Phosphate Role in the Rhizobium-Legume Symbiosis- A Review

The international emphasis on maintaining farming systems productivity and sustainability is focusing on the use of renewable plant nutrients resources. In case of nitrogen (N), biological N2 fixation via symbiosis is the most important input for agricultural systems sustainability.  Research studying the association between rhizobia and the host legume plants has enhanced our knowledge and understanding of this symbiosis process. Our current knowledge establishes that any interruption in the flow of nutrients between symbionts affects this association.  Since phosphorus (P) is one of the essential nutrients in Rhizobium-legume symbiosis, and its limitation affects every aspect of the symbiosis, it is important to understand its function in the symbiosis process. This review will emphasis on the role of P in nodulation and in the functional symbiosis between rhizobia and legumes.

A Candida albicans early stage biofilm detachment event in rich medium

<p>Abstract</p> <p>Background</p> <p>Dispersal from <it>Candida albicans </it>biofilms that colonize catheters is implicated as a primary factor in the link between contaminated catheters and life threatening blood stream infections (BSI). Appropriate in vitro <it>C. albicans </it>biofilm models are needed to probe factors that induce detachment events.</p> <p>Results</p> <p>Using a flow through system to culture <it>C. albicans </it>biofilms we characterized a detachment process which culminates in dissociation of an entire early stage biofilm from a silicone elastomer surface. We analyzed the transcriptome response at time points that bracketed an abrupt transition in which a strong adhesive association with the surface is weakened in the initial stages of the process, and also compared batch and biofilm cultures at relevant time points. K means analysis of the time course array data revealed categories of genes with similar patterns of expression that were associated with adhesion, biofilm formation and glycoprotein biosynthesis. Compared to batch cultures the biofilm showed a pattern of expression of metabolic genes that was similar to the <it>C. albicans </it>response to hypoxia. However, the loss of strong adhesion was not obviously influenced by either the availability of oxygen in the medium or at the silicone elastomer surface. The detachment phenotype of mutant strains in which selected genes were either deleted or overexpressed was characterized. The microarray data indicated that changes associated with the detachment process were complex and, consistent with this assessment, we were unable to demonstrate that transcriptional regulation of any single gene was essential for loss of the strong adhesive association.</p> <p>Conclusion</p> <p>The massive dispersal of the early stage biofilm from a biomaterial surface that we observed is not orchestrated at the level of transcriptional regulation in an obvious manner, or is only regulated at this level by a small subpopulation of cells that mediate adhesion to the surface.</p

Effect of Salinity (NaCl) on Germination, Growth, Ion Accumulation, and Protein Synthesis in Alfalfa (Medicago Sativa L.)

To study the effect of NaCl stress on gene expression in alfalfa (Medicago sativa L.), greenhouse and laboratory experiments were conducted with 22 cultivars during germination and post-germination growth. The ability of alfalfa cultivars to germinate at the different NaCl concentrations was not related to their postgermination performance (salt tolerance) under those conditions. Genetic effects were evident for Na and Cl ion uptake and accumulation in alfalfa shoots and roots. The strategies of alfalfa cultivars to cope with NaCl stress includes exclusion of Na from shoots and Cl from roots or from the whole plant depending on cultivar and NaCl level. The reduction in shoot dry weight was not related to water stress or reduction in Ca, Mg, or chlorophyll concentrations. Results of this study indicated that the reduction in K ion uptake and more directly the toxic effects of high Na and Cl in plant tissues contributed to the reduction in shoot dry weight . The possible subpartitioning of Na and Cl ions between different tissues, cell types, cell components, and/or the different changes in protein structure and enzyme activity at the high Na and Cl concentrations, independent of total concentration of ions, might also contribute to differences in salt tolerance (shoot dry weight) among cultivars. The factors determining shoot dry weight in alfalfa grown under the different NaCl treatments of this study were not the same for all cultivars. Sodium chloride stress induced qualitative and quantitative changes in shoot and root proteins of alfalfa. These changes were dependent on cultivar and salt concentration, as well as length of exposure to salt stress