Compatible plant-aphid interactions: How aphids manipulate plant responses

To access phloem sap, aphids have developed a furtive strategy, their stylets progressing towards sieve tubes mainly through the apoplasmic compartment. Aphid feeding requires that they overcome a number of plant responses, ranging from sieve tube occlusion and activation of phytohormone-signalling pathways to expression of anti-insect molecules. In addition to bypassing plant defences, aphids have been shown to affect plant primary metabolism, which could be a strategy to improve phloem sap composition in nutrients required for their growth. During compatible interactions, leading to successful feeding and reproduction, aphids cause alterations in their host plant, including morphological changes, modified resource allocation and various local as well as systemic symptoms. Repeated salivary secretions injected from the first probe in the epidermal tissue up to ingestion of sieve-tube sap may play a crucial role in the compatibility between the aphid and the plant.     

Haemodynamic effects of macrocyclic and linear gadolinium chelates in rats: role of calcium and transmetallation

Several studies were undertaken to compare four magnetic resonance imaging (MRI) contrast media (CM) as regards acute haemodynamic effects in rats and to investigate the mechanisms involved. (1) Normotensive rats received a rapid bolus intravenous injection of 0.5 mmol kg of each CM. The effects of Gd-DOTA, Gd-HP-DO3A, Gd-DTPA and Gd-DTPA-BMA on blood pressure (BP) were compared. (2) The haemo-dynamic effects of Gd-DTPA (0.5 mmol kg ) were compared to those of isovolumic and isoosmolar Zn-DTPA and glucose solutions. (3) The haemodynamic profiles of Gd-DTPA and Gd-DTPA-BMA were recorded with and without addition of ionized calcium. (4) The mechanism of Gd-HP-DO3A-induced tran-sient rise in BP was investigated by evaluating the effects of phentolamine or diltiazem pretreatment. For (1) the greatest drop in BP occurred following Gd-DTPA (a linear chelate) injection (–18 ± 2% vs base-line, P < 0.01). Gd-DTPA-BMA, another lineate chelate, also induced a slight but significant reduction in BP (–8 ± 2% at 45 s, P < 0.05). Gd-DOTA, a macrocyclic CM, had virtually no haemodynamic effects. For (2) the Gd-DTPA-induced drop in BP was greater than that of the osmolality-matched glucose control and lower than that of osmolality-matched Zn-DTPA. For (3) a transmetallation phenomenon versus free ionized calcium is possible in the case of both linear CM (Gd-DTPA and Gd-DTPA-BMA) since Ca significantly reduced the CM-induced decrease in BP. For (4) a transient rise in BP was observed following Gd-HP-DO3A, another macrocyclic chelate, associated with a concomitant increase in stroke volume. This effect was antagonized neither by phentolamine nor by diltiazem. The decrease in BP following injection of Gd-DTPA or Gd-DTPA-BMA may not only be osmolality-related since (a) Gd-DOTA solution, whose osmo-lality is greater than that of Gd-DTPA-BMA, had a lesser effect, and (b) this hypotensive effect was corrected by addition of ionized calcium. The transient Gd-HP-DO3A-induced rise in BP is probably the consequence of a positive inotropic effect. © Rapid Science 1998     

Asymmetric distribution of the plasma-membrane H+-ATPase in embryos of Vicia faba L. with special reference to transfer cells

The ultrastructural localization of the plasma-membrane H⁺ -ATPase by immunocytochemistry was studied in Vicia faba embryos which absorb nutrients from the maternal organism through the transfer cells of their external epidermis. The samples were embedded in LR White resin and the specificity of immunolabelling was checked by inhibition in the presence of purified H⁺-ATPase. The following results were obtained: (i) The H⁺-ATPase density varied according to the cell type, being higher in transfer cells than in other cell types, especially the non-modified cells of the internal epidermis. (ii) There was a marked polarity in transfer cells as proton pumps were more numerous in the area of plasmalemma infoldings where active nutrient uptake is assumed to take place, (iii) No clear immunolabelling occurred on the plasma membrane of plasmodesmata. These results demonstrate that in transfer cells the area of plasmalemma infoldings is highly specialized for active solute transport; they also support the idea of specific structural properties of the plasmalemma in plasmodesmata.This work was supported by the Centre National de la Recherche Scientifique (URA CNRS 574). We express our gratitude to Dr M.G. Palmgren (Royal Veterinary and Agricultural University, Copenhagen, Denmark) for his gift of purified H⁺-ATPase. We wish to thank J.C. Fromont for his skillful technical assistance with the immunological procedures. We are grateful to J.M. Perault and C. Besse of the Electron Microscopy Service (Service Universitaire de Microscopie Electronique Appliquée à la Biologie Poitiers, France) for their contribution to the microscopical techniques.     

