Search results for "Clark"
showing 10 items of 59 documents
Histological and electron microscopical observations on the effects of lead on gills and midgut gland ofProcambarus clarkii
1991
Adult intermolt specimen of Procambarus clarkii (Crustacea, Decapoda) have been treated for 96 hours in aquaria with 100mg/l of lead. The gills and midgut gland were processed and studied in the electron microscope. The gill filament shows important changes in the ultrastructure of the epithelial cells and the cuticle. The hepatopancreatic cells studied (i.e. the vacuolated and dark cells) do not show noticeable structural changes but accumulate lead (electrondense precipitates) mainly in lysosomes.
Determination of lead in treated crayfish Procambarus clarkii: accumulation in different tissues.
1988
The continual loading of trace metals into our environment represents a water pollution problem due to their toxic effects on aquatic biota. In addition, metal ions can be incorporated into food chains and concentrated by aquatic organisms to a level that affects their physiological state. There are several investigations on the toxic effects and bioaccumulation of lead in fishes, molluscs, and crustaceans. Lake Albufera (Valencia, Spain) and the surrounding rice-field waters are subjected to large loads of sewage and toxic industrial residues (including heavy metals) from many urban wastewaters in the area. In 1978, the American red crayfish Procambarus clarkii (Girard) appeared in Lake Al…
Cadmium, mercury, and lead effects on gill tissue of freshwater crayfishProcambarus clarkii (girard)
1989
Intermolt adult crayfish P. clarkii were used for this work. After acclimatization to laboratory conditions crayfish were exposed to sublethal concentrations of cadmium, mercury, and lead for 96 h. Gills of control and exposed crayfish were removed and ATPase activity and oxygen uptake rate were determined. Structural damage of gill filaments was also observed. Gill tissue respiration rates were measured for individual crayfish using a Gilson differential respirometer. Lead causes a decrease of gill oxygen uptake, but neither cadmium nor mercury seems to affect it at the concentrations employed. Although all metals studied alter gill filament structure, lead damage is the most apparent. In …
Effects of cadmium on the biochemical composition of the freshwater crayfishProcambarus clarkii (Girard, 1852)
1991
Lake Albufera of Valencia (Spain) and the surrounding rice field waters are subjected to very heavy loads of sewage and toxic residues. Among these residues include heavy metals which have been deposited from the many urban and waste waters in this area. The American red crayfish, Procambarus clarkii from Albufera Lake has high resistance to heavy metals. The authors have also found that P. clarkii shows a high capacity for cadmium accumulation in experimental conditions and natural conditions since crayfish collected in this area contained considerable amounts of cadmium in several tissues even after 15 days of depuration in clean water. Since the physiological changes that take place when…
Enhanced levels of S-linalool by metabolic engineering of the terpenoid pathway in spike lavender leaves
2013
Transgenic Lavandula latifolia plants overexpressing the linalool synthase (LIS) gene from Clarkia breweri, encoding the LIS enzyme that catalyzes the synthesis of linalool were generated. Most of these plants increased significantly their linalool content as compared to controls, especially in the youngest leaves, where a linalool increase up to a 1000% was observed. The phenotype of increased linalool content observed in young leaves was maintained in those T1 progenies that inherit the LIS transgene, although this phenotype was less evident in the flower essential oil. Cross-pollination of transgenic spike lavender plants allowed the generation of double transgenic plants containing the …
Determination of mercury by cold‐vapour technique in several tissues of treated American red crayfish (Procambarus clarkii)
1988
Abstract Adult intermolt specimens of American red crayfish (Procambarus clarkii) collected from Lake Albufera (Valencia, Spain), were exposed to mercury during 96 h. The Hg‐concentrations used were 50, 100, and 250 μg Hg/1 as Cl2Hg. The content of mercury in muscle, midgut gland, antennal glands and gills was investigated. Determinations of mercury were made by cold‐vapour technique and AAS. The mercury levels in all examinated tissues increased significantly (ANOVA test, p < 0.01) with increasing Hg‐concentration in the water.
John M. Clark and frank H. Knight on the adding-up theorem, overhead costs, and more
2018
This note offers new archival insight into a 1925 polemical exchange between Frank Knight and John Maurice Clark that was hosted in the pages of Journal of Political Economy. Although the exchange centered on the effects of overhead costs on marginal productivity theory and the so-called adding-up theorem, it also provided significant elements to assess the methodological differences between two of the most representative American economists of the interwar years.
The activity of glutathione S-transferase in hepatopancreas of Procambarus clarkii: Seasonal variations and the influence of environmental pollutants
1991
Abstract 1. 1The glutathione S -transferase activity in hepatopancreas of the American red crayfish Procambarus clarkii after 15 days' acclimatization in tap water aquaria was measured in specimens collected monthly for a whole year, and shows seasonal variation. 2. 2. Previous data on the environmental pollution of Lake Albufera suggest a possible correlation with the activity tested in the different seasons of the year considering the results of non-acclimatized animals.
Cadmium induced metallothionein in hepatopancreas of Procambarus clarkii: Quantification by a silver-saturation method
1993
Abstract 1. Cadmium induced metallothionein (MT) in crayfish hepatopancreas was measured by silver-saturation method. 2. An increase in MT content was recorded in crayfish hepatopancreas after 12 hr of exposure to 10 mg Cd/l. 3. There was found to be a linear relationship between MT concentrations in hepatopancreas and cadmium concentration in the water. 4. MT levels in hepatopancreas of 20 mg Cd/l exposed crayfish were 7-fold higher than those in control animals.
The effect of time, concentration and temperature on bioaccumulation in the gill of crayfish procambarus clarkii induced by organochlorine pesticides…
1993
Abstract 1. Crayfish were exposed to 1 25 th 96-hr lc 50 and 96-hr lc 50 of lindane and endosulfan for 1, 24, 48, 72 and 96 hr. 2. Concentrations of lindane and endosulfan were determined in gill tissue at 22°C and 29°C. 3. Clear differences were found in all concentrations, times and temperatures tested in gill tissues. 4. The highest accumulation of pesticide was found in the lc 50 endosulfan value.