Glutamine synthetase and glutamate dehydrogenase contribute differentially to proline accumulation in leaves of wheat (Triticum aestivum) seedlings exposed to different salinity.

To investigate the roles of ammonium-assimilating enzymes in proline synthesis under salinity stress, the activities of glutamine synthetase (GS; EC 6.3.1.2) and NADH-dependent glutamate dehydrogenase (NADH-GDH; EC 1.4.1.2) were determined in leaves of wheat (Triticum aestivum) seedlings exposed to salt stress at 150 and 300 mM NaCl for 5d. At the lower salinity, only GS activity increased markedly. At 300 mM NaCl, however, NADH-GDH activity increased while GS activity decreased. A significant accumulation of proline was found only at high-salinity exposure while glutamate, a proline precursor, increased dramatically under both low and high salinity. These data suggests that GS-catalysis might be the main glutamate synthesis pathway under low salinity. At 300 mM NaCl, glutamate seems to be preferentially produced through the process catalyzed by NADH-GDH. The increase of ammonium in salinity-stressed wheat seedlings might have resulted from increased photorespiration, which is responsible for the higher NADH-GDH activity. The activity of Delta(1)-pyrroline-5-carboxylate reductase (P5CR; EC 1.5.1.2) was significantly enhanced at 300 mM NaCl but remained unchanged at 150 mM. Delta(1)-Pyrroline-5-carboxylate synthetase (P5CS) activity did not show a specific response, indicating that P5CR might be the limiting step in proline synthesis from glutamate at high salinity.

Construction of a stable expression vector for Leifsonia xyli subsp. cynodontis and its application in studying the effect of the bacterium as an endophytic bacterium in rice.

To study the possibility of utilizing genetically engineered Leifsonia xyli subsp. cynodontis (Lxc) as an endophytic bacterium in rice, we constructed an Escherichia coli-Lxc shuttle vector, pLGUS, containing a beta-glucuronidase reporter gene, which was stable both in vitro and in vivo. Lxc grows and expresses the beta-glucuronidase reporter gene in all parts of rice, except for seed. A 2-year field study using three rice varieties from China showed that Lxc inoculation did not have a negative effect on the growth and yield of any of these varieties. Therefore, Lxc has the potential to be used as a benign endophyte for the expression of foreign genes in rice.

Visual DNA microarrays for simultaneous detection of Ureaplasma urealyticum and Chlamydia trachomatis coupled with multiplex asymmetrical PCR.

Visual DNA microarrays, based on gold label silver stain (GLSS) and coupled with multiplex asymmetrical PCR, were developed for simultaneous, sensitive and specific detection of Ureaplasma urealyticum and Chlamydia trachomatis. 5'-end-amino-modified oligonucleotides, which were immobilized on glass surface, acted as capturing probes that were designed to bind complementary biotinylated targets DNA. The gold-conjugated streptavidins were introduced to the microarray for specific binding to biotin. The black image of microarray spots, resulting from the precipitation of silver onto nanogold particles bound to streptavidins, were used to detect biotinylated targets DNA visually or with a visible light scanner. Multiplex asymmetrical PCR of U. urealyticum, C. trachomatis and Bacillus subtilis (used as positive control) was performed to prepare abundant biotinylated single-stranded targets DNA, which affected detection efficiency and sensitivity of hybridization on microarray. Plenty of clinical samples of U. urealyticum and C. trachomatis from infected patients were tested using home-made DNA microarrays. For its high sensitivity, good specificity, simplicity, cheapness and speed, the present visual gene-detecting technique has potential applications in clinical fields.

Purification and Studies of Some Properties of Pig-kidney Biliverdin Reductase.

Biliverdin reducatase was purified from pig-kidney to homogeneous form through DEAE 52-cellulose, Sephadex G-100 and Procion red HE 3B-Sepharose 4B column chromatography, The enzyme was estimated to be a monomer with a molecular weight of 66kD by SDS-PAGE. A gel staining in basic-pyridine solution of heme was used to identify purified biliverdin reductase. The enzyme utilized NADPH and NADH as electron donors for the reduction of biliverdin to produce bilirubin. The apparent K(m) values for biliverdin were established to be 1.25 &mgr;M with NADPH and 2.52 &mgr;M with NADH.