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171.
This paper 1) reviews improvements and new approaches in methodologies for estimating biological N2 fixation (BNF) in wetland soils, 2) summarizes earlier quantitative estimates and recent data, and 3) discusses the contribution of BNF to N balance in wetland-rice culture.Measuring acetylene reducing activity (ARA) is still the most popular method for assessing BNF in rice fields. Recent studies confirm that ARA measurements present a number of problems that may render quantitative extrapolations questionable. On the other hand, few comparative measures show ARA's potential as a quantitative estimate. Methods for measuring photodependent and associative ARA in field studies have been standardized, and major progress has been made in sampling procedures. Standardized ARA measurements have shown significant differences in associative N2 fixation among rice varieties.The 15N dilution method is suitable for measuring the percentage of N derived from the atmosphere (% Ndfa) in legumes and rice. In particular, the 15N dilution technique, using available soil N as control, appears to be a promising method for screening rice varieties for ability to utilize biologically fixed N. Attempts to adapt the 15N dilution method to aquatic N2 fixers (Azolla and blue-green algae [BGA]) encountered difficulties due to the rapid change in 15N enrichment of the water.Differences in natural 15N abundance have been used to show differences among plant organs and species or varieties in rice and Azolla, and to estimate Ndfa by Azolla, but the method appears to be semi-quantitative.Recent pot experiments using stabilized 15N-labelled soil or balances in pots covered with black cloth indicate a contribution of 10–30 kg N ha-1 crop-1 by heterotrophic BNF in flooded planted soil with no or little N fertilizer used.Associative BNF extrapolated from ARA and 15N incorporation range from 1 to 7 kg N ha-1 crop-1. Straw application increases heterotrophic and photodependent BNF. Pot experiments show N gains of 2–4 mg N g-1 straw added at 10 tons ha-1.N2 fixation by BGA has been almost exclusively estimated by ARA and biomass measurements. Estimates by ARA range from a few to 80 kg N ha-1 crop-1 (average 27 kg). Recent extensive measurements show extrapolated values of about 20 kg N ha-1 crop-1 in no-N plots, 8 kg in plots with broadcast urea, and 12 kg in plots with deep-placed urea.Most information on N2 fixed by Azolla and legume green manure comes from N accumulation measurements and determination of % Ndfa. Recent trials in an international network show standing crops of Azolla averaging 30–40 kg N ha-1 and the accumulation of 50–90 kg N ha-1 for two crops of Azolla grown before and after transplanting rice. Estimates of % Ndfa in Azolla by 15N dilution and delta 15N methods range from 51 to 99%. Assuming 50–80% Ndfa in legume green manures, one crop can provide 50–100 kg N ha-1 in 50 days. Few balance studies in microplots or pots report extrapolated N gains of 150–250 kg N ha-1 crop-1.N balances in long-term fertility experiments range from 19 to 98 kg N ha-1 crop-1 (average 50 kg N) in fields with no N fertilizer applied. The problems encountered with ARA and 15N methods have revived interest in N balance studies in pots. Balances are usually highest in flooded planted pots exposed to light and receiving no N fertilizer; extrapolated values range from 16 to 70 kg N ha-1 crop-1 (average 38 kg N). A compilation of balance experiments with rice soil shows an average balance of about 30 kg N ha-1 crop-1 in soils where no inorganic fertilizer N was applied.Biological N2 fixation by individual systems can be estimated more or less accurately, but total BNF in a rice field has not yet been estimated by measuring simultaneously the activities of the various components in situ. As a result, it is not clear if the activities of the different N2-fixing systems are independent or related. A method to estimate in situ the contribution of N2 fixed to rice nutrition is still not available. Dynamics of BNF during the crop cycle is known for indigenous agents but the pattern of fixed N availability to rice is known only for a few green manure crops. 相似文献
172.
