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931.
Two distinct small-subunit ribosomal RNA genes (SSU rDNAs), termed the “A gene” and “B gene,” were recently found in the toxic dinoflagellate Alexandrium fundyense Balech. A restriction fragment length polymorphism (RFLP) assay was developed to rapidly detect the A and B genetic markers. SSU rDNA from 58 cultures with species designations of A. tamarense (Lebour) Balech, A. catenella (Whedon et Kofoid) Balech, A. fundyense, A. affine (Fukuyo et Inoue)Balech, A. minutum Halim, A. lusitanicum Balech, and A. andersoni Balech were screened. These cultures represent toxic and non-toxic isolates from North America, western Europe, Thailand, Japan, Australia, and the ballast water of several cargo ships. The RFLP assay revealed five distinct groups. Three subdivided the A. tamarense/catenella/fundyense“species complex” into clusters defined by geographic origin, not by morphospecies designations. The fourth group consisted of A. affine, whereas the fifth group was represented by A. minutum, A. lusitanicum, and A. andersoni. The B gene was only found in A. tamarense, A. catenella, and A. fundyense, but not in all isolates. However, all North American isolates of this closely related group harbored this gene, and it also was found in some A. tamarense from scattered locations in Japan and in the ballast water of one ship that operated exclusively between Japan and Australia. Isolates without the B gene appeared to have only a single class of SSU rDNA. The B sequence was not essential for toxin production, but thus far those organisms harboring it were toxic. The A. tamarense/catenella/fundyense complex is composed of genetically distinct populations, within which may exist two or all three of the mophotypically defined species. The B gene is a promising taxonomic and biogeographic marker and may be useful for tracking the regional and/or global dispersal of particular populations. 相似文献
932.
Red squirrels (Tamiasciurus hudsonicus) defend food-based territoriesyear round, and juveniles must acquire a territory before winterto survive. We experimentally removed territory owners duringthe time that juveniles were becoming independent to examinethe effect of local vacancies on dispersal patterns. Juvenilesattempted to take over removal territories most frequently.However, females with offspring still on the natal territoryactually took over twice as many territories as juveniles. Thesefemales did not appear to move because of low reproductive potentialor to increase territory quality. Instead, moving to a removalterritory allowed more of their offspring to remain on the natalterritory, which appeared to increase juvenile survival. 相似文献
933.
Laura S. Rhoads Anne M. Danks IM John Anne Warner Robert L. Isaacson John Baust Robert G. Van Buskirk 《In vitro cellular & developmental biology. Animal》1993,29(3):208-214
Summary The possible role of extracellular calcium ([Ca+2]e) in cryopreservation-induced cytotoxicity was tested using Madin-Darby canine kidney (MDCK) cells and a fluorescent multiple
endpoint assay. MDCK cells maintained in 2 mM [Ca+2]e and treated with the calcium ionophore, ionomycin, increased their intracellular calcium ([Ca+2]i) as revealed by the calcium indicator dye, Fluo3 and the bottom-reading spectrofluorometer, CytoFluor 2300. The addition
of 10 mM [ethylene bis (oxyethylenenitrilo)]-tetraacetic acid (EGTA) to the extracellular medium before treatment with ionomycin blocked
this ionomycin-dependent increase in [Ca+2]i. A number of site and activity-specific fluorescent probes were surveyed to determine which indicator dye might best reveal
the ionomycin-induced cytotoxic events during this increase in [Ca+2]i. Although most dyes changed their emission profiles in response to calcium, neutral red was found to best reflect the loss
of [Ca+2]i homeostasis. The NR50 for a 15-min exposure to ionomycin in the presence of 2 mM [Ca+2]e was approximately 2μM ionomycin, but ionomycin had little apparent effect on neutral red retention when 10 mM EGTA was added to the extracellular medium. Thus it was clear that an increase in [Ca+2]i could be cytotoxic to MDCK cells and that neutral red could monitor this cytotoxic episode. To test if [Ca+2]e was similarly cytotoxic during cryopreservation, MDCK cells were subjected to cryopreservation in the presence of dimethylsulfoxide
(DMSO). In contrast to previous studies, plasma membrane integrity, not lysosomal function, seemed to best correlate with
cell survival subsequent to cryopreservation. In addition, decreasing [Ca+2]e had no discernable effect on the retention of plasma membrane indicator dyes, neutral red, or cell survival. It is concluded
that a) plasma membrane indicator dyes, not neutral red, might be better indicators of cytotoxicity occurring during cryopreservation;
b) DMSO might be toxic to lysosomes during cryopreservation of cultured cells; and c) although [Ca+2]e can contribute to cytotoxicity, the presence of [Ca+2]e might not influence cryopreservation-induced cytotoxicity. 相似文献
934.
