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91.
Ethylene has been shown to stimulate the degradation of indole-3-acetic acid (IAA) in citrus leaf tissues via the oxidative decarboxylation pathway, resulting in the accumulation of indole-3-carboxylic acid (ICA). Preliminary data indicated that ethylene stimulates only the first step of this pathway, i.e. the decarboxylation of IAA which leads to the formation of indole-3-methanol. The effect of ethylene seems to be a specific one since 2,5-norbornadiene, an ethylene action inhibitor, significantly inhibited the stimulation of IAA decarboxylation by ethylene. It has long been suggested that peroxidase or a specific form of the peroxidase complex (`IAA oxidase') catalyse this step. However, we did not observe a clear effect of ethylene on the peroxidase system. An alternative possibility, that the stimulatory effect of ethylene on IAA catabolism results from increased formation of hydrogen peroxide (H2O2), a co-factor for peroxidase activity, was verified by direct measurements of H2O2 in the tissues or by assaying the activity of gluthathione reductase, which has been shown to be induced by oxygen species. This possibility is further supported by the observations showing that IAA decarboxylation in control tissues was enhanced to the level detected in ethylene-treated tissues by application of H2O2. 相似文献
92.
The effect of different osmolytes on the viability and the effect of osmotic pressure on the induction of a dormant state similar to that caused by a slow desiccation rate were evaluated in the entomopathogenic nematode Steinernema carpocapsae ‘All’. For both experiments, a high-temperature (45°C) assay (HTA) was employed. Exposing fresh infective juveniles to the HTA resulted in a drastic reduction in viability. Using the same assay, the mortality of desiccated nematodes was gradual, showing an enhanced ability to withstand high-temperature conditions. The patterns of decline in viability in the evaporatively dehydrated and the osmotically desiccated nematodes were similar. Most of the salts tested in the screening assay caused high mortality levels among the nematodes within the first 24 h of exposure. In contrast, the nonionic solutes tested did not hamper the viability of the infective juveniles. In these nonionic solutions, all nematodes were completely shrunk after 48 h. Furthermore, 72-h exposure to these solutions resulted in an increase in heat tolerance similar to that of the evaporatively dehydrated nematodes. A substantial increase in heat tolerance was recorded in the treatments with glycerol solutions at concentrations from 2.2 to 3.8 M. A similar effect was obtained by polyethylene glycol (PEG) 300 MW at concentrations ranging from 1.2 to 1.6 M. PEG 600 MW induced enhancement of heat tolerance at a concentration of 0.8 M. A high level of viability was attained among nematodes that were stored for 72 days following a gradual increase in glycerol concentrations. Exposure of these nematodes to 45°C in the HTA resulted in 87.3 ± 4.7 and 49.2 ± 3.9% survival after 4 and 8 h, respectively. Reduction in viability was observed among nematodes that were directly exposed to the glycerol solution over a 19-day storage period. With this treatment, survival levels of 72.7 ± 3.9 and 26.5 ± 4.7% after 4 and 8 h, respectively, were recorded in the HTA. Reduction in viability among nematodes stored in distilled water was noted after 36 days of storage. Evaluation of nematode infectivity by two criteria (insect mortality and invasion rate) indicated that infectivity of nematodes desiccated by gradual osmotic pressure induced by glycerol was similar to that of fresh nematodes after 54 days in storage at 25°C. In comparison, infectivity of nematodes stored in distilled water declined significantly compared to that of fresh nematodes. 相似文献
93.
Edward Averbukh Michael Halpert Ravit Yanko Lutza Yanko Jacob Peèr Samuel Levinger Allan Flyvbjerg Itamar Raz 《Experimental diabetes research》2000,1(1):39-47
Objective: Octreotide, a somatostatin analogue, has
been shown to prevent angiogenesis in diverse in
vitro models. We evaluated its effect on retinal neovascularization
in vivo, using a neonatal rat retinopathy
model.
Methods: We used, on alternating days, hypoxia
(10% O2) and hyperoxia (50% O2) during the first 14
days of neonatal rats, to induce retinal neovascularization.
Half of the rats were injected subcutaneously
with octreotide 0.7 μg/g BW twice daily. At
day 18 the eyes were evaluated for the presence of
epiretinal and vitreal hemorrhage, neovascularization
and epiretinal proliferation. Octreotide pharmacokinetics
and its effect on serum growth hormone
(GH) and insulin-like growth factor I (IGF-I) were
examined in 28 rats.
