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31.
32.
Phosphorus exchange at the sediment-water interface coupled with several parameters were assessed in several reservoirs with geologically different catchment basins and different trophic status in Morocco and France.The results showed that these exchanges were regulated by a combination of factors: physical chemical variability of the environment, the geological composition of catchment basins and the trophic status of the lake.In the hypereutrophic Villerest, iron-bound phosphorus is the major form of phosphorus trapped by the sediment whereas, in Moroccan reservoirs, calcium-bound phosphorus prevailed.We suggest that a drastic control of phosphorus inputs into the waters must be done through a large program of dephosphatization of tributaries to avoid Microcystis aeruginosa bloom formation in Villerest (Aleya et al., 1993) and calcium-bound phosphorus dissociation in Moroccan reservoirs with upward release of bioavailable phosphorus.
Résumé Les échanges de phosphore au niveau de l'interface eau-sédiment couplés á la distribution temporelle de divers éléments chimiques et biologiques ont été étudiés dans divers réservoirs de niveaux trophiques différents, au Maroc et en France.Nos résultats mettent clairement en évidence une influence directe de l'environnement physico-chimique, de la nature géologique des bassins versants et de l'état trophique du lac sur la dynamique du phosphore au sein de cette interface.De plus, il apparait que dans le lac hypereutrophe de Villerest (Roanne, France), le phosphore est majoritairement complexé au fer alors que dans les retenues marocaines, ce sont les complexes phosphore-calcium qui prédominent.Nous préconisons un contrôle drastique des apports en phosphore á travers l'installation et la multiplication d'unités de déphosphatation afin d'éviter d'une part, la prolifération massive de la Cyanobactérie Microcystis aeruginosa á Villetest (Aleya et al., 1994) et d'autre part la dissociation des complexes phhosphore-calcium au sein des retenues marocaines avec libération de phosphore biodisponible.相似文献
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Peter F. Daels Hussni Mohammed S. M. E. Montavon G. H. Stabenfeldt J. P. Hughes Kristina Odensvik H. Kindahl 《Animal reproduction science》1995,40(4):305-321
Repeated administration of prostaglandin is the treatment of choice for the termination of pregnancy in mares more than 40 days pregnant. Even though it is well documented that PGF-2 or analogue needs to be administered every 12–24 h for successful induction of abortion, little is known about the underlying endocrine changes and the mechanism by which abortion occurs. The aim of this study was to characterize the changes in PGF-2, progesterone and estrogen secretion during prostaglandin-induced abortion. Six mares, 82–102 days pregnant, were treated daily with 250 μg cloprostenol, blood was collected at 1-h intervals until fetal expulsion and pregnancy examination was performed daily. Four mares, 92–97 days pregnant, received no treatment but were subjected to the same hourly blood collections and daily genital examinations described for cloprostenol-treated mares for 3 days. Mean time from first cloprostenol administration until fetal expulsion was 48.6 ± 5.6 h and required 2.8 ± 0.2 cloprostenol administrations. In all mares, progesterone concentrations decreased in a near linear manner after the first cloprostenol administration and were invariably low (1.3 ± 0.2 ng ml−1, mean ± SEM) at the time of fetal expulsion. Mean estrogen secretion remained unchanged until 5 h before fetal expulsion and then decreased rapidly to non-pregnant levels. Endogenous PGF-2 secretion rate increased with each cloprostenol administration and culminated in sustained PGF-2 secretion which persisted until fetal expulsion was completed. From these results we conclude that cloprostenol-induced abortion is associated with endogenous PGF-2 secretion, fetal expulsion coincides with sustained PGF-2 secretion and low progesterone concentrations and plasma estrogen concentrations remain unchanged until hours before fetal expulsion. 相似文献
35.
人胚DA能神经元移植于帕金森氏病猴模型的TH免疫细胞化学的研究 总被引:3,自引:0,他引:3
为了对人胚黑质DA神经元移植治疗PD人的临床应用作出客观评估,将8-12周人胚黑质细胞移植到用MPTP诱发的偏侧PD猴新纹状体内。实验动物分别存活2个月、5个月和1年后,用TH免疫细胞化学方法对被移植的人胚DA细胞的存活和与宿主间的突触联系进行检查。在光镜下可见被移植侧的新纹状体内有TH阳性细胞,它们成小群散在分布,每小群有3-10个细胞。TH阳性细胞的轴突延伸到整个新纹状体,树突呈现出正常发育过 相似文献
36.
