Cd Distribution in the Tissues of Oysters (Crassostrea Gigas) Exposed Chronically In Situ

This study was designed to monitor the evolution of the nature of Cd-binding molecular compounds in oysters transplanted from a low-contaminated area to a highly Cd-polluted site. These compounds have been compared to those found in oysters from the low-contaminated site, used as control, and from the native molluscs of the polluted area. We have also studied the influence of the length of exposure, collecting oysters after transplantation having been going on for 1 or 3 months. We have compared the quantities of Cd bound to soluble or insoluble compounds. The Cd distribution among cytosolic compounds was analyzed by gel permeation. Four classes of Cd-binding molecular compounds were separated and their relative significance in metal fixation was found to differ among resident and transplanted oysters.     

Die Entwicklung des Plazentastieles beim Meerschweinchen

As basis for detailed studies into the significance of the guinea pig subplacenta the formal development of the placental stalk which contains the subplacenta in its center was investigated in this species. Fifty conventional, domesticated, genetically undefined guinea pigs pregnant 8–63 days were used. The placentas were studied on semi-thin and paraffin sections on some of which morphometric observations were made. The findings provide the first three-dimensional picture of the subplacenta and give information of its development. The studies show that this region has neither a growth function nor a maternofetal transport function.     

Ultrastructural and Cytochemical Aspects of the Interaction Between the Mycoparasite Pythium oligandrum and Soilborne Plant Pathogens

ABSTRACT The interaction between the oomycete Pythium oligandrum and various soilborne oomycete and fungal plant pathogens (P. ultimum, P. aphanidermatum, Fusarium oxysporum f. sp. radicis-lycopersici, Verticillium albo-atrum, Rhizoctonia solani, and Phytophthora megasperma) was studied by light and electron microscopy in order to assess the relative contribution of mycoparasitism and antibiosis in the antagonistic process. Scanning electron microscope investigations of the interaction regions showed that structural alterations of all pathogenic fungi and oomycetes (except for Phytophthora megasperma) occurred soon after contact with the antagonist. Light and transmission electron microscope studies of the interaction region between the antagonist and P. ultimum revealed that intimate contact between both partners preceded a sequence of degradation events including aggregation of host cytoplasm and penetration of altered host hyphae. Localization of the host wall cellulose component showed that cellulose was altered at potential penetration sites. A similar scheme of events was observed during the interaction between P. oligandrum and F. oxysporum f. sp. radicis-lycopersici, with the exception that complete loss of host protoplasm was associated with antagonist invasion. The interaction between P. oligandrum and R. solani resulted in an abnormal deposition of a wall-like material at potential penetration sites for the antagonist. However, the antagonist displayed the ability to circumvent this barrier and penetrate host hyphae by locally altering the chitin component of the host hyphal wall. Interestingly, antagonist cells also showed extensive alteration as evidenced by the frequent occurrence of empty hyphal shells. In the case of Phytophthora megasperma, hyphal interactions did not occur, but hyphae of the plant pathogen were damaged severely. At least two distinct mechanisms appear to be involved in the process of oomycete and fungal attack by P. oligandrum: (i) mycoparasitism, mediated by intimate hyphal interactions, and (ii) antibiosis, with alteration of the host hyphae prior to contact with the antagonist. However, the possibility that the antagonistic process may rely on the dual action of antibiotics and hydrolytic enzymes is discussed.     

Food intake adjustments of chicks: Short term reactions to deficiencies in lysine,methionine and tryptophan

1. Two experiments were conducted to compare food intake responses of broiler chicks fed diets varying in lysine, methionine, and tryptophan. Diet D was formulated to create simultaneous deficiencies of lysine, methionine, and tryptophan. Diet A matched National Research Council (1984) recommendations for broilers, and diets B and C were, respectively, 2:1 and 1:2 mixes of diets A and D.

2. Short‐term food intake can provide information on the sequences of adaptation of chicks to a diet deficient in essential amino acids.