Synopsis Disease-free blue tilapia,Oreochromis aureus, exposed to cadmium (0.5 ppm and 10 ppm) showed very significant and dramatic decrease in food consumptions. Food consumptions
returned to near normal 21 days after fish were returned to cadmium-free water. Along with anorexia there were decreases in
body weights during the period when fish were exposed to cadmium. Fish in cadmium-free water that were pair-fed to cadmium-exposed
fish (0.5 ppm) did not gain weight but there were no decreases in body weights. Cadmium was still in tissues 34 days after
the fish were placed in cadmium-free water and the accumulation was highest in the kidney; this was followed by liver, brain,
gill filaments and muscles. The accumulations of the heavy metal (in kidneys and gills) were significantly higher in fish
exposed to high than low cadmium levels. There were no differences in complement levels (haemolytic acitivity) in cadmium-exposed
and cadmium-free fish. However, cadmium-exposed fish did not produce detectable haemagglutinating antibodies against sheep
red blood cells while cadmium-free fish responded well to the antigen. The anorexia in cadmium-exposed fish contributed to
the depression in antibody production. 相似文献
935.
To explore the control effect of bait broadcasting by unmanned aerial vehicles (UAVs) on the imported fire ant Solenopsis invicta and evaluate its impact on biodiversity, we tested the drop flow rate and broadcasting evenness of fire ant baits with bait exit hatch sizes, as well as the dynamics of fire ants and other ants when different amounts of bait were used. The amount of bait applied per hectare was 6000–15,000 g in orchards. Fourteen days after broadcasting, the control effect of broadcasting 12,000 g and 15,000 g bait per hectare on active mounds and workers reached 90%, which was significantly higher than that achieved with 6000 g and 9000 g. After the application of bait, the number and species of other ants decreased and then increased; this was reflected in changes in the Shannon–Wiener index (H′), Pielou evenness index (E) and Simpson dominance index (C). The results of this study suggest that broadcasting bait by UAVs can achieve good control of S. invicta, and a reduction in native ant diversity can be achieved in the short term. 相似文献
936.
Sexual cycle and seasonal changes in the ovary of the red mullet, Mullus surmuletus, from the southern coast of Brittany 总被引:1,自引:0,他引:1
The reproductive cycle of the red mullet is described on a macroscopic scale in terms of the GSI, HSI and K , and on a microscopic scale in terms of histological changes in the ovary and changes in the oocyte size frequency distribution. On the southern coast of Brittany the red mullet breeds in May and June. During oogenesis, the previtellogenic period lasts 6 months and the secondary phase of vitellogenesis no more than 3 months. When spawning commences the process of vitellogenesis ceases and up to 20% of the vitellogenic oocytes become atretic. Prior to spawning a single batch of oocytes can be seen to be entering secondary vitellogenesis. During the immediate prespawning and spawning periods the existing vitellogenic oocytes mature but there is no recruitment from the stock of previteilogenic oocytes. This results in a gap or hiatus in the oocyte size frequency distribution between previtellogenic and vitellogenic oocytes within which there are very few resting or maturing oocytes. The red mullet appears to be a determinate spawner, in which egg loss through atresia considerably reduces the potential fecundity. 相似文献
937.
Effect of sink size on photosynthesis and carbohydrate content of leaves of three spring wheat varieties 总被引:3,自引:0,他引:3
R. Martínez-Carraseo E. Cervantes P. Pérez R. Morcuende I. M. Martín del Molino 《Physiologia plantarum》1993,89(3):453-459
Effects of CO2 on stomatal movements of Commelina communis L. were studied with plants, epidermal strips and guard cell protoplasts. With plants, the stomatal response induced by a blue light pulse was studied for different ambient CO2 concentration ranging from CO2 -deprived air to 100 Pa in darkness or under red light. It was observed that the blue light response could be obtained not only under a red light background but also in darkness and CO2 -free air, the two responses being quite similar.
With epidermal strips, the effect of CO2 on ferricyanide reductase activity at the guard cell plasmalemma was studied by transmission electron microscopy. In the presence of ferric ions, reduced ferricyanide gives an electron dense precipitate of Prussian Blue. In darkness and air, no precipitate was observed. In darkness and CO2 -free air as well as under light and normal air, a precipitate was found along the plasmalemma of the guard cells, indicating a ferricyanide reductase activity. With guard cell protoplasts suspended in a medium either in equilibrium with air or in a CO2 -free medium the H+ extrusion induced by a blue light pulse added to a red light background was measured. A low CO2 content was obtained by adding photosynthetic algae to the suspension of guard cell protoplasts. In a CO2 -free medium the rate of H+ extrusion was enhanced.
