The Physiology and Proteomics of Drought Tolerance in Maize: Early Stomatal Closure as a Cause of Lower Tolerance to Short-Term Dehydration?

Understanding the response of a crop to drought is the first step in the breeding of tolerant genotypes. In our study, two maize (Zea mays L.) genotypes with contrasting sensitivity to dehydration were subjected to moderate drought conditions. The subsequent analysis of their physiological parameters revealed a decreased stomatal conductance accompanied by a slighter decrease in the relative water content in the sensitive genotype. In contrast, the tolerant genotype maintained open stomata and active photosynthesis, even under dehydration conditions. Drought-induced changes in the leaf proteome were analyzed by two independent approaches, 2D gel electrophoresis and iTRAQ analysis, which provided compatible but only partially overlapping results. Drought caused the up-regulation of protective and stress-related proteins (mainly chaperones and dehydrins) in both genotypes. The differences in the levels of various detoxification proteins corresponded well with the observed changes in the activities of antioxidant enzymes. The number and levels of up-regulated protective proteins were generally lower in the sensitive genotype, implying a reduced level of proteosynthesis, which was also indicated by specific changes in the components of the translation machinery. Based on these results, we propose that the hypersensitive early stomatal closure in the sensitive genotype leads to the inhibition of photosynthesis and, subsequently, to a less efficient synthesis of the protective/detoxification proteins that are associated with drought tolerance

New broad-spectrum resistance to septoria tritici blotch derived from synthetic hexaploid wheat

Septoria tritici blotch (STB), caused by the ascomycete Mycosphaerella graminicola, is one of the most devastating foliar diseases of wheat. We screened five synthetic hexaploid wheats (SHs), 13 wheat varieties that represent the differential set of cultivars and two susceptible checks with a global set of 20 isolates and discovered exceptionally broad STB resistance in SHs. Subsequent development and analyses of recombinant inbred lines (RILs) from a cross between the SH M3 and the highly susceptible bread wheat cv. Kulm revealed two novel resistance loci on chromosomes 3D and 5A. The 3D resistance was expressed in the seedling and adult plant stages, and it controlled necrosis (N) and pycnidia (P) development as well as the latency periods of these parameters. This locus, which is closely linked to the microsatellite marker Xgwm494, was tentatively designated Stb16q and explained from 41 to 71% of the phenotypic variation at seedling stage and 28–31% in mature plants. The resistance locus on chromosome 5A was specifically expressed in the adult plant stage, associated with SSR marker Xhbg247, explained 12–32% of the variation in disease, was designated Stb17, and is the first unambiguously identified and named QTL for adult plant resistance to M. graminicola. Our results confirm that common wheat progenitors might be a rich source of new Stb resistance genes/QTLs that can be deployed in commercial breeding programs

Design of a basic angle monitoring system in Silicon Carbide

Due to the 10 microarcsecond accuracy, with which GAIA will measure the positions of stars using 2 astrometric telescopes, stability requirements on the payload module are extremely stringent. In order to achieve the required 10 microarcsecond accuracy, a metrology system could be installed on the satellite to monitor variations on the basic angle: the basic angle monitoring system. This system has high stability requirements of picometers in several hours and is therefore, like the rest of the payload module, constructed of Silicon Carbide. This is a ceramic material with good mechanical and thermal properties. However it also needs special attention in design, because final processing is difficult. The mounting of optical components is performed directly on the optical bench, by tensioning the optical components with spiders against the optical bench. Alignment is performed by shifting the component across a plane using an external and removable alignment mechanism. In the near future experiments will be performed to proof the design

Experimental set-up for testing alignments and measurement stability of a metrology system in Silicon Carbide for GAIA

The GAIA satellite will make a 3-D map of our Galaxy with measurement accuracy of 10 microarcseconds using two astrometric telescopes. The angle between the lines-of-sight of the two telescopes will be monitored using the Basic Angle Monitoring system with 1 microarcsecond accuracy. This system will be an interferometer consisting of a number of small mirrors and beam splitters in Silicon Carbide. Silicon Carbide has very high specific stiffness and very good thermal properties (low CTE and high conductivity). It also is a very stable material. A possible concept design for this Basic Angle Monitoring system is subject of a PhD study performed at the Technische Universiteit Eindhoven and TNO Science and Industry (The Netherlands). To prove that this concept design meets the alignment and measurement stability requirements, the GAIA extreme stability optical bench is developed. It will consist of a fourfold Michelson interferometer with four separate optical paths, which will measure the stability of the optical bench and the individual optical components. Also thermal cycling experiments and vibrations tests will be performed. ‘Absolute’ position measurements of the optical components with respect to the optical bench after the vibrations test will be performed using markers. The GAIA extreme stability optical bench will be placed in a vibration damped vacuum tank in order to imitate the highly stable L2 space environment. The goal is to obtain the first results early 2006