3. Chicks consumed 26% less of diet D than A during the first 24 h posthatch. When chicks fed diet A or D to 7 d of age were then fed one of 4 diets singly, within 24 h intake was lowest for chicks fed diet D. Within 48 h, food intake of diet C was more than that of diet D and less than that of diet A, while for diet B intake was more than of diet D but not different from diet A.

4. In the second experiment, chicks were fed diet A to 8 d and then diets A or D alone or given a choice of diets A and D from 8 to 20 d of age. Within 4 to 8 h, food intake of chicks fed diet D alone decreased markedly followed by partial recovery within 24 h. In a choice setting, consistent preference of Diet A over Diet D was observed within 7 h followed by stabilisation at about 65% diet A to 35% diet D.

5. Chicks fed diet D alone from 8 to 20 d of age, then placed in the same choice situation preferred diet A to D with a delay of less than one h and stabilisation at about 85%. Chicks provided a choice of diets A and D from 8 to 20 d, and then diet D alone reduced their food intake more quickly than those not given a choice initially.

6. Broiler chicks appear to react to amino acid deficiencies within a short period (hours) by adjusting their feed intake and/or selection. The response is influenced by age and prior experience.     

Seasonal dynamics of biomass production and herbage quality of three grasslands with contrasting functional compositions

Classifying grasses into plant functional types (PFT) according to their strategy of nutrient capture (PFT A, B and b) or nutrient conservation (PFT C) is claimed to predict variability in biomass production and herbage quality in grasslands. PFT A, B and b are characterized by higher production than PFT C, with higher nutritive value, which decreases rapidly. PFT C is characterized by lower nutritive value, which remains more stable in time. The aim of this study was to quantify the consequences of PFT composition at the community level on the seasonal dynamics of biomass and herbage quality for livestock feed. We studied three grasslands located in the same area with contrasting PFT composition and classified PFT A, PFT Bb and PFT C. The dynamics of vegetation stages, dry‐matter yield and nutritive value were followed over three vegetation cycles in 2007–2008. In the first cycle, biomass accumulation was high for the PFT A and PFT Bb grasslands and the high quality of herbage declined rapidly with the reproductive development. By contrast, biomass accumulation was slow in the PFT C grassland, with a lower quality that declined slowly, consistent with the later reproductive development. For regrowth cycles, the same ranking of grasslands was observed for biomass accumulation, and differences in digestibility were similar to those observed at the beginning of the first vegetation cycle. Combining type of grassland with sum of temperature for the first cycle and regrowth days for the second and third vegetation cycles provided quantitative models of herbage biomass and quality.     

Effects of storm Lothar (1999) on the chemical composition of soil solutions and on herbaceous cover,humus and soils (Fougères,France)

Examination of the effect of the 1999 storm on soil solution quality in an 81-year-old monitored plot in Fougères forest has not only made it possible to gain a better understanding of the impact of intensive silviculture in this ecosystem with low mineral fertility, but also to show that the cessation of internal recycling of chemical elements can be prevented by the presence of vegetation. The storm in December, 1999 resulted in several sudden openings in the forest cover, resulting in humus mineralization; the moder humus present before the storm was transformed rapidly into an oligomull. In the absence of any vegetation, the nitrates produced at the surface migrated down the profile by slow convective flux and the concentrations at depths of −10 and −30 cm increased during 2000. Herbaceous vegetation gradually replaced the arborescent strata present before the storm, taking-up the nitrate at the surface and thus limiting leaching into the deeper horizons. As convective transport is a slow process, the concentrations of nitrate in the soil solutions at depths of −55, −80 and −120 cm increased for about a year after the storm; then they decreased and stabilised in 2002. Nitrate leaching was accompanied by the migration of Al, Mg, K and Ca down the soil profile, depending on their relative availability. After the definitive installation of the herbaceous strata, the concentrations of elements in soil solutions returned to levels below those measured before the storm.