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41.
A three month experimental acidification was carried out on lotic bottom communities. Experiments were conducted under semi-natural conditions in plasticized wooden channels. Acidified communities (pH 4.0), with or without added aluminum, were compared with a reference community (pH 6.3–6.9). Added aluminum concentrations were respectively 0.2 and 0.4 mg 1–1 in experiments performed in 1982 and 1983. Water chemistry and taxonomic composition of the macroinvertebrate communities were monitored. Under acidified conditions, results were similar, with or without added aluminum. Mean abundances of all groups of organisms were lowered. Mayflies nearly completely disappeared from the acidified channels. The only organism not affected by the acidification was Microtendipes sp. Differences in the organism response were observed: Orthocladiinae (Rheocricotopus, Parametriocnemus, Corynoneura, Thienemanniella, Nanocladius, Cricotopus) and Ephemeroptera (Baetis, Habrophlebia, Habrophlebiodes, Paraleptophlebia, Ephemerella), especially early instars, were very sensitive to low pH, Chironomini and Tanypodinae were much less sensitive, while Tanytarsini were intermediate; Oligochaeta and Nematoda were difficult to classify, their response being different from one year to another. Organisms inhabiting the surface of artificial substrates disappeared very rapidly from the system, while those buried inside had a delayed reaction to acidification. Aluminum which was mainly in the monomeric form was not responsible for community modifications. Direct action of hydrogen ions through a physiological stress seems a more credible explanation. These results, induced by a continuous experimental acidification, suggest that if this small headwater stream undergoes acidification, the resulting invertebrate community will be very simplified, with only resistant species able to cope with the acid conditions. 相似文献
42.
Sodium-dependent high-affinity choline uptake was measured in various regions of the brains of rats irradiated for 45 min with either pulsed or continuous-wave low-level microwaves (2,450 MHz; power density, 1 mW/cm2; average whole-body specific absorption rate, 0.6 W/kg). Pulsed microwave irradiation (2-microseconds pulses, 500 pulses/s) decreased choline uptake in the hippocampus and frontal cortex but had no significant effect on the hypothalamus, striatum, and inferior colliculus. Pretreatment with a narcotic antagonist (naloxone or naltrexone; 1 mg/kg i.p.) blocked the effect of pulsed microwaves on hippocampal choline uptake but did not significantly alter the effect on the frontal cortex. Irradiation with continuous-wave microwaves did not significantly affect choline uptake in the hippocampus, striatum, and hypothalamus but decreased the uptake in the frontal cortex. The effect on the frontal cortex was not altered by pretreatment with narcotic antagonist. These data suggest that exposure to low-level pulsed or continuous-wave microwaves leads to changes in cholinergic functions in the brain. 相似文献
43.
Three different rhabdovirus isolates, eggplant mottled dwarf virus (EMDV), tomato veinyellowing virus (TVYV) and a hitherto undefined isolate from tomato in Portugal (Tom-P) were compared by two different serological techniques, immunosorbent electron microscopy (ISEM) and electro-blot-immunoassay (EBIA). Antisera were prepared either against purified virus or against partially purified virus preparations extracted by a one-step procedure. Even the partially purified virus preparations yielded antisera that allowed unequivocal identification of two of the five structural virus proteins, G and N, in EBIA and were suitable for specific trapping of complete virus particles on electron microscope grids. With both serological techniques identical results were obtained indicating a close serological relationship between the three isolates tested. Cross-reactions between the G proteins could be deduced from heterologous trapping of complete virus particles in ISEM. The cross-reactions for the G proteins were substantiated by the EBIA-results which indicated in addition cross-reactions between the remaining three major structural virus proteins, N, M1, and M2, but also revealed significant differences in the molecular weights of the G and M1 proteins between TVYV and the other two isolates. The results obtained indicate that Tom-P is serologically closely related and in respect of protein molecular weights identical to EMDV, and that TVYV is not a separate virus but rather a strain of EMDV. 相似文献
44.
Summary The pattern of the vascular supply to the choroid of the frog eye was studied in toto with the use of the injection-replication-SEM technique. The choroid of anuran amphibians is composed mainly of the choriocapillaris. In both species studied (Rana temporaria, Rana esculenta), an independent arterial supply to the choriocapillaris supplemented that from the ciliary arteries. This additional vascular route arises from the optic artery, a separate branch of the arteria infundibularis superficialis. The optic artery, accompanied by its vein within the vascular sheath of the optic nerve, joins the rich arterial capillary network of the choriocapillaris and supplies the posterior pole of the ocular bulb. The superficial capillary network displays a dense collar around the entrance of the optic nerve into the eye and is composed of a circular meshwork of small capillaries, several layers deep. More peripherally, however, it becomes single layered. This capillary network, as a whole, establishes numerous connections with the adjacent choriocapillaris at the posterior pole of the ocular bulb. In anuran amphibians the complex arrangement of both arterial systems supporting the choriocapillaris may be regarded as a more complete equivalent of the short posterior ciliary arteries of mammals. 相似文献
45.
