Carbohydrate Catabolism in Azospirillum amazonense

The nitrogen fixer Azospirillum amazonense grew on the various disaccharides, hexoses, and pentoses tested in this study but not on polyols and on some tricarboxylic acid cycle intermediates. An active transport system was detected for sucrose and glucose but not for mannitol and 2-ketoglutarate. Six A. amazonense strains were examined for 16 carbon-metabolizing enzymes, and the results indicate that these strains employ the Entner-Doudoroff pathway to catabolize sucrose, fructose, and glucose. The hexose monophosphate and Embden-Meyerhof-Parnas pathways were not detectable.     

Carbohydrate Accumulation Affects the Redox State of Ascorbate in Detached Tobacco Leaves

A decreased utilization of NADPH for CO₂ fixation as a result of carbohydrate accumulation in chlorotic leaves is generally believed to be associated with an increase in oxidative stress. Molecular oxygen may serve as an alternative electron acceptor of photosynthesis under these conditions. In order to test this hypothesis mature leaves of tobacco plants (Nicotiana tabacum) were detached, fed with glucose (50 mM) via the petiole, and used to study the effect of carbohydrate accumulation on the pigment content and the components of the superoxide dismutase-ascorbate-glutathione cycle. During a period of five days the concentration of total soluble carbohydrates increased substantially in leaves supplied with glucose in comparison with control leaves supplied only with water. This increase was accompanied by a twofold decrease in the chlorophyll content. In detached water-fed leaves the levels of most of the antioxidative components increased, whereas glucose feeding had no or only little additional effect on the activities of the protective enzymes, but caused a 1.6- and 4-fold increase in the contents of glutathione and ascorbate, respectively. In relation to the total foliar ascorbate pool, the amount of reduced ascorbate increased from about 30 % to 60 % upon feeding with glucose. These results do not support the idea that the accumulation carbohydrates per se cause an increased rate of superoxide production which necessitates increased activities of antioxidative enzymes. It rather appears that glucose-fed leaves have an increased reductive capacity that can be released via glutathione into the ascorbate pool, thereby, regulating the redox state of ascorbate.     

Breakdown of Galactolipids in Senescent Barly Leaves

The changes of galactolipids (MGDG and DGDG, largely 18:3/18:3), free fatty acids (FFA), and phosphatidylcholine (PC) taking place during senescence of primary barley leaves were analysed employing HPLC and GLC. Upon induction of senescence MGDG and, with some delay, DGDG began to disappear and were largely broken down at the end of the senescence period. A concomitant appearance of a pool of FFA could not be observed. However, PC accumulated during the main period of galactolipid breakdown. This change was due to the marked increase of the 18:3/18:3 molecular species of PC. An inverse correlation between the changes of galactolipids and PC could be established. A hypothesis featuring the conversion of galactolipids via diacylglycerol to PC is presented as the principal route of galactolipid breakdown.     

Carbohydrate Catabolism of Selected Strains in the Genus Agrobacterium

Radiorespirometric and enzyme analyses were used to reveal the glucose-catabolizing mechanisms functioning in single strains of seven presumed Agrobacterium species. The Entner-Doudoroff and pentose cycle pathways functioned in A. radiobacter, A. tumefaciens, A. rubi, and A. rhizogenes. Whereas both catabolic pathways were utilized to an almost equal degree in the A. radiobacter and A. tumefaciens strains, use of the Entner-Doudoroff pathway predominated in the A. rubi and A. rhizogenes strains. A stellulatum catabolized glucose almost solely through the Entner-Doudoroff pathway. In A. pseudotsugae and A. gypsophilae, glucose was metabolized mainly through the Emden-Meyerhof-Parnas pathway; the pentose phosphate pathway was also utilized.     

Chlorophyll Content and the Pattern of Yellowing in Senescent Leaves

In senescent leaves of four species, leaf chlorophyll contentwas approximately linearly related to the estimated area ofyellow tissue, but the species differed in the amount of chlorophylllost before yellowing became apparent. Cotoneaster and Vicia leaves and Sinapis cotyledons, which produceddistinct yellowing patterns lost about 40 per cent, whereasSolanumleaves, which yellowed more uniformly lost over 60 percent of the chlorophyll before yellowing was visible. It issuggested that the leaf-cell population of Solanum may senescerather more synchronously than the other species, and that chlorophyllloss before yellowing may be a useful index of synchrony ofsenescence in leaves.     

