Alteration of stimulus-specific guard cell calcium oscillations and stomatal closing in Arabidopsis det3 mutant

Cytosolic calcium oscillations control signaling in animal cells, whereas in plants their importance remains largely unknown. In wild-type Arabidopsis guard cells abscisic acid, oxidative stress, cold, and external calcium elicited cytosolic calcium oscillations of differing amplitudes and frequencies and induced stomatal closure. In guard cells of the V-ATPase mutant det3, external calcium and oxidative stress elicited prolonged calcium increases, which did not oscillate, and stomatal closure was abolished. Conversely, cold and abscisic acid elicited calcium oscillations in det3, and stomatal closure occurred normally. Moreover, in det3 guard cells, experimentally imposing external calcium-induced oscillations rescued stomatal closure. These data provide genetic evidence that stimulus-specific calcium oscillations are necessary for stomatal closure.     

Multicolor and electron microscopic imaging of connexin trafficking

Recombinant proteins containing tetracysteine tags can be successively labeled in living cells with different colors of biarsenical fluorophores so that older and younger protein molecules can be sharply distinguished by both fluorescence and electron microscopy. Here we used this approach to show that newly synthesized connexin43 was transported predominantly in 100- to 150-nanometer vesicles to the plasma membrane and incorporated at the periphery of existing gap junctions, whereas older connexins were removed from the center of the plaques into pleiomorphic vesicles of widely varying sizes. Selective imaging by correlated optical and electron microscopy of protein molecules of known ages will clarify fundamental processes of protein trafficking in situ.     

Calcium rises abruptly and briefly throughout the cell at the onset of anaphase

Continuous measurement and imaging of the intracellular free calcium ion concentration ([Ca2+]i) of mitotic and interphase PtK1 cells was accomplished with the new fluorescent Ca2+ indicator fura-2. No statistically significant difference between basal [Ca2+]i of interphase and mitotic cells was detected. However, mitotic cells showed a rapid elevation of [Ca2+]i from basal levels of 130 nM to 500 to 800 nM at the metaphase-anaphase transition. The [Ca2+]i transient was brief, lasting approximately 20 seconds and the elevated [Ca2+]i appeared uniformly distributed over the entire spindle and central region of the cell. The close temporal association of the [Ca2+]i transient with the onset of anaphase suggests that calcium may have a signaling role in this event.     

Epilithic biofilm as a key factor for small‐scale river fisheries on Caribbean islands

Abstract Numerous freshwater species are consumed or exploited through artisanal fisheries in the rivers of the islands of Guadeloupe, French West Indies. Autochthonous production of organic matter is limited in these flowing rivers and is mainly represented by scarce filamentous green algae and an abundant epilithic biofilm growing on wet stones in the river bed. Stable isotope analysis was used to quantify the relative importance of biofilm and other riverine allochthonous and autochthonous food sources in the diet of tropical shrimps (Palaemonidae, Atyidae and Xiphocarididae) and fishes (Gobiidae and Eleotridae) consumed by the local people. The epilithic biofilm was exploited by most species, constituted an important source of autochthonous carbon and was an important source of organic matter production at the base of freshwater food webs in Caribbean rivers. Biofilm percentages in the diet reached 32% for molluscs, 85% for atyid shrimps, 29% for xiphocaridid shrimps, 14% for palaemonid shrimps and 13% for fish. Assessment of biofilm in nine rivers showed that blue and red cyanobacteria were quantitatively dominant with a moderately rich diatom flora. These results address the interactions between river biofilm and Caribbean freshwater fauna where trophic links between consumers and their potential resources have poorly been documented.     

新《兽药管理条例》实施过程中存在的难点

介绍了新<兽药管理条例>在当前兽药管理实践中存在的难点和问题,提出了解决这些问题的建议和措施.     

Calcium channels in planar lipid bilayers: insights into mechanisms of ion permeation and gating

Electrophysiological recordings were used to analyze single calcium channels in planar lipid bilayers after membranes from bovine cardiac sarcolemmal vesicles had been incorporated into the bilayer. In these cell-free conditions, channels in the bilayer showed unitary barium or calcium conductances, gating kinetics, and pharmacological responses that were similar to dihydropyridine-sensitive calcium channels in intact cells. The open channel current varied in a nonlinear manner with voltage under asymmetric (that is, physiological) ionic conditions. However, with identical solutions on both sides of the bilayer, the current-voltage relation was linear. In matched experiments, calcium channels from skeletal muscle T-tubules differed significantly from cardiac calcium channels in their conductance properties and gating kinetics.     

Effect of stale seedbed preparations and subsequent weed control in lettuce (cv. Iceboll) on weed densities

The effects of stale seedbed preparations and several weed control methods on the emergence of weeds in lettuce were studied. The specific goal was to evaluate the use of a stale seedbed in combination with chemical or mechanical weed control methods in the field. Depending on location and year, stale seedbed preparations followed by weed control prior to planting reduced the amount of weeds during crop growth by 43–83%. Control of the emerged seedlings after a stale seedbed preparation was more effective with glyphosate than with a rotary harrow. Covering the rotary harrow during control to prevent light reaching the soil improved its effect on the weed density during crop growth in two of 3 years. Radiation with far red light (FR) did not reduce the number of emerging weeds in this study. Mechanical control by finger weeder, torsion weeder and hoe was applied without stale seedbed preparations. These measures reduced the weed densities by 88–99%, compared with the untreated control and were more effective than chemical weed control with carbetamide and chlorpropham. The results show that the stale seedbed technique in combination with mechanical control of emerging weeds can reduce the weed population during crop growth as effectively as chemical control. The technique may therefore help reduce the use of herbicides in lettuce crops in the future.     

Adrenaline: mechanism of action on the pacemaker potential in cardiac Purkinje fibers

The pacemaker potential in Purkinje fibers is generated by a slow fall in potassium current which allows the inward background currents to depolarize the membrane. Adrenaline shifts the relation between activation of the potassium current and membrane potential in a depolarizing direction. Consequently, during the pacemaker potential, the potassium current falls more rapidly to lower values and the inward currents then depolarize the membrane more quickly. The shift in the potassium activation curve produced by adrenaline is large compared to that produced by calcium ions. The molecular action of adrenaline may involve either a large change in the surface charge of the membrane or a change in the dependence of the potassium permeability on the local electric field.