Abstract. Studies of the isoprene emission rate in response to changes in photon-flux density and CO2 partial pressure were conducted using a recently developed on-line isoprene analyser combined with a gas exchange system and chlorophyll fluorometer. Upon darkening, the isoprene emission rate from leaves of aspen ( Populus tremuloides Michaux.) began to decline immediately, demonstrating that the internal pool of isoprene, or its precursors, is small and that the instantaneous emission rate is tightly coupled to the rate of synthesis. A post-illumination burst of isoprene was observed within 5 min after darkening and lasted for 15–20 min in four isoprene-emitting species that were examined. In leaves of eucalyptus ( Eucalyptus globulus Labill.), the magnitude of the post-illumination burst was dependent on the photon-flux density that existed before darkening, but not on ambient CO2 partial pressure. The dependence of the post-illumination burst on photon-flux density paralleled that for the steady-state rate of isoprene emission. A step-wise increase in intercellular CO2 partial pressure from 24.5 to 60 Pa resulted in an immediate decrease in isoprene emission rate and non-photochemical fluorescence quenching, but an increase in CO2 assimilation rate. Given the several recent studies that link isoprene emission to chloroplastic processes, the results of this study indicate that the linkage is not dependent on the rate of CO2 flux through the reductive pentose phosphate pathway, but rather on more complex relationships involving metabolites not appreciably influenced by CO2 partial pressure. 相似文献
The utilization of carbon monoxide as energy and/or carbon source by different physiological groups of bacteria is described and compared. Utilitarian CO oxidation which is coupled to the generation of energy for growth is achieved by aerobic and anaerobic eu- and archaebacteria. They belong to the physiological groups of aerobic carboxidotrophic, facultatively anaerobic phototrophic, and anaerobic acetogenic, methanogenic or sulfate-reducing bacteria. The key enzyme in CO oxidation is CO dehydrogenase which is a molybdo iron-sulfur flavoprotein in aerobic CO-oxidizing bacteria and a nickel-containing iron-sulfur protein in anaerobic ones. In carboxidotrophic and phototrophic bacteria, the CO-born CO2 is fixed by ribulose bisphosphate carboxylase in the reductive pentose phosphate cycle. In acetogenic, methanogenic, and probably in sulfate-reducing bacteria, CODH/acetyl-CoA synthase directly incorporates CO into acetyl-CoA.In plasmid-harbouring carboxidotrophic bacteria, CO dehydrogenase as well as enzymes involved in CO2 fixation or hydrogen utilization are plasmid-encoded. Structural genes encoding CO dehydrogenase were cloned from carboxidotrophic, acetogenic and methanogenic bacteria. Although they are clustered in each case, they are genetically distinct.Soil is a most important biological sink for CO in nature. While the physiological microbial groups capable of CO oxidation are well known, the type and nature of the microorganisms actually representing this sink are still enigmatic. We also tried to summarize the little information available on the nutritional and physicochemical requirements determining the sink strength. Because CO is highly toxic to respiring organisms even in low concentrations, the function of microbial activities in the global CO cycle is critical. 相似文献
The activity of the enzyme responsible for the conversion of norsolorinic acid to averantin was studied in two strains of Aspergillus parasiticus. Cell-free extracts of the enzyme were purified from different aged mycelia and little activity was found prior to 24 hours after inoculation but this quickly reached a maximum at 48 hours and declined thereafter. Both strains of A. parasiticus, one in aflatoxin producing strain, the other a versicolorin A accumulating mutant, showed this trend. It was concluded that the enzyme responsible for this conversion was a secondary metabolic enzyme and was distinct from alcohol and mannitol dehydrogenases. 相似文献
1. 1.|Changes in tissue metabolite concentrations and enzyme activities in the pedipalpal (PM) and heart (HM) muscles of the tropical scorpion Heterometrus fulvipes show that the metabolism in PM and HM is fundamentally reorganized following low (18°C) and high (38°C) temperature acclimation.
2. 2.|Changes in metabolite concentrations show that metabolite biosynthesis showed increases after cold acclimation but decreases after warm acclimation.
