M.T. Ruiz

High throughput virus‐induced gene silencing implicates heat shock protein 90 in plant disease resistance

Virus‐induced gene silencing was used to assess the function of random Nicotiana benthamiana cDNAs in disease resistance. Out of 4992 cDNAs tested from a normalized library, there were 79 that suppressed a hypersensitive response (HR) associated with Pto‐mediated resistance against Pseudomonas syringae. However, only six of these clones blocked the Pto‐mediated suppression of P.syringae growth. The three clones giving the strongest loss of Pto resistance had inserts corresponding to HSP90 and also caused loss of Rx‐mediated resistance against potato virus X and N‐mediated tobacco mosaic virus resistance. The role of HSP90 as a cofactor of disease resistance is associated with stabilization of Rx protein levels and could be accounted for in part by SGT1 and other cofactors of disease resistance acting as co‐chaperones. This approach illustrates the potential benefits and limitations of RNA silencing in forward screens of gene function in plants.

In Defense against Pathogens. Both Plant Sentinels and Foot Soldiers Need to Know the Enemy

Plants are major targets of microbes seeking a source of nutrition. A complex array of interactions between plants and microbes has evolved that reflects both the nutrient acquisition strategies of microbes and defense strategies of plants. Part of plant defense strategy includes an active offense

An EXCEL template for calculation of enzyme kinetic parameters by non-linear regression.

MOTIVATION An EXCEL template has been developed for the calculation of enzyme kinetic parameters by non-linear regression techniques. The tool is accurate, inexpensive, as well as easy to use and modify. AVAILABILITY The program is available from http://www.ebi.ac.uk/biocat/biocat.html CONTACT agustin. hernandez@bio.kuleuven.ac.be

Microstructure of laser floating zone (LFZ) textured (Bi, Pb)SrCaCuO superconductor composites

Abstract Directionally solidified high temperature superconducting (Bi, Pb)SrCaCuO pure ceramics and composites were obtained using a laser floating zone (LFZ) apparatus. The presence of secondary non-superconducting and metallic phases as well as their solidification habit have been analysed. The influence of the LFZ growth conditions and the precursor composition on the microstructure of the final products was studied using optical and electron microscopies.

Solution-based synthesis routes to (Bi 1− x Pb x ) 2 Sr 2 Ca 2 Cu 3 O 10+δ

A comparison of several solution syntheses with a solid-state route to the leadcontaining high Tc phase of the Bi-Sr-Ca-Cu-O system has been performed using DSC, TGA, X-ray diffraction, electron microscopy, magnetic ac susceptibility, and critical-current measurements. A novel polymer solution synthesis route is shown to yield an increased percentage of the 2223 high Tc phase when sintering is performed at the low temperature end of this phases stability range. Under the best preparative conditions given in the literature, however, the properties of samples obtained with the different synthetic methods described in the present study are shown to be similar. Samples derived from solution syntheses have been found to contain higher amounts of carbon precipitates, while samples derived from conventional solid-state synthesis contain CuO precipitates, according to energy dispersive spectroscopy analyses.

Characterization of multiple SPS knockout mutants reveals redundant functions of the four Arabidopsis sucrose phosphate synthase isoforms in plant viability, and strongly indicates that enhanced respiration and accelerated starch turnover can alleviate the blockage of sucrose biosynthesis.

We characterized multiple knock-out mutants of the four Arabidopsis sucrose phosphate synthase (SPSA1, SPSA2, SPSB and SPSC) isoforms. Despite their reduced SPS activity, spsa1/spsa2, spsa1/spsb, spsa2/spsb, spsa2/spsc, spsb/spsc, spsa1/spsa2/spsb and spsa2/spsb/spsc mutants displayed wild type (WT) vegetative and reproductive morphology, and showed WT photosynthetic capacity and respiration. In contrast, growth of rosettes, flowers and siliques of the spsa1/spsc and spsa1/spsa2/spsc mutants was reduced compared with WT plants. Furthermore, these plants displayed a high dark respiration phenotype. spsa1/spsb/spsc and spsa1/spsa2/spsb/spsc seeds poorly germinated and produced aberrant and sterile plants. Leaves of all viable sps mutants, except spsa1/spsc and spsa1/spsa2/spsc, accumulated WT levels of nonstructural carbohydrates. spsa1/spsc leaves possessed high levels of metabolic intermediates and activities of enzymes of the glycolytic and tricarboxylic acid cycle pathways, and accumulated high levels of metabolic intermediates of the nocturnal starch-to-sucrose conversion process, even under continuous light conditions. Results presented in this work show that SPS is essential for plant viability, reveal redundant functions of the four SPS isoforms in processes that are important for plant growth and nonstructural carbohydrate metabolism, and strongly indicate that accelerated starch turnover and enhanced respiration can alleviate the blockage of sucrose biosynthesis in spsa1/spsc leaves.

