RESUMEN
We present results of an experiment performed in Lake Baikal at a depth of approximately 1 km. The photomultipliers of an underwater neutrino telescope under construction at this site were illuminated by a distant laser. The experiment not only provided a useful cross-check of the time calibration of the detector but also allowed us to determine inherent optical parameters of the water in a way that was complementary to standard methods. In 1997 we measured an absorption length of 22 m and an asymptotic attenuation length of 18 m. The effective scattering length was measured as 480 m. By use of (cos theta) = 0.95 (0.90) for the average scattering angle, this length corresponds to a geometric scattering length of 24 (48) m.
RESUMEN
Accumulation of free proline (Pro) by bacteria and plants serves as a mechanism protecting these organisms from abiotic stress. We introduced two E. coli genes, proBosm, encoding a mutant variant of the first enzyme of the Pro biosynthetic pathway, gamma-glutamyl kinase, and proA, encoding the second enzyme of the Pro pathway, glutamyl-gamma-semialdehyde dehydrogenase, into tobacco plants. The spontaneous proBosm mutation was selected for Pro overproduction and mapped to the N-terminus of a polypeptide chain; it was found to result from one amino-acid substitution. Two E. coli genes were simultaneously introduced into tobacco plants, each under the control of a strong constitutive CaMV 35S promoter, which contained a duplicated sequence of enhancer, or the root-specific Pmas promoter sequence. Transgenic plants were characterized by Pro overproduction, increased resistance to L-azetidine-2-carboxylic acid (a toxic analog of Pro), and tolerance to salt stress.
Asunto(s)
Regulación de la Expresión Génica de las Plantas , Técnicas de Transferencia de Gen , Genes Bacterianos , Nicotiana/genética , Plantas Tóxicas , Prolina/biosíntesis , Regiones Promotoras Genéticas , Agrobacterium tumefaciens/genética , Aldehído Oxidorreductasas/genética , Escherichia coli/genética , Vectores Genéticos , Glutamato-5-Semialdehído Deshidrogenasa , Fosfotransferasas (aceptor de Grupo Carboxilo)/genética , Plantas Modificadas Genéticamente , Plásmidos , Nicotiana/metabolismo , Transformación GenéticaRESUMEN
The proB proA operons (which are blocked by the feedback inhibition of proline production) of Escherichia coli wild type or with the mutation proBosm, blocking feedback inhibition effect of proline production, were cloned in a broad host range shuttle vector pVA 12-2. The hybrid plasmids pLVA(proB+A+) and pNSA(proBosm proA), were transferred into a low level osmotolerance Rhizobium fredii strain BD32. Both types of transconjugants were characterised by increased osmotolerance in a minimal medium supplied with 0.4-0.8 M NaCl but in the case of pNSA the effect was more significant. The strain BD32/pNSA had an increased level of intracellular proline concentration. Practical application of the increase in Rhizobium resistance to the stress factors is discussed.
Asunto(s)
Aldehído Oxidorreductasas/genética , Fosfotransferasas (aceptor de Grupo Carboxilo)/genética , Rhizobium/genética , Equilibrio Hidroelectrolítico , Clonación Molecular , Escherichia coli/genética , Genes Bacterianos , Prueba de Complementación Genética , Glutamato-5-Semialdehído Deshidrogenasa , Operón , Prolina/fisiología , Glycine maxRESUMEN
Effects of recombinant bacteria Rhizobium fredii/pNSA, content of proBosm proA operon, and R.fredii/pLVA, content of proBA wild type operon, on soybean plants were studied. R.fredii BD32/pNSA were found to synthesize more proline and to express higher osmotolerance than R.fredii BD32/pLVA or wild type bacteria. Plants infected with R.fredii Bd32/pNSA were characterized by lower water consumption before blooming. Moreover, these bacteria were found to promote more rapid sprout of seeds under unfavorable climatic conditions.