Richness and structure of plant communities in temporary pools from western Morocco: influence of human activities

Temporary pools are numerous in coastal plains of Atlantic Morocco and have a rich and diverse flora. These habitats are increasingly under pressure by man impact through grazing by domestic livestock and the development of annual crops in their catchments. The objectives of this work were to evaluate the species richness and the species composition of the vegetation of a sample of 30 pools in this region, in order to assess the structure of the vegetation within pools and to evaluate the role of environmental and anthropogenic factors in their richness and species composition. The results highlighted the species richness of the pools with 300 species found among which annual species were heavily dominant. The structure of the vegetation varied within pools according to a topographical/flooding gradient and between pools in relation with the land use in the surrounding areas. Three vegetation belts were recognized from the centre to the periphery of the pool. The total species richness per pool was not found significantly related to environmental or anthropogenic factors. The species characteristics of the pools were found mostly in the centre and their number affected by hydrological factors and land use in the pool and in the surrounding areas. The species characteristics of woodland habitats and of agriculture crops were found mostly in the peripheral zone. Temporary pools maintain specific communities of both aquatic and amphibious species, probably because of the selection induced by water level variations. The peripheral zone, although often dominated by terrestrial species, is clearly interpreted as part of the pool. It contains amphibious species highly characteristic of the pool for which the irregular flooding is a key environmental factor which decreases competition.     

Identification of a potential bottleneck in branched chain fatty acid incorporation into triacylglycerol for lipid biosynthesis in agronomic plants

In plant, unusual fatty acids are produced by a limited number of species. The industrial benefits of these unusual structures have led several groups to study their production in transgenic plants. Their research results led to very modest accumulation in seeds which was largely due to a limited knowledge of the lipid metabolism and fatty acid transfer in plants. More specifically we need to better understand the substrate specificity and selectivity of acyltransferases which are required for the incorporation of these unusual fatty acids into storage triacylglycerols. In our studies we have compared the incorporation of [¹⁴C] Oleoyl-CoA and Branched Chain Acyls-CoA into [³H] LPA-C18:1 by the Lysophosphatidic acid Acyltransferase (LPAAT) from developing seeds of agronomic plants (flax (Linum usitatissimum) and rape (Brassica napus)) and from a plant capable of producing high amounts of hydroxy fatty acids (castor bean (Ricinus communis)). Our assays demonstrate that LPAATs of the three studied species (1) incorporated preferentially oleyl-CoA, (2) could incorporate cyclopropane acyl-CoA when added alone as a substrate, however very weakly for rapeseed and castor bean seeds, (3) presented a low capacity to incorporate methyl branched acyl-CoA when added alone as a substrate (4) weakly incorporated cyclopropane acyl-CoA and was unable to incorporate methyl branched acyl-CoA when presented with an equimolar mix of oleyl-CoA and branched chain acyl-CoA. In all cases, the LPAAT had a low affinity for branched chain acyl-CoAs. The results show that LPAAT activity from agronomic plants constitutes a bottleneck for the incorporation of branched Chain acyl-CoA into PA.     

The ponA gene of Enterococcus faecalis JH2-2 codes for a low-affinity class A penicillin-binding protein

A soluble derivative of the Enterococcus faecalis JH2-2 class A PBP1 (*PBP1) was overproduced and purified. It exhibited a glycosyltransferase activity on the Escherichia coli 14C-labeled lipid II precursor. As a DD- peptidase, it could hydrolyze thiolester substrates with efficiencies similar to those of other class A penicillin-binding proteins (PBPs) and bind beta-lactams, but with k2/K (a parameter accounting for the acylation step efficiency) values characteristic of penicillin-resistant PBPs.     

Experimental study of the effect of hydrology and mechanical soil disturbance on plant communities in Mediterranean temporary pools in Western Morocco

Physical soil disturbance and the hydrology of temporary pools affect the biomass, species composition and richness of plant communities. Disturbance liberates sites for the random recruitment of new individuals. The addition of seeds modifies the structure of the communities. In order to verify these hypotheses concerning the vegetation of temporary pools, an experiment was carried out using 72 soil samples collected from a pool in Western Morocco and placed in containers. Three types of laboratory treatments were applied, each combined with control treatments: soil disturbance (control/disturbed), hydrology (flooded, saturated and dry) and seed addition (sowing/no sowing). The total biomass, the annual and perennial species richness were calculated for each sample to test the effects of disturbance, hydrology and seed addition on the biomass and species richness of the various plant communities. The results show that disturbance reduces the total biomass, especially of perennials, but without significantly increasing the richness of annuals. Seed addition does not affect the total biomass and reduces total richness only in saturated soil, where biomass production is high. The most extreme stress conditions (drought and flooding) limit the abundance of species and therefore competition. Guest editors: B. Oertli, R. Cereghino, A. Hull & R. Miracle Pond Conservation: From Science to Practice. 3rd Conference of the European Pond Conservation Network, Valencia, Spain, 14–16 May 2008