The stoichiometry of the chloroplast ATP synthase oligomer III in Chlamydomonas reinhardtii is not affected by the metabolic state

The chloroplast H⁺-ATP synthase is a key component for the energy supply of higher plants and green algae. An oligomer of identical protein subunits III is responsible for the conversion of an electrochemical proton gradient into rotational motion. It is highly controversial if the oligomer III stoichiometry is affected by the metabolic state of any organism. Here, the intact oligomer III of the ATP synthase from Chlamydomonas reinhardtii has been isolated for the first time. Due to the importance of the subunit III stoichiometry for energy conversion, a gradient gel system was established to distinguish oligomers with different stoichiometries. With this methodology, a possible alterability of the stoichiometry in respect to the metabolic state of the cells was examined. Several growth parameters, i.e., light intensity, pH value, carbon source, and CO₂ concentration, were varied to determine their effects on the stoichiometry. Contrary to previous suggestions for E. coli, the oligomer III of the chloroplast H⁺-ATP synthase always consists of a constant number of monomers over a wide range of metabolic states. Furthermore, mass spectrometry indicates that subunit III from C. reinhardtii is not modified posttranslationally. Data suggest a subunit III stoichiometry of the algae ATP synthase divergent from higher plants.     

Quantification of free and conjugated abscisic acid in five genotypes of barley (Hordeum vulgare L.) under water stress conditions

The goal of the present study was to obtain new insights into the mechanisms underlying drought stress adaptations in barley plants. For this purpose we evaluated changes in endogenous abscisic acid (ABA) and its glucose ester conjugate (ABAGE), as well as changes in proline content, water relations and growth parameters of five barley genotypes with different drought resistance characteristics. Different responses among the five genotypes studied (Ardahoui, Pakistan, Rihane, Manel ad Roho) led to changes in their pattern of growth and development under drought conditions. Water stress induced a reduction in relative water content, as well as an increase in proline content and endogenous ABA concentrations in all tested genotypes. The lack of water led to a 2-fold increase in proline content for var. Rihane and to a 5-fold increase in endogenous ABA for cv. Ardhaoui. Also, increases in endogenous ABAGE in all genotypes except for cv. Ardhaoui were observed. Our results show that changes in ABA and ABAGE correlated with variations in proline content and growth parameters of these genotypes which present different mechanisms to cope with water stress. We also suggest that new regulatory mechanisms implying ABA mobilization can be of great importance in adaptation of barley to drought.     

Structural identities of four glycosylated lipids in the oral bacterium Streptococcus mutans UA159

The cariogenic bacterium Streptococcus mutans is an important dental pathogen that forms biofilms on tooth surfaces, which provide a protective niche for the bacterium where it secretes organic acids leading to the demineralization of tooth enamel. Lipids, especially glycolipids are likely to be key components of these biofilm matrices. The UA159 strain of S. mutans was among the earliest microorganisms to have its genome sequenced. While the lipids of other S. mutans strains have been identified and characterized, lipid analyses of UA159 have been limited to a few studies on its fatty acids. Here we report the structures of the four major glycolipids from stationary-phase S. mutans UA159 cells grown in standing cultures. These were shown to be monoglucosyldiacylglycerol (MGDAG), diglucosyldiacylglycerol (DGDAG), diglucosylmonoacylglycerol (DGMAG) and, glycerophosphoryldiglucosyldiacylglycerol (GPDGDAG). The structures were determined by high performance thin-layer chromatography, mass spectrometry and nuclear magnetic resonance spectroscopy. The glycolipids were identified by accurate, high resolution, and tandem mass spectrometry. The identities of the sugar units in the glycolipids were determined by a novel and highly efficient NMR method. All sugars were shown to have α-glycosidic linkages and DGMAG was shown to be acylated in the sn-1 position by NMR. This is the first observation of unsubstituted DGMAG in any organism and the first mass spectrometry data for GPDGDAG.