The results are discussed on the basis of a possible competition for reducing power between CO2 fixation and a putative blue light dependent redox chain located on the plasma membrane. 相似文献
With epidermal strips, the effect of CO
The results are discussed on the basis of a possible competition for reducing power between CO
938.
Summary In 20 of 22 study colonies, Homoptera-tending workers of the thatch antsFormica obscuripes andF. planipilis exhibited a significant size-distance relation, with smallest tenders working closest to the primary nest. No such relation was observed in scavengers working over the same range of distances in any of the 22 colonies. This paper describes the size-distance relation in tenders quantitatively, examines its expression given variation in Homoptera distribution, and compares it to similar patterns observed in otherF. rufa-group species. Three hypotheses on the adaptive significance of the size-distance relation are discussed: that the relation increases energetic efficiency, improves colony defense, or decreases the rate of getting lost in smaller tenders. 相似文献
939.
Summary Previous work showed that amiloride partially inhibits the net gain of Na in cold-stored red cells of guinea pig and that the proportion of unidirectional Na influx sensitive to amiloride increases dramatically with cooling. This study shows that at 37°C amiloride-sensitive (AS) Na influx in guinea pig red blood cells is activated by cytoplasmic H+, hypertonic incubation, phorbol ester in the presence of extracellular Cat2+ and is correlated with cation-dependent H+ loss from acidified cells. Cytoplasmic acidification increases AS Na efflux into Na-free medium. These properties are consistent with the presence of a Na-H exchanger with a H+ regulatory site. Elevation of cytoplasmic free Mg2– above 3 mm greatly increases AS Na influx: this correlates with a Na-dependent loss of Mg2–, indicating the presence of a Na-Mg exchanger.At 20°C activators of Na-H exchange have little or no further stimulatory effect on the already elevated AS Na influx. AS Na influx is much larger than either Na-dependent H+ loss or AS Na efflux at 20°C. The affinity of the AS Na influx for cytoplasmic H+ is greater at 20°C than at 37°C. Depletion of cytoplasmic Mg2+ does not abolish the high AS Na influx at 20°C.Thus, elevation of AS Na influx with cooling appears to be due to increased activity of a Na-H exchanger (operating in a slippage mode) caused by greater sensitivity to H+ at a regulatory site. 相似文献
940.
Frans H. M. M. van de Put Joost G. J. Hoenderop Jan Joep H. H. M. De Pont Peter H. G. M. Willems 《The Journal of membrane biology》1993,135(2):153-163
Rabbit pancreatic acinar cells, permeabilized by saponin treatment, rapidly accumulated 3.5 nmol of Ca2+/mg protein in an energy-dependent pool when incubated at an ambient free Ca2+ concentration of 100 nm. Maximal loading of the internal stores was reached at 10 min and remained unchanged thereafter. Complete inhibition of the Ca2+ pump with thapsigargin revealed that this plateau was the result of a steady-state between slow Ca2+ efflux and ATP-driven Ca2+ uptake. Sixty percent of the pool could be released by Ins(1,4,5)P3, whereas GTP released another twenty percent. The striking finding of this study is that the energy-dependent store could also be released by ruthenium red. Uptake experiments in the presence of ruthenium red revealed that the dye, at concentrations below 100 m, selectively reduced the size of the Ins(1,4,5)P3-releasable pool. Ruthenium red had no effect on the half-maximal stimulatory concentration of Ins(1,4,5)P3. At concentrations beyond 100 m, the dye also affected the GTP-releasable pool. Comparison with thapsigargin revealed that ruthenium red released Ca2+ from stores loaded to steady-state at a rate markedly faster than can be explained by inhibition of the ATPase alone. From the data presented, we concluded that ruthenium red selectively releases Ca2+ from the Ins(1,4,5)P3-sensitive store by activating a Ca2+ release channel, whereas Ca2+ release from the GTP-sensitive store is predominantly caused by inhibition of the Ca2+ pump. The postulated ruthenium red-sensitive Ca2+ release channel might be similar to the ryanodine-receptor in muscle.The research of Dr. P.H.G.M. Willems has been made possible by a fellowship of the Royal Netherlands Academy of Arts and Sciences. 相似文献