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11.
Alfalfa leaf senescence induced by drought stress: photosynthesis, hydrogen peroxide metabolism, lipid peroxidation and ethylene evolution 总被引:10,自引:0,他引:10
Exchange rates of CO2 and H2 O and metabolism of hydrogen peroxide have been measured in leaves of alfalfa ev. Aragón) under drought stress. The inhibitory effect of drought upon photosynthesis depended on the severity of the stress treatment. Leaf water potential (Ψleaf ) down to,-2.8 MPa reduced CO2 availability due to stomatal closure and inhibited the rate of photosynthesis. Leaf water potential lower than,-2.8 MPa directly affected CO2 fixation, although CO2 was not limiting. Transpiration was more affected by stornatal closure than photosynthesis, which led to am apparent improvement in WUE (water use efficiency). Alfalfa leaves with Ψleaf lower than,-2.0 MPa had an increased quantum requirement, probably due to the severe stress effect on photoenergetic reactions.
Ethylene evolution from alfalfa leaves increased when they were subjected to Ψleaf of,- 1.6 MPa. Under more severe stress, the leaves showed low or almost no ethylene production. In parallel with the increase in ethyiene production, alfalfa leaves exhibited an increased membrane lipid peroxidation index (maloridialdehyde content) and an increased peroxide content. Superoxide disinutase activity (SOD; EC 1.15.1.1) was not affected by drought stress. Catalase (EC 1.11.1.6) was inhibited at slight stress, but significantly increased at a Ψleaf of -2.0 MPa. Peroxidase (EC 1.11.1.7) was progressively inhibited as drought stress developed. The possible implication of reactive O2 intermediates in drought stress-induced senescence of alfalfa leaves is discussed in the light of the pattern of enzymatic scavenging systems. 相似文献
Ethylene evolution from alfalfa leaves increased when they were subjected to Ψ
12.
Carbon Metabolism Enzymes of Rhizobium meliloti Cultures and Bacteroids and Their Distribution within Alfalfa Nodules 总被引:2,自引:1,他引:1 下载免费PDF全文
Several carbon metabolism enzymes were measured in cultured cells and bacteroids of Rhizobium meliloti 102F51 and in alfalfa root nodule cytosol. The enzyme activity levels of the pentose phosphate pathway were much higher than those of the Embden-Meyerhof-Parnas or Entner-Doudoroff pathways in extracts of cultured cells. The pattern of enzyme activities in the bacteroids was different from that of cultured cells. 相似文献
13.
Internally seedborne microorganisms are those surviving common surface sterilization procedures. Such microbes often colonize the radicle surface of a germinating soybean (Glycine max) seed, introducing an undefined parameter into studies on attachment and infection by Bradyrhizobium japonicum. Bacterial isolates from surface-sterilized soybean seed, cv. Williams 82 and cv. Maverick, used in our studies, were identified as Agrobacterium radiobacter, Aeromonas sp., Bacillus spp., Chryseomonas luteola, Flavimonas oryzihabitans, and Sphingomonas paucimobilis. Growth of these microbes during seed germination was reduced by treating germinating seeds with 500 micrograms/mL penicillin G. The effects of this antibiotic on seedling development and on B. japonicum 2143 attachment, nodulation, and nitrogen fixation are reported here. Penicillin G treatment of seeds did not reduce seed germination or root tip growth, or affect seedling development. No differences in nodulation kinetics, nitrogen fixation onset or rates were observed. However, the number of B. japonicum attached to treated intact seedlings was enhanced 200-325%, demonstrating that other root-colonizing bacteria can interfere with rhizobial attachment. Penicillin G treatment of soybean seedlings can be used to reduce the root colonizing microbes, which introduce an undefined parameter into studies of attachment of B. japonicum to the soybean root, without affecting plant development. 相似文献
14.
The exact mechanism(s) of infection and symbiotic development between rhizobia and legumes is not yet known, but changes
in rhizobial exopolysaccharides (EPSs) affect both infection and nodule development of the legume host. Early events in the
symbiotic process between Bradyrhizobium japonicum and soybean (Glycinemax [L.] Merr.) were studied using two mutants, defective in soybean lectin (SBL) binding, which had been generated from B. japonicum 2143 (USDA 3I-1b-143 derivative) by Tn5 mutagenesis. In addition to their SBL-binding deficiency, these mutants produced
less EPS than the parental strain. The composition of EPS varied with the genotype and with the carbon source used for growth.