Pathways of Carbohydrate Metabolism in Microcyclus Species

Radiorespirometric and enzymatic studies were conducted to determine primary and secondary pathways of carbohydrate catabolism in Microcyclus aquaticus and M. flavus. M. aquaticus catabolizes both glucose and gluconate mainly via the Entner-Doudoroff and pentose phosphate pathways with some concurrent participation of the Embden-Meyerhof pathway. M. flavus, however, oxidizes glucose mainly via the Embden-Meyerhof pathway and gluconate via the Entner-Doudoroff pathway with some simultaneous operation of the pentose phosphate pathway. Both of the organisms showed evidence of the tricarboxylic acid cycle as a secondary pathway for the oxidation of carbohydrates.     

烟草叶片中呼吸电子传递途径在缓解叶绿体PSⅡ光抑制中的作用

前期研究发现线粒体交替氧化酶(AOX)呼吸途径对叶绿体光系统II(PSII)的光抑制有明显的缓解作用。线粒体内另一条呼吸途径——细胞色素氧化酶(COX)呼吸途径是否也具有光保护作用尚不清楚。该文通过荧光快速诱导动力学和荧光淬灭分析,解析了烟草(Nicotiana tabacum)叶片中COX途径对PSII光保护的贡献及其与AOX途径的关系。结果表明,强光处理后PSII活性在所有叶片中均下降。AOX途径受抑明显加速了叶片PSII活性的下降。而当COX途径受抑后,叶片PSII活性的下降与水处理的对照叶片无明显差异。当AOX途径与COX途径同时受抑时,叶片PSII活性的下降比单独抑制AOX途径时更严重。此外,呼吸电子传递受抑均导致叶片非光化学淬灭(NPQ)增加,AOX途径受抑导致的NPQ上调比COX途径受抑时更明显,AOX和COX途径同时受抑时NPQ的增幅最大。上述结果表明,烟草叶片中COX途径和AOX途径均参与PSⅡ的光保护。当COX途径受抑时,其光保护功能可以被AOX途径和NPQ补偿,而AOX途径的光保护作用不能被COX途径和NPQ完全补偿。     

Physiological Properties of Abscission Accelerator from Senescent Leaves

A substance which is not abscisic acid accelerates leaf abscission by regulating ethylene production.     

Role of pfkA and General Carbohydrate Catabolism in Seed Colonization by Enterobacter cloacae

Enterobacter cloacae A-11 is a transposon mutant of strain 501R3 that was deficient in cucumber spermosphere colonization and in the utilization of certain carbohydrates (D. P. Roberts, C. J. Sheets, and J. S. Hartung, Can. J. Microbiol. 38:1128–1134, 1992). In vitro growth of strain A-11 was reduced or deficient on most carbohydrates that supported growth of strain 501R3 but was unaffected on fructose, glycerol, and all amino acids and organic acids tested. Colonization by strain A-11 was significantly reduced (P ≤ 0.05) for cucumber and radish seeds compared to that of strain 501R3, but colonization of pea, soybean, sunflower, and sweet corn seeds was not reduced. Pea seeds released several orders of magnitude more total carbohydrates and amino acids than cucumber and radish seeds and approximately 4,000-fold more fructose. Fructose was the only carbohydrate detected in the seed exudates which supported wild-type levels of in vitro growth of strain A-11. Soybean, sunflower, and sweet corn seeds also released significantly greater amounts of fructose and total carbohydrates and amino acids than cucumber or radish seeds. The exogenous addition of fructose to cucumber and radish seeds at quantities similar to the total quantity of carbohydrates released from pea seeds over 96 h increased the populations of strain A-11 to levels comparable to those of strain 501R3 in sterile sand. Molecular characterization of strain A-11 indicated that the mini-Tn5 kanamycin transposon was inserted in a region of the genome with significant homology to pfkA, which encodes phosphofructo kinase. A comparison of strain A-11 with Escherichia coli DF456, a known pfkA mutant, indicated that the nutritional loss phenotypes were identical. Furthermore, the pfkA homolog cloned from E. cloacae 501R3 complemented the nutritional loss phenotypes of both E. coli DF456 and E. cloacae A-11 and restored colonization by strain A-11 to near wild-type levels. These genetic and biochemical restoration experiments provide strong evidence that the quantities of reduced carbon sources found in seed exudates and the ability of microbes to use these compounds play important roles in the colonization of the spermosphere.     

