute rates of adenosine formation during ischaemia in rat and pigeon hearts.

1. The activities of ecto- and cytosolic 5'-nucleotidase (EC 3.1.3.5), adenosine kinase (EC 2.7.1.20), adenosine deaminase (EC 3.5.4.4) and AMP deaminase (EC 3.5.4.6) were compared in ventricular myocardium from man, rats, rabbits, guinea pigs, pigeons and turtles. The most striking variation was in the activity of the ecto-5'-nucleotidase, which was 20 times less active in rabbit heart and 300 times less active in pigeon heart than in rat heart. The cytochemical distribution of ecto-5'-nucleotidase was also highly variable between species. 2. Adenosine formation was quantified in pigeon and rat ventricular myocardium in the presence of inhibitors of adenosine kinase and adenosine deaminase. 3. Both adenosine formation rates and the proportion of ATP catabolized to adenosine were greatest during the first 2 min of total ischaemia at 37 degrees C. Adenosine formation rates were 410 +/- 40 nmol/min per g wet wt. in pigeon hearts and 470 +/- 60 nmol/min per g wet wt. in rat hearts. Formation of adenosine accounted for 46% of ATP plus ADP broken down in pigeon hearts and 88% in rat hearts. 4. The data show that, in both pigeon and rat hearts, adenosine is the major catabolite of ATP in the early stages of normothermic myocardial ischaemia. The activity of ecto-5'-nucleotidase in pigeon ventricle (16 +/- 4 nmol/min per g wet wt.) was insufficient to account for adenosine formation, indicating the existence of an alternative catabolic pathway.     

Inhibition of IMP-specific cytosolic 5''-nucleotidase and adenosine formation in rat polymorphonuclear leucocytes by 5''-deoxy-5''-isobutylthio derivatives of adenosine and inosine.

1. The partially purified IMP-specific cytosolic 5'-nucleotidases from rat liver, polymorphonuclear leucocytes and heart were inhibited by 50% by 2-6 mM-5'-deoxy-5'-isobutylthioadenosine (IBTA) or 7-10 mM-5'-deoxy-5'-isobutylthioinosine (IBTI). IBTA and IBTI inhibited the rat liver and polymorphonuclear-leucocyte enzymes non-competitively. IBTA, but not IBTI, also inhibited the ecto-5'-nucleotidase of polymorphonuclear leucocytes. IBTI was, by contrast, a more potent inhibitor than IBTA of the AMP-specific soluble 5'-nucleotidase from pigeon heart. 2. During 2-deoxyglucose-induced ATP-catabolism in rat polymorphonuclear leucocytes, adenosine formation was inhibited by approx. 80% by 3 mM-IBTA and by approx. 70% by 7 mM-IBTI. 3. The results show that 5'-modified nucleosides are inhibitors of cytosolic 5'-nucleotidases and that they penetrate to inhibit their target enzymes in intact cells. Such inhibitors may be useful to clarify the mechanisms of adenosine formation and to prevent mononucleotide hydrolysis during ATP breakdown.     

The existence and properties of two dimers of rat liver ecto-5''-nucleotidase.

Immunoaffinity-purified rat liver 5'-nucleotidase contained two subunits of Mr 70 000 (alpha) and 38 000 (beta). Charge-shift electrophoresis and chemical cross-linking revealed that approx. 80% of the solubilized enzyme activity occurred as an alpha alpha-dimer of Mr 140 000. The remaining 20% was an alpha beta-dimer of Mr 108 000. The beta-subunit did not possess enzymic activity. Peptide mapping and immunoblotting with antibodies against the alpha- and beta-subunits showed that the beta-subunit was homologous with a part of the alpha-subunit. Three monoclonal antibodies against rat liver 5'-nucleotidase were characterized as binding to the extracellular domain of the enzyme. All three monoclonal antibodies and concanavalin A bound to the alpha-subunit, but no binding could be detected to the beta-subunit. It was therefore concluded that the beta-subunit was a fragment of an alpha-subunit that had lost an extracellular domain. Both forms of the enzyme occurred in freshly solubilized membrane preparations as well.