E.V. Nikolaeva A.I. Usov A.P. Sinitsyn A.H. Tambiev 《Journal of applied phycology》1999,11(4):385-389
Several new crude enzyme preparations were isolated from a marine association of the agarolytic bacterium Cytophaga diffluens
and the infusorium Uronema marinum, an axenic culture of Cytophaga diffluens, some species of land micro- and macromycetes
adapted to assimilate red algal biomass and from the marine mollusc Littorina littorea. Fungal and mollusc enzyme preparations
were shown to have cellulase, xylanase, protease and agarase activities. Fungal agarase activity was revealed only after 3–4
passages of the culture on the medium containing algal biomass. Enzyme preparations from the association and the pure bacterial
culture growing on the medium with bactoagar as the sole carbon source contained only agarase activity. The maximum specific
agarase activity was found in a preparation from the marine association. The preparations obtained can be used for isolating
protoplasts and single cells from red seaweed thalli.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
173.
Aleksandro S. Da Silva Luziane P. Bellé Paula E.R. Bitencourt Herakles A. Garcia Perez Gustavo R. Thomé Marcio M. Costa Camila B. Oliveira Marta M.G. Teixeira Maria B. Moretto Cinthia M. Mazzanti Sonia T.A. Lopes Silvia G. Monteiro 《Experimental parasitology》2011,(1):173-177
The study was undertaken to evaluate changes in the activity of adenosine deaminase (ADA) in brains of rats infected by Trypanosoma evansi. Each rat was intraperitoneally infected with 106 trypomastigotes either suspended in fresh (group A; n = 13) and cryopreserved blood (group B; n = 13). Thirteen animals were used as control (group C). ADA activity was estimated in the cerebellum, cerebral cortex, striatum and hippocampus. No differences (P > 0.05) in ADA activity were observed in the cerebellum between infected and non-infected animals. Significant (P < 0.05) reductions in ADA activity occurred in cerebral cortex in acutely (day 4 post-infection; PI) and chronically (day 20 PI) infected rats. ADA activity was significantly (P < 0.05) decreased in the hippocampus in acutely infected rats, but significantly (P < 0.05) increased in the chronically infected rats. Significant (P < 0.05) reductions in ADA activity occurred in the striatum of chronically infected rats. Parasites could be found in peripheral blood and brain tissue through microscopic examination and PCR assay, respectively, in acutely and chronically infected rats. The reduction of ADA activity in the brain was associated with high levels of parasitemia and anemia in acute infections. Alterations in ADA activity of the brain in T. evansi-infected rats may have implications for pathogenesis of the disease. 相似文献
174.
Silkworm hemolymph contains unique proteins that exhibit anti-apoptotic activity in mammalian cells. Among them, 30 K protein, which is one of the major anti-apoptotic molecules in silkworm hemolymph, has been well investigated. However, little is known about the biological functions of storage protein 1 (SP1), another main protein in silkworm hemolymph. In this study, the anti-apoptotic and anti-oxidative activities of SP1 were analyzed. A stable cell line expressing SP1 was constructed, which showed strong anti-apoptotic effect induced by staurosporine treatment. In addition, the cell line exhibited resistance to oxidative stress caused by hydrogen peroxide. For practical applications of SP1, recombinant SP1 was produced in Escherichia coli, and the supplementation of recombinant SP1 into culture medium exhibited anti-apoptotic and anti-oxidative activities. In addition, SP1 was found to be a cell-penetrating protein and localized in the cytosol as well as on the plasma membrane. The findings showed that SP1 itself is not an anti-oxidant; rather, it mediates intracellular anti-oxidative activity. In conclusion, the cellular resistance of SP1 to apoptosis and oxidative stress will provide a new strategy that could be utilized in the bio-industry for the production of biologics as well as for the development of anti-aging cosmetics. 相似文献
175.
176.
