Descripción: In plant sexual reproduction, water and solute movement are tightly regulated, suggesting the involvement of aquaporins. We previously identified TIP5;1 and TIP1;3 as the only Arabidopsis aquaporin genes that are selectively and highly expressed in mature pollen, and showed that they can transport both water and urea when expressed in Xenopus oocytes. Here, we show that TIP5;1 has unusual characteristics, as its water transport activity is regulated by pH. Analysis of the water transport activity of a mutant version of TIP5;1 (TIP5;1-H131A) and amino acid alignment with other plant aquaporins regulated by pH suggested that a conserved motif is involved in pH sensing. GFP-TIP5;1 is located in the mitochondria of pollen tubes. The single mutants tip1;3 and tip5;1, as well as the tip1;3 tip5;1 double mutant, are fertile, but all mutants had shorter than normal pollen tubes when germinated in vitro in the absence of exogenous nitrogen. Thus, we propose that TIP5;1 and TIP1;3 are involved in nitrogen recycling in pollen tubes of Arabidopsis thaliana. © 2010 The Authors. The Plant Journal © 2010 Blackwell Publishing Ltd.

Descripción: Sinorhizobium meliloti is a symbiotic nitrogen-fixing bacterium that elicits nodule formation on roots of alfalfa plants. S. meliloti produces two exopolysaccharides (EPSs), termed EPS I and EPS II, that are both able to promote symbiosis. EPS I and EPS II are secreted in two major fractions that reflect differing degrees of subunit polymerization, designated high- and low-molecularweight fractions. We reported previously that EPSs are crucial for autoaggregation and biofilm formation in S. meliloti reference strains and isogenic mutants. However, the previous observations were obtained by use of "domesticated" laboratory strains, with mutations resulting from successive passages under unnatural conditions, as has been documented for reference strain Rm1021. In the present study, we analyzed the autoaggregation and biofilm formation abilities of native S. meliloti strains isolated from root nodules of alfalfa plants grown in four regions of Argentina. 16S rRNA gene analysis of all the native isolates revealed a high degree of identity with reference S. meliloti strains. PCR analysis of the expR gene of all the isolates showed that, as in the case of reference strain Rm8530, this gene is not interrupted by an insertion sequence (IS) element. A positive correlation was found between autoaggregation and biofilm formation abilities in these rhizobia, indicating that both processes depend on the same physical adhesive forces. Extracellular complementation experiments using mutants of the native strains showed that autoaggregation was dependent on EPS II production. Our results indicate that a functional EPS II synthetic pathway and its proper regulation are essential for cell-cell interactions and surface attachment of S. meliloti. © 2012, American Society for Microbiology.

Descripción: A psychrotolerant marine bacterial strain, designated JUB59 T, was isolated from Antarctic surface seawater and classified as a new species of the genus Bizionia. Here, we present the first draft genome sequence for this genus, which suggests interesting features such as UV resistance, hydrolytic exoenzymes, and nitrogen metabolism. © 2011, American Society for Microbiology.

Descripción: Nitrogen compounds like urea and melamine are known to be commonly used for milk adulteration resulting in undesired intoxication; a well-known example is the Chinese episode occurred in 2008. The development of a rapid, reliable and economic test is of relevance in order to improve adulterated milk identification. Cyclic voltammetry studies using an Au working electrode were performed on adulterated and non-adulterated milk samples from different independent manufacturers. Voltammetric data and their first derivative were subjected to functional principal component analysis (f-PCA) and correctly classified by the KNN classifier. The adulterated and non-adulterated milk samples showed significant differences. Best results of prediction were obtained with first derivative data. Detection limits in milk samples adulterated with 1% of its total nitrogen derived from melamine or urea were as low as 85.0 mg·L-1 and 121.4 mg·L-1, respectively. We present this method as a fast and robust screening method for milk adulteration analysis and prevention of food intoxication. © 2012 by the authors; licensee MDPI, Basel, Switzerland.