Fabrication of Ag/(Bi,Pb)SrCaCuO superconducting tapes☆

Abstract Ag-sheathed Bi-2223 mono- and multifilamentary superconducting tapes have been obtained from wires produced by the powder-in-tube method. The tapes have been characterized by scanning electron and polarized optical microscopy, together with critical current density ( J c and J c ( B )) measurements. A systematic study of the processing parameters (annealing time and temperature, compaction pressure and number of cycles) has led to an optimized procedure for the fabrication of high J c monofilamentary (2.1 × 10 4 A cm −2 at 77 K and zero field) tapes. Multifilamentary tapes have also been obtained with J c as high as 1.35 × 10 4 A cm −2 at 77 K and zero field.

Posttranslational regulation of nitrogenase activity by fixed nitrogen in Azotobacter chroococcum

Using anti-(Fe protein) antibody raised against the Fe protein of the photosynthetic bacterium Rhodospirillum rubrum, it was found that the Fe protein component of nitrogenase (EC 1.18.2.1) from Azotobacter chroococcum cells subjected to an ammonium shock, and hence with an inactive nitrogenase, appeared as a doublet in Western blot analysis of cell extracts. The Fe protein incorporated [32P]phosphate and [3H]adenine in response to ammonium treatment, and L-methionine-DL-sulfoximine, an inhibitor of glutamine synthetase (L-glutamate: ammonia ligase (ADP forming), EC 6.3.1.2), prevented Fe protein from inhibition and radioisotope labelling. These results support that A. chroococcum Fe protein is most likely ADP-ribosylated in response to ammonium. After ammonium treatment, when in vivo activity was completely inhibited, Fe-protein modification was still increasing. This suggests the existence of another mechanism of nitrogenase inhibition faster than Fe-protein modification. When ammonium was intracellularly generated instead of being externally added, as occurs with the short-term nitrate inhibition of nitrogenase activity observed in A. chroococcum cells simultaneously fixing molecular nitrogen and assimilating nitrate, a covalent modification of the Fe protein was likewise demonstrated.

The Azotobacter chroococcum nitrate permease is a multicomponent system

Abstract Nitrate uptake by Azotobacter chroococcum ATCC 4412 was sensitive to osmotic shock. Cytoplasmic membrane preparations from nitrate-grown cells exhibited three polypeptide components of 52, 49 and 44 kDa, respectively, that were missing from, or very much decreased in, N 2 -fixing or ammonium-grown cells. The A. chroococcum TR1 strain, which is deficient in nitrate uptake but exhibits normal levels of nitrate reductase (EC 1.6.6.1) and nitrite reductase (EC 1.6.6.4), lacked the 44 kDa membrane-bound protein while exhibiting the other two polypeptide components. Transfer of ammonium-grown A. chroococcum cells to a medium containing nitrate as the sole nitrogen source and [ 35 S]methionine resulted in parallel development of nitrate uptake activity and the above mentioned 52, 49, and 44 kDa polypeptides radioactively labelled. A. chroococcum MCD1, a pleiotropic mutant unable to use nitrate as a nitrogen source, had none of the membrane proteins inducible by nitrate in the wild-type cells. The results strongly suggest that a multicomponent system transports nitrate in A. chroococcum .

Magnetic and electric transport properties of Ag/(Bi,Pb)SrCaCuO superconducting fibres

Abstract Novel-textured Ag/(Bi,Pb)-SrCaCuO composite fibres have been grown by the laser floating zone method. Important parameters that have been studied include growing speed, silver content and post-annealing conditions. Polarized optical and scanning electron microscopy, a.c. and d.c. magnetic measurements and d.c. electric transport current have been used to characterize the final products. Silver addition has two main effects: it considerably improves the degree of texture within the fibre, and it lowers the melting point of the material. Moderate critical currents ( J c (77 K) ≈ 100 A cm −2 ) have been obtained with agreement between transport and inductive values.