Summary The angioarchitecture of the superficial vascular hyaloid system (membrana vasculosa retinae) of the frog eye was studied by means of scanning electron microscopy of vascular corrosion casts. The terminal vessels form a single-layered sheath intimately adjacent to the vitreal side of the avascular retina. The hyaloid system is subdivided by the ventral venous trunk into three central areas: the dorsal, the temporo-ventral, and the naso-ventral area. Toward the ora serrata, the hyaloid system is bordered by an arterial ring, and by nasal and temporal venous branches forming more or less complete hemicircles. A vascular zone composed of several tongue-like sectors establishes an inter-connection between the peripheral vascular rings and the central areas of the fundus. The arterial blood is supplied from the arterial ring. The drainage of the hyaloid system is provided via two routes: (1) the Y-shaped ventral trunk collects blood from the central areas, (2) the two peripheral venous branches drain the tongue-like sectors. The vessels within the dorsal area follow preferentially a dorso-ventral meridional direction. This densely capillarized territory corresponds in localization to the area centralis retinae. The ultrastructure of microvessels of the hyaloid system is characterized by features typical for capillaries of the central nervous system. 相似文献
46.
J. Guy Dr. O. Bosler G. Dusticier G. Pelletier A. Calas 《Cell and tissue research》1987,250(3):657-662
Summary The morphological substrate of putative serotonin (5-HT)/neuropeptide Y (NPY) interactions in thé suprachiasmatic nucleus (SCN) was investigated by combined radioautography and immunocytochemistry after intraventricular administration of (3H)5-HT in the rat. In the ventral portion of the SCN, the distribution of (3H)5-HT uptake sites overlapped closely the NPY-immunoreactive terminals. Previous investigations have shown that the dense 5-HT and NPY innervations of the SCN originate in different structures, i.e., the midbrain raphe nuclei and the ventral lateral geniculate nucleus, respectively. Accordingly, in the present study, destruction of 5-HT afferents by 5,7-dihydroxytryptamine was not found to induce any modification in NPY staining and, in ultrastructural immuno-radioautographic preparations, two distinct pools of axonal varicosities could be identified. Both 5-HT and NPY terminals established morphologically defined synaptic junctions, sometimes on the same neuronal target. Some cases of direct axo-axonic appositions between the two types of terminals were also encountered. These data constitute additional criteria for characterizing the cytological basis of the multiple transmitter interactions presumably involved in the function of the SCN as a central regulator of circadian biological rhythms. 相似文献
47.
48.
Joseph C. Polacco Adam K. Judd Jody K. Dybing Silvia R. Cianzio 《Molecular & general genetics : MGG》1989,217(2-3):257-262
Summary We reported earlier the recovery of two classes of soybean urease mutants in soybean (Glycine max L. Merr. cv. Williams). Class I mutants lack the embryo-specific urease while class II mutants lack the activities of both
urease isozymes, the embryo-specific and the ubiquitous urease, the latter found in all tissues examined. We report here the
recovery of a true-breeding mutant, aj3, which represents the third phenotypic class: normal levels of embryo-specific urease
and little or no ubiquitous urease. Unlike class II mutant plants which lack urease in all tissue, aj3 lacks urease activity
only in leaves (ca. 2% normal activity); its roots have near normal urease activity. Callus derived from leaves of aj3 has
14% to 40% the urease activity of Williams 82 callus. This partial reduction in urease activity in aj3 callus is sufficient
to reduce growth with urea as sole nitrogen source and to confer resistance to 50 mM urea added to callus maintenance medium.
Leaves of aj3 produce more than 40 times the urease antigen expected from their urease activity. The aj3 trait is due to a
single recessive lesion which is not allelic with lesions at theEu2, Eu3 (class II) orEu1 (class I) loci. We designate the aj3 genotype aseu4/eu4. 相似文献
49.
50.
Filter types, filtration and post-filtration treatment in phytoplankton production studies 总被引:1,自引:0,他引:1
Acid rinsing, used to decontaminate filters in 14C productionstudies, caused cell rupture and resulted in elevated 14C countsin the filtrates of six out of seven phytoplankton samples.Large volume (50 ml) rinses using only water caused some, butlesser, damage. Comparing the recovery of 14C-labelled cellsand chlorophyll a on glass-fibre, polycarbonate and celluloseester filters revealed unaccountable losses at times with allthree filter types. These losses could not be explained by cellrupture, attachment to the filter funnel wall, filter treatmentor self-absorption during scintillation counting. Compared tothe whole sample acid bubbling method, recovery on the glass-fibrefilters was highest. Results for the polycarbonate filters weremore variable, while, in all cases, recovery on cellulose esterfilters was much lower. 相似文献