Detection of Chlorophyll Breakdown Products in the Senescent Leaves of Higher Plants

The determination of intermediary breakdown products of chlorophyllsin senescent leaves of higher plants was performed by high-performanceliquid chromatographic technique that had been newly developedto separate and identify the oxidation products of chlorophylls,in particular monopyrrole derivatives [Suzuki et al. (1999)J. Chromatogr. A 839: 85]. In six plants tested, degradationproducts were detected only in the senescent leaves of plantsincluding barley (Hordeum vulgare), except for radish (Raphanussativus), in which they were found both in pre- and senescentcotyledons. In the senescent cotyledons of barley, three degradationproducts, hematinic acid, methyl ethyl maleimide, and the putativedegraded C-E-ring derivative, methyl vinyl maleimide dialdehyde,were detected. In addition to above three products, methyl vinylmaleimide was also found in both pre- and senescent cotyledonsof radish. These products decreased during senescence with anaccumulation of unknown compound(s), probably degraded monopyrrolederivatives. The degradation process and amounts of breakdownproducts of chlorophylls depend largely on plant species andvary with length of senescence. To conclude, it is likely thatchlorophylls are degraded into low-molecular-weight hydrolyticcompounds through monopyrroles. (Received March 10, 1999; Accepted June 11, 1999)     

衰老叶片和叶绿体中超氧阴离子和有机自由基浓度的变化

以电子自旋共振波谱技术,研究从水稻、玉米、花生和苋菜的成熟及衰老叶片分离的叶绿体中O_2~-的形成,以及干燥叶绿体和叶片粉末的有机自由基。经紫外光照射后老叶叶绿体的O_2~-浓度比成熟叶增大10～249％。冷冻干燥叶绿体及烘干叶片粉末在辐照前后皆有明显的单峰信号。辐照引发两种干样中形成更多的有机自由基。老叶制备的干样不论辐照或暗下都有较高水平的自由基。以上结果表明,叶片的衰老与自由基引起的损伤有关。     

Carbohydrate Catabolism in Populations of Bursaphelenchus xylophilus and in B. mucronatus

Genotypically different host specific pathotypes of Bursaphelenchus xylophilus have been identified. These pathotypes elicit different responses in pines depending on susceptibility, tolerance, or resistance. Continued passage of some of these pathotypes on fungal cultures leads to conversion to nonparasitic populations. These populations metabolize carbon substrates to ethanol by an anaerobic pathway, while operating some level of a phosphoenolpyruvate (PEP)-succinate pathway to excrete succinate-lactate and malate. On the other hand, parasitic populations metabolize glucose to lactate-succinate, mainly by a PEP-succinate pathway, and maintain redox balance through glycerol production. Ethanol and malate are not excreted by parasitic populations.     

Effect of Pleiotropic Carbohydrate Mutations (ctr) on Tryptophan Catabolism

The pleiotropic ctr mutation has been shown to affect tryptophan uptake and tryptophanase formation. Genetic reversions are of two types: (i) complete, restoring to wild type, located at 46 to 47 min; (ii) partial, restoring only tryptophanase synthesis, located at 73 min. In some strains the effect of ctr mutations could be reversed by cyclic adenosine 3',5'-monophosphate (cAMP) plus tryptophan. A mutant producing tryptophanase constitutively was suppressed by a ctr mutation. Production of tryptophanase in this suppressed strain was not restored by the addition of cAMP, but required cAMP plus tryptophan.     