When grown on arabinose, gluconate, or mannitol, the wild-type parental strain, B. japonicum 2143, produced EPS typical of DNA homology group I Bradyrhizobium, designated EPS I. When grown on malate, strain 2143 produced a different EPS composed only of galactose and its acetylated
derivative and designated EPS II. Mutant 1252 produced EPS II when grown on arabinose or malate, but when grown on gluconate
or mannitol, mutant 1252 produced a different EPS comprised of glucose, galactose, xylose and glucuronic acid (1:5:1:1) and
designated EPS III. Mutant 1251, grown on any of these carbon sources, produced EPS III. The EPS of strain 2143 and mutant
1252 contained SBL-binding polysaccharide. The amount of the SBL-binding polysaccharide produced by mutant 1252 varied with
the carbon source used for growth. The capsular polysaccharide (CPS) produced by strain 2143 during growth on arabinose, gluconate
or mannitol, showed a high level of SBL binding, whereas CPS produced during growth of strain 2143 on malate showed a low
level of SBL binding. However, the change in EPS composition and SBL binding of strain 2143 grown on malate did not affect
the wild-type nodulation and nitrogen fixation phenotype of 2143. Mutant 1251, which produced EPS III, nodulated 2 d later
than parental strain 2143, but formed effective, nitrogen-fixing tap root nodules. Mutant 1252, which produced either EPS
II or III, however nodulated 5–6 d later and formed few and ineffective tap root nodules. Restoration of EPS I production
in mutant 1252 correlated with restored SBL binding, but not with wild-type nodulation and nitrogen fixation.
Received: 6 October 1999 / Accepted: 18 November 1999 相似文献
15.
A purification procedure is described for the components of Bacillus polymyxa nitrogenase. The procedure requires the removal of interfering mucopolysaccharides before the two nitrogenase proteins can be purified by the methods used with other nitrogenase components. The highest specific activities obtained were 2750 nmol C2H4 formed . min-1 . mg-1 MoFe protein and 2521 nmol C2H4 formed . min-1 . mg-1 Fe protein. The MoFe protein has a molecular weight of 215 000 and contains 2 molybdenum atoms, 33 iron atoms and 21 atoms of acid-labile sulfur per protein molecule. The Fe protein contains 3.2 iron atoms and 3.6 acid-labile sulfur atoms per molecule of 55 500 molecular weight. Each Fe protein binds two ATP molecules. The EPR spectra are similar to those of other nitrogenase proteins. MgATP changes the EPR of the Fe protein from a rhombic to an axial-type signal. 相似文献
16.
17.
18.
Acetoacetyl-CoA thiolase of Bradyrhizobium japonicum bacteroids: purification and properties 总被引:4,自引:0,他引:4
Acetoacetyl-CoA thiolase of Bradyrhizobium japonicum bacteroids has been purified greater than 130-fold. The enzyme has a molecular weight of 180,000 +/- 15,000 and consists of four identical subunits of 44,000 +/- 2,000. The enzyme was specific for acetoacetyl-CoA; ketodecanoyl-CoA did not serve as a substrate. Catalysis proceeds via a ping-pong mechanism. Iodoacetamide effectively inhibited the enzyme but acetoacetyl-CoA provided considerable protection against this compound. Magnesium was found to inhibit both the thiolysis reaction and the condensation reaction. Acetoacetyl-CoA thiolysis activity was not affected by potassium, ammonium, or several organic acids but was found to be inhibited by NADH. The inhibition by NADH may have an effect during the decline of the symbiosis. 相似文献
19.
Although aquaporins (AQPs) play important roles in transcellular water movement, their precise quantification and localization remains controversial. We investigated expression levels and localizations of AQP3 and AQP8 and their possible functions in the rat digestive system using real-time polymerase chain reactions, western blot analysis and immunohistochemistry. We investigated the expression levels and localizations of AQP3 and AQP8 in esophagus, forestomach, glandular stomach, duodenum, jejunum, ileum, proximal and distal colon, and liver. AQP3 was expressed in the basolateral membranes of stratified epithelia (esophagus and forestomach) and simple columnar epithelia (glandular stomach, ileum, and proximal and distal colon). Expression was particularly abundant in the esophagus, and proximal and distal colon. AQP8 was found in the subapical compartment of columnar epithelial cells of the jejunum, ileum, proximal colon and liver; the most intense staining occurred in the jejunum. Our results suggest that AQP3 and AQP8 play significant roles in intestinal function and/or fluid homeostasis and may be an important subject for future investigation of disorders that involve disruption of intestinal fluid homeostasis, such as inflammatory bowel disease and irritable bowel syndrome. 相似文献
20.
Total protein extract of Bradyrhizobium japonicum cultivated in HM media were resolved by 2-D PAGE using narrow range IPG strips. More than 1200 proteins were detected, of which nearly 500 proteins were analysed by MALDI-TOF and 310 spots were tentatively identified. The present study describes at the proteome level a significant number of metabolic pathways related to important cellular events in free-living B. japonicum. A comparative analysis of proteomes of free-living and nodule residing bacteria revealed major differences and similarities between the two states. Proteins related to fatty acid, nucleic acid and cell surface synthesis were significantly higher in cultured cells. Nitrogen metabolism was more pronounced in bacteroids whereas carbon metabolism was similar in both states. Relative percentage of proteins related to global functions like protein synthesis, maturation & degradation and membrane transporters were similar in both forms, however, different proteins provided these functions in the two states. 相似文献