Cell-to-cell transfer of glial proteins to the squid giant axon: The glia- neuron protein transfer hypothesis

The hypothesis that glial cells synthesize proteins which are transferred to adjacent neurons was evaluated in the giant fiber of the squid (Loligo pealei). When giant fibers are separated from their neuron cell bodies and incubated in the presence of radioactive amino acids, labeled proteins appear in the glial cells and axoplasm. Labeled axonal proteins were detected by three methods: extrusion of the axoplasm from the giant fiber, autoradiography, and perfusion of the giant fiber. This protein synthesis is completely inhibited by puromycin but is not affected by chloramphenicol. The following evidence indicates that the labeled axonal proteins are not synthesized within the axon itself. (a) The axon does not contain a significant amount of ribosomes or ribosomal RNA. (b) Isolated axoplasm did not incorporate [(3)H]leucine into proteins. (c) Injection of Rnase into the giant axon did not reduce the appearance of newly synthesized proteins in the axoplasm of the giant fiber. These findings, coupled with other evidence, have led us to conclude that the adaxonal glial cells synthesize a class of proteins which are transferred to the giant axon. Analysis of the kinetics of this phenomenon indicates that some proteins are transferred to the axon within minutes of their synthesis in the glial cells. One or more of the steps in the transfer process appear to involve Ca++, since replacement of extracellular Ca++ by either Mg++ or Co++ significantly reduces the appearance of labeled proteins in the axon. A substantial fraction of newly synthesized glial proteins, possibly as much as 40 percent, are transferred to the giant axon. These proteins are heterogeneous and range in size from 12,000 to greater than 200,000 daltons. Comparisons of the amount of amino acid incorporation in glia cells and neuron cell bodies raise the possibility that the adaxonal glial cells may provide an important source of axonal proteins which is supplemental to that provided by axonal transport from the cell body. These findings are discussed with reference to a possible trophic effect of glia on neurons and metabolic cooperation between adaxonal glia and the axon.     

A modular treatment of molecular traffic through the active site of cholinesterase

We present a model for the molecular traffic of ligands, substrates, and products through the active site of cholinesterases (ChEs). First, we describe a common treatment of the diffusion to a buried active site of cationic and neutral species. We then explain the specificity of ChEs for cationic ligands and substrates by introducing two additional components to this common treatment. The first module is a surface trap for cationic species at the entrance to the active-site gorge that operates through local, short-range electrostatic interactions and is independent of ionic strength. The second module is an ionic-strength-dependent steering mechanism generated by long-range electrostatic interactions arising from the overall distribution of charges in ChEs. Our calculations show that diffusion of charged ligands relative to neutral isosteric analogs is enhanced approximately 10-fold by the surface trap, while electrostatic steering contributes only a 1.5- to 2-fold rate enhancement at physiological salt concentration. We model clearance of cationic products from the active-site gorge as analogous to the escape of a particle from a one-dimensional well in the presence of a linear electrostatic potential. We evaluate the potential inside the gorge and provide evidence that while contributing to the steering of cationic species toward the active site, it does not appreciably retard their clearance. This optimal fine-tuning of global and local electrostatic interactions endows ChEs with maximum catalytic efficiency and specificity for a positively charged substrate, while at the same time not hindering clearance of the positively charged products.     

哈尔滨西郊赤狐冬季巢区的初步研究

本文利用雪地跟踪方法对哈尔滨西郊5只赤狐在1985-1986年冬季的巢区做了观察。结果表明,5只狐对巢区内各部分使用的强度是不等的,对巢区中部的某些地块使用强度要高于对外围的使用,并具有明显的方向性。5个巢区的平均活动半径为320±68米至557±82米,面积为1.44-4.O9平方公里,线性指数为1.079至2。5只狐相邻距离约1000米。