To fill in some of the gaps in our knowledge of Schizogony of Haemoproteus columbae Kruse, transmission experiments involving inoculation into pigeons (Columba livia Gmelin) of sporozonites from salivary glands of the hippoboscid fly Pseudolynchia canariensis (Macquart) were carried out. We were unable to detect prepatent schizonts or to observe schizogonic development when infection became chronic. Schizonts were mainly confined to lung tissue. Observations of parapatent schizonts were made in smears and tissue sections. A variety of forms was found. Cytomeres were rarely encountered. Two types of morphologically distinct merozoites were seen. One type was twice as large as large as the other and was thought to repeat the process of schizogony several times before invading erythrocytes. Schizonts with cytoplasmic clefts were not common in our material due to the fixatives used (Bouin's and Carnoy's). Merozoites were occasionally observed inside monocytes, probably being phagocytosed. 相似文献
37.
Treatment of 2,3,4,6-tetra-O-methyl-d-glucose with 10 molar equivalents ofn 30% aqueous hydrogen peroxide and 2 molar equivalents of potassium hydroxide afforded, after chromatographic separation, 2,3,4,6-tetra-O-methyl-d-gluconolactone. 1-O-formyl-2,3,5-tri-O-methyl-d-arabinose methyl hemiacetal (7), 2,3,5-tri-O-methyl-d-arabinonolactone, methyl 2,3,5-tri-O-methyl-d-arabinoside, O-(2,4-di-O-methyl-d-erythrose)-(1'→3)-2,4-di-O-methyl-d-erythronic acid, and O-(2,4-di-O-methyl-d-erythrose)-(1′→2)-3-O-methyl-d-glyceraldehyde. The proportions of the products depended on the reaction conditions, especially the time, temperature, and the presence or absence of magnesium hydroxide. Formation of the products is explained by a series of reactions beginning with the addition of hydrogen peroxide to the carbonyl form of the methylated sugar. The adduct, with the help of superoxide radical and a molecule of hydrogen peroxide, breaks up in two ways, giving 2,3,4,6-tetra-O-methyl-d-gluconic acid and 7. The formic ester, on hydrolysis, gives 2,3,5-tri-O-methyl-d-arabinose, which undergoes a similar series of reactions, affording 2,3,5-tri-O-methyl-d-arabinonic acid, and presumably, 1-O-formyl-2,4-di-O-methyl-d-erythrose methyl hemiacetal. Apparently, the latter compound, on hydrolysis, forms a dimer, which, with alkaline hydrogen peroxide, undergoes a similar series of reactions, ultimately affording O-(2,4-di-O-methyl-d-erythrose)-(1→3)-2,4-di-O-methyl-d-erythronic acid and O-(2,4-di-O-methyl-d-erythrose)-(1→2)-3-o-methyl-d-glyceraldehyde. With a larger amount of alkali, under more-severe conditions, oxidation of 2,3,4,6-tetra-O-methyl-d-glucose proceeds further, with production of up to 3 moles of formic acid per mole of methylated sugar. 相似文献
38.
A conjugation system initially discovered in beta-lactamase-producing gonococci mobilized small non-selftransmissible R plasmids encoding beta-lactamase (penicillinase) production into other gonococci, Neisseria, and Escherichia coli. This conjugation system was mediated by a separate selftransmissible plasmid of 23.9 X 10(6) daltons, pFA2. Conjugative plasmids capable of mobilizing R plasmids were also found in nearly 8% of the non-penicillinase-producing gonococci. These were similar to pFA2 in size, buoyant density, and restriction endonuclease digest patterns but were less efficient than pFA2 in mobilization of the penicillinase plasmid pFA3. The presence of conjugative plasmids in gonococci isolated before the appearance of penicillinase-producing strains indicates that a conjugation system for plasmid transfer predated the appearance of R plasmids in gonococci. 相似文献
39.
As determined by their ability to exflagellate and round up, it took the macrogametocyte and the microgametocyte of Haemoproteus columbae in pigeons 68 and 116 h, respectively, after patency to reach maturity. Pigment granules appeared in the undifferentiated gametocytes 8 h after invasion of blood. Vacuoles were observed in young gametocytes and persisted in the older forms. The growth curve of H. columbae is close to the sigmoidal curve for growth in protozoa. Multiple infection was noticed in pigeons with high levels of parasitemia, but no more than 2 gametocytes reached maturity; such multiple infections were rare in relapses. The sex ratio of the gametocytes was 1:1. Strong lateral displacement of the nuclei of infected erythrocytes was the rule; hypertrophy was negligible. 相似文献
40.
Effects of edaphic factors (salinity, pH, Na+, K+, Ca++, CaCO3, water holding capacity, and grain size) on the spatial distribution of plants were investigated. Soil was sampled at 22 stands. Sixteen plant species were recorded from these stands. Relation between edaphic factors and plant distribution was investigated using correlation statistical analysis. Distribution of some plants was found to be highly correlated with edaphic factor(s). 相似文献