3. 3.|Similarly, changes in enzyme activities show a preponderance of glycolysis and HMP shunt activity after cold acclimation, while after warm acclimation glycogenolysis, oxidative metabolism and gluconeogenesis predominated.
4. 4.|Higher metabolite concentrations and enzyme activities both before and after thermal acclimation in HM reflect its greater compensatory abilities.
Abstract Multiple antibiotic-resistant Shigella dysenteriae type 1 isolates from a recent epidemic in West Bengal (India) showed identical plasmid patterns. All isolates were resistant to ampicillin (Am), chloramphenicol (Cm), tetracycline (Tc), streptomycin (Sm) and trimethoprim (Tp) and contained 6 plasmids, ranging from 2.5–120 kb. The Am resistance determinant was located on the 120 kb plasmid. This plasmid was unstable when the S. dysenteriae strains were grown above 37°C. The Bangladesh strains of S. dysenteriae type 1 showed identical plasmid patterns, except that many isolates were Am-sensitive and lacked the 120 kb plasmid. In strains from both Bangladesh and West Bengal, predominantly group-B plasmids conferred resistance to Cm and Tc. Comparisons of Eco R1 fragments generated from the total plasmid DNA content of each strain support the view that the plasmids present in the S. dysenteriae type 1 strains isolated from all recent epidemics in India and Bangladesh were identical. 相似文献
Summary The seasonal occurrence ofAtyaephyra desmaresti in The Netherlands has been studied by sampling the cooling-water filtering screens of power stations situated along the rivers Rhine and Meuse. The shrimps were only found in large numbers at the two power stations with vegetation in the cooling-water intake areas. Fluctuations in the seasonal occurrence showed great similarity for these two localities. Highest numbers of shrimps were impinged in November. High numbers also occurred in September, while a lower peak in numbers was found in May.Changes in the numbers of records during the last 30 years in The Netherlands were compared with climatological fluctuations (severe or mild winters), indicating that this mainly southern-European species is living here at the limits of its ecological and geographical range.The distribution in The Netherlands reveals thatAtyaephyra desmaresti mainly occurs in freshwater habitats, although it tolerates higher chlorinities. 相似文献
The effect of phorbol myristate acetate, phorbol dibutyrate, ethanol, dimethylsulfoxide, phenol, and seven metabolites of phenol on metabolic cooperation were assessed as a function of mutant cell recovery from populations of cocultivated hypoxanthine-guanine phosphoribosyl transferase-deficient mutant (HGPRT–) and wild-type (HGPRT+) Chinese hamster V79 lung fibroblasts. Phorbol myristate acetate and phorbol diputyrate, two established tumor promoters, were potent inhibitors of metabolic cooperation. Ethanol and dimethylsulfoxide, solvents commonly used to prepare chemicals for testing, weakly inhibited metabolic cooperation. Phenol and phenylglucuronide had no effect on metabolic cooperation. Four oxidative metabolites (1,4-benzoquinone, catechol, hydroxyquinol and quinol) inhibited metabolic cooperation. Phenylsulfate weakly inhibited metabolic cooperation. Conversely, 2-methoxyphenol, a methylated derivative of catechol, appeared to enhance metabolic cooperation. These results generallyAbbreviations CAS
Chemical Abstracts Service
- DMSO
dimethylsulfoxide
- ETOH
ethanol
- HGPRT
hypoxanthine-guanine phosphoribosyl transferase
- HGPRT+
HGPRT-competent
- HGPRT–
HGPRT-te]deficient
- MC
metabolic cooperation
- MC+
metabolic cooperation-competent
- MC–
metabolic cooperation-deficient
- MEM
minimum essential medium
- PDBu
phorbol dibutyrate
- PMA
phorbol myristate acetate
- 6TG
6-thioguanine
- 6TGr
6-thioguanine-resistant
- 6TGs
6-thioguanine-sensitive
- V79/MC assay
Chinese hamster V79 lung fibroblast assay for metabolic cooperation 相似文献