When kinetin was applied to the source organ (flag leaf) of rice (Oryza sativa L. cv. Ratna), foliar senescence was delayed and grain yield per plant (as evidenced by grain weight, grain/straw weight ratio and 1,000 grain growth) was increased through the increase of sink activity (increase in dry weight of the grains/plant), duration of sink capacity as well as photosynthetic ability of the glumes (as determined by the chlorophyll content of the glumes of the developing grains). However, application of kinetin to the sink organs (fruits), promoted senescence of the source but increased the yield by increasing the sink capacity and 1,000 grain growth mostly at the earlier stage of reproductive development. Lower sterility percentage was associated with higher grain yield of the plant by kinetin treatments. ABA applied either to the source or the sink promoted leaf senescence and reduced the grain yield by reducing the sink activity, harvest index, sink capacity duration and increasing the sterility percentage. Thousand grain dry weight at harvest did not vary significantly amongst the treatments. It was concluded that nutrient drainage was associated with the correlative influence of fruit on the monocarpic senescence of rice plant and that a competetion for differential allocation of cytokinin and ABA in the source and sink organs initiates this senescence syndrome. 相似文献
177.
Shima Rajaei Saeed Karima Hessam Sepasi Tehrani Somayeh Shateri Somayeh Mahmoodi Baram Meisam Mahdavi Farzad Mokhtari Alimohammad Alimohammadi Abbas Tafakhori Abolfazl Amiri Vajiheh Aghamollaii Hamid Fatemi Masoumeh Rajabibazl Farzad Kobarfard Ali Gorji 《Journal of neurochemistry》2020,155(2):207-224
178.
Chemical compositions and antimicrobial activities of four different Anatolian propolis samples 总被引:5,自引:0,他引:5
Propolis means a gum that is gathered by bees from various plants. It is known for its biological properties, having antibacterial, antifungal and healing properties. The aims of this study were to evaluate the antimicrobial activity of four different Anatolian propolis samples on different groups of microorganisms including some oral pathogens and comparison between their chemical compositions. Ethanol extracts of propolis (EEP) were prepared from four different Anatolian propolis samples and examined whether EEP inhibit the growth of the test microorganisms or not. For the antimicrobial activity assays, minimum inhibitory concentrations (MIC) were determined by using macrodilution method. The MIC values of the most effective propolis (TB) were 2 microg/ml for Streptococcus sobrinus and Enterococcus faecalis, 4 microg/ml for Micrococcus luteus, Candida albicans and C. krusei, 8 microg/ml for Streptococcus mutans, Staphylococcus aureus, Staphylococcus epidermidis and Enterobacter aerogenes, 16 microg/ml for Escherichia coli and C. tropicalis and 32 microg/ml for Salmonella typhimurium and Pseudomonas aeruginosa. The chemical compositions of EEP's were determined by high-temperature high-resolution gas chromatography coupled to mass spectrometry. The main compounds of four Anatolian propolis samples were flavonoids such as pinocembrin, pinostropin, isalpinin, pinobanksin, quercetin, naringenin, galangine and chrysin. Although propolis samples were collected from different regions of Anatolia all showed significant antimicrobial activity against the Gram positive bacteria and yeasts. Propolis can prevent dental caries since it demonstrated significant antimicrobial activity against the microorganisms such as Streptococcus mutans, Streptococcus sobrinus and C. albicans, which involves in oral diseases. 相似文献
179.
Seven 9,10-seco-9,19-cyclolanostane arabinosides, named podocarpasides A-G (1-7), were isolated from the roots of Actaea podocarpa DC., a species closely related to black cohosh (a well known dietary supplement). Their structures were determined with the help of spectroscopic data including extensive 2D NMR spectroscopy. The isolates were found inactive, when tested for cytotoxic, estrogenic, and antioxidant activities in cell based assays. They were also tested for anticomplement activity against the classical pathway of complement system and only podocarpaside C (3) inhibited modest complement activity with an IC50 value of 200 microM. 相似文献
180.