Documents found
-
512.
-
516.More information
Most of the works achieved so far in semi-arid lakes have been focused especially on the dynamics, structure and metabolic of phytoplankton. However, this issue has not been addressed in term of metabolic microphytobenthic cells activity. With an aim increasing the relative scientific knowledge relating to the functioning of lacustrian ecosystems in the Maghreb for which the data are still very fragmentary, special attention has been granted to the study of the microphytobenthos metabolism, by means of determining essential cellular constituents (carbohydrates, proteins and lipids) of the reservoir Allal El Fassi.The Allal El Fassi reservoir is about 47 km of Fez. It was built in 1992, and is 7 km long, 0.7 km wide and 34 m maximum depth. The reservoir is classed as mesotrophic and used for irrigation, recreation and to supply drinking water.The study was conducted between August 1996 and July 1997. Samples were taken vertically from the deepest point of the reservoir by means of a Van-Dorn sampler from seven depths: Near the surface, - 2 m, - 5 m, - 10 m, - 15 m, - 20 m and close to the bottom. The samples were analysed for physical, chemical and metabolism of Diatom. Analysis of Nitrogen and phosphate was done following Golterman method and oxygen dissolved by the Winkler method.Given the advantage that presents the artificial substrata (polyethylene leaves) for sample of periphyton, we have opted for the utilization of these substrata similar to these already used by WATANABE et al. (1988). These substrata are submerged during four weeks at different depths.The evaluation of the microphytobenthic biomass has been carried out according to the method of LOHMAN (1908) after enumerations to the microscope Olympus following the technique of LECLERCQ (1984).The dosage of the carbohydrates has been undertaken according to the method of MOAL et al. (1985), while concentrations of proteins have been determined according to the method of LOWRY (1951) and lipids have been extracted according to the method chloroform/methanol.The results show that microphytobenthic biomass presents important fluctuations since extreme values are respectively 0.25·104 µg·cm-2 and 14.95·104 µg·cm-z.Carbohydrates and lipids concentrations (mean=4.52 µg·cm-z and 2.27 µg·cm-z, respectively) are clearly less high than those of proteins (mean=81.84 µg·cm-2). This result indicates that the metabolism of the microphytobenthos of the Allal El Fassi reservoir is oriented towards the preferential protein synthesis. The vertical distribution of proteins, carbohydrates and lipids concentrations shows a well marked stratification, maximal concentrations generally recorded between 0 and 5 m. These high concentrations are attributed to the development of Niztchia, Navicula, Cymbella, Cyclotella, Melosira and Cocconeis.Proteins and carbohydrates concentrations were significantly correlated (r=0.84, p=0.01 at 0m and r=0.52, p=0.10 at 5 m). On the opposite, concentrations of lipids have no correlation neither with those of proteins, nor with those of the carbohydrates.The correlation between the lipids concentrations and the microphytobenthic biomass, is highly significant (r=0.48, p=0.10). This correlation results notably into the fact that lipids visualise well the evolution of the microphytobenthic biomass. However, no significant correlation was found between proteins, carbohydrates concentrations and biomass microphytobenthic.Many works prove the influences of some environmental factors namely light intensity and the temperature on the biochemical composition of the microphytobenthic. In this way, we observe that in period of high temperature, the synthesis of lipids is important. The positive correlation between temperature and lipids (r=0.48, p=0.10) support the observed increase in the concentrations of this variable with increasing temperature. Nevertheless, no significant correlation was found between proteins and carbohydrates concentrations and temperature, which suggests that the synthesis of these components is made independently from this factor. Oxygen dissolved and nitrogen intervene equally in the synthesis of lipids.
Keywords: Réservoir, microphytobenthos, lipides, protéines, glucides, Reservoir, microphytobenthic, carbohydrates, proteins, lipids
-
518.More information
Surveys on viruses associated with Barley Yellow Dwarf (BYD) and their vectors were carried out in Algerian cereal areas (Guelma, Constantine, Algiers, Sidi-belabes, Adrar) in 1997 and 1998. Rhopalosiphum padi was present in all zones of culture, whereas R. maidis, Sitobion avenae, S. fragariae and Schizaphis graminum had only local distributions. In most areas BYD-like symptoms, i.e. dwarfing and yellowing of barley (Hordeum vulgare), dwarfing and reddening of oat (Avena sativa) and wheat (Triticum aestivum), were observed. Serological tests were done on these crops using DAS-ELISA (RMV and SGV) or TAS-ELISA using monoclonal antibodies specifie to CYDV-RPV or using different variant specifie BYDV-PAV (CpA and CpB) and BYDV-MAV monoclonal antibodies. BYDV-PAV was prevalent and few plant samples carrying RMV, SGV, BYDV-MAV or CYDV-RPV were detected. The relative frequencies of BYDV-PAV CpA and CpB serotypes were variable depending on the area and the crop season. The range of symptoms induced on barley by both Algerian BYDV-PAV CpB and BYDV-PAV CpA serotypes was mild to severe. Twenty-one BYDV-MAV isolates were compared using monoclonal antibodies, which distinguish two serotypes of this virus. Only one serotype was detected. This same serotype is also the most prevalent in Europe.
-
520.