Engineered Polyamine Catabolism Preinduces Tolerance of Tobacco to Bacteria and Oomycetes

Polyamine oxidase (PAO) catalyzes the oxidative catabolism of spermidine and spermine, generating hydrogen peroxide. In wild-type tobacco (Nicotiana tabacum ‘Xanthi’) plants, infection by the compatible pathogen Pseudomonas syringae pv tabaci resulted in increased PAO gene and corresponding PAO enzyme activities; polyamine homeostasis was maintained by induction of the arginine decarboxylase pathway and spermine was excreted into the apoplast, where it was oxidized by the enhanced apoplastic PAO, resulting in higher hydrogen peroxide accumulation. Moreover, plants overexpressing PAO showed preinduced disease tolerance against the biotrophic bacterium P. syringae pv tabaci and the hemibiotrophic oomycete Phytophthora parasitica var nicotianae but not against the Cucumber mosaic virus. Furthermore, in transgenic PAO-overexpressing plants, systemic acquired resistance marker genes as well as a pronounced increase in the cell wall-based defense were found before inoculation. These results reveal that PAO is a nodal point in a specific apoplast-localized plant-pathogen interaction, which also signals parallel defense responses, thus preventing pathogen colonization. This strategy presents a novel approach for producing transgenic plants resistant to a broad spectrum of plant pathogens.     

Carbohydrate Availability and Shoot Formation in Tobacco Callus Cultures

Tobacco callus grown on a shoot-forming medium containing sorbitol or no carbon source survived, but did not produce shoots. Transfer of tissue from a sucrose medium to carbohydrate-deficient media and vice versa suggested that the growth of the tissue was a function of a total period in contact with available carbohydrate. Both starch and free sugars in the tissue were utilized during shoot initiation. Furthermore, it appeared that the continuous availability of carbohydrate was required for shoot primordium growth and/or their development into leafy vegetative shoots in dark-grown cultures.     

Correlation of Carbohydrate Catabolism and Synthesis of Macromolecules During Enzyme Synthesis in Pseudomonas fluorescens.

Kirkland, Jerry J. (Oklahoma State University, Stillwater), and Norman N. Durham. Correlation of carbohydrate catabolism and synthesis of macromolecules during enzyme synthesis in Pseudomonas fluorescens. J. Bacteriol. 90: 23-28. 1965.-Glucose, ribose, and fructose shorten the lag period required for synthesis of protocatechuate oxygenase. Radioactivity from uracil-2-C(14) is incorporated into the hot trichloroacetic acid-soluble fraction after a lag period of approximately 20 min after addition of protocatechuic acid. Addition of glucose or ribose simultaneously with the inducer shortens the lag period to approximately 5 min and increases the rate of uracil incorporation. The inducer must be present to initiate incorporation of radioactivity, and the exogenous carbon source accelerates incorporation but is not sufficient to initiate synthesis by itself. The addition of protocatechuic acid increases the rate and total incorporation of radioactivity from uniformly labeled glucose or ribose-1-C(14) into the hot trichloroacetic acid-soluble fraction. Ribose decreases the incorporation of radioactivity from uniformly labeled glucose into the hot trichloroacetic acid-soluble fraction, and glucose shows a similar effect on incorporation of radioactivity from ribose-1-C(14), indicating the two sugars are serving in the same capacity to enhance enzyme synthesis. Radioactivity from glucose-1-C(14) is not incorporated into the hot trichloroacetic acid-soluble fraction. The results suggest that glucose and ribose shorten the lag period for inducible enzyme formation by serving as a "specific" carbon source for synthesis of macromolecules such as ribonucleic acid.     

Vein Loading: The Role of the Symplast in Intercellular Transport of Carbohydrate between the Mesophyll and Minor Veins of Tobacco Leaves

Enzymatically separated leaf tissues of Nicotiana tabacum L., exhibiting good metabolic integrity, were used to evaluate the kinetics of sugar accumulation over the concentration range of 10 to 100 mm. Mesophyll cells exhibited Km values of 16 and 30 mm for glucose and sucrose, respectively; minor veins showed a reverse relationship, with Km values of 58 and 16 mm for glucose and sucrose, respectively. This would suggest that sucrose is preferentially absorbed by the minor vein net. Analysis of V(max) data indicates a reduction in the ability of isolated minor veins to accumulate substrate, implicating a symplastic rather than apoplastic route for intercellular transport. Competition studies demonstrate a common carrier for sucrose and glucose in both tissue types and suggest the presence of a "transport compartment," entry to which is regulated by a critical intracellular sucrose concentration.