Results: Serum octreotide levels were 667 μg/1 two
hours after injection, 26.4 μg/1 after nine hours and
3.2 μg/1 after 14 hours. GH levels were decreased
by 40% (p = 0.002) two hours after injection but
thereafter returned to baseline. IGF-I levels were unchanged
two hours after injection and were elevated
by 26% 14 hours after injection (p = 0.02). Epiretinal
membranes were highly associated with epiretinal
hemorrhages (p < 0.001), while retinal neovascularization
was notably associated with vitreal hemorrhages (p < 0.001).
Conclusions: Twice-daily injections of octreotide
failed to produce sustained decrease in serum GH,
but produced rebound elevation of serum IGF-I.
Accordingly, no statistically significant effect of injections
on retinal pathology was noted. This finding,
however, does not contradict our assumption
that GH suppression may decrease the severity of
retinopathy. 相似文献
94.
95.
Trehalose dimycolate, a glycolipid component of the cell walls of mycobacteria, induces interstitial pneumonitis and alveolar hemorrhages in C57BL/6 and C57BL/10 mice. Homozygous nude (nu/nu) mice of these backgrounds are not susceptible to this form of pulmonary injury. However, after administration of T-lymphocyte-enriched spleen cell preparations from syngeneic donors, homozygous nude mice become susceptible to trehalose dimycolate. The observations suggest that production of pulmonary lesions by this mycobacterial component is dependent on T lymphocytes. While the mechanisms are still under study, we propose that trehalose dimycolate can function as an activator of T lymphocytes and that products of activated T cells are responsible for production of the pulmonary lesions. 相似文献
96.
Robert J. Warren Katherine J. Elliott Itamar Giladi Joshua R. King Mark A. Bradford 《Ecological Entomology》2019,44(1):30-39
1. Some interactions previously described as mutualistic were revealed to be commensal or parasitic in subsequent investigations. Ant‐mediated seed dispersal has been described as a mutualism for more than a century; however, recent research suggests that it may be commensal or parasitic. Plants demonstrably benefit from ant‐mediated seed dispersal, although there is little evidence available to demonstrate that the interaction benefits long‐term ant fitness. 2. Field experiments were conducted in temperate North America focused on a key seed‐dispersing ant. All herbaceous plants were removed from a forest understorey for 13 years, and supplemented ant colonies with large elaiosome‐bearing seeds aiming to examine potential long‐ and short‐term myrmecochorous plant benefits for the ants. 3. If elaiosome‐bearing seeds benefit ants, suggesting a mutualistic relationship, it is expected that there would be greater worker and/or alate abundance and greater fat reserves (colony lipid content) with seed supplementation (short‐term) and in areas with high understorey herb abundance. 4. Short‐term seed supplementation of ant colonies did not result in an increase with respect to numbers or fat stores, although it did prompt the production of colony sexuals, which is a potential fitness benefit. In the long term, however, there was no positive effect on the ants and, instead, there were negative effects because the removal of elaiosome‐bearing plants corresponded with greater colony health. 5. The data obtained in the present study suggest that the ant–plant interaction ranged from occasionally beneficial to neutral to overall negative for the ant partner. Such results did not support considering the interaction as a mutualism. Collectively, the data suggest the need to reconsider the nature of the relationship between these ants and plants. 相似文献
97.
98.
Philip J. Scarpace Stephen W. OConnor Itamar B. Abrass 《Biochimica et Biophysica Acta (BBA)/Molecular Cell Research》1985,845(3):520-525
Cholesterol, a major structural component of plasma membranes, has a profound influence on cell surface receptor characteristics and on adenylate cyclase activity. β-Adrenergic receptor number, adenylate cyclase activity, and receptor-cyclase coupling were assessed in rat lung membranes following preincubation with cholesteryl hemisuccinate. β-Adrenergic receptor number increased by 50% without a change in antagonist affinity. However, β-adrenergic receptor affinity for isoproterenol increased 2-fold as a result of an increase in the affinity of the isoproterenol high-affinity binding site. This increase in agonist affinity did not potentiate hormone-stimulated adenylate cyclase activity, which decreased 3-fold following cholesterol incorporation. However, the ratio of isoproterenol to GTP-stimulated activity was unchanged with cholesterol. Stimulation distal to the receptor by GTP, NaF, GppNHp, Mn2+ and forskolin also demonstrated 50–80% reduced enzyme activity following cholesterol incorporation. These data suggest that membrane cholesterol incorporation decreases catalytic unit activity without affecting transduction of the hormone signal. 相似文献
99.
Effect of 2,5-norbornadiene on abscission and ethylene production in citrus leaf explants 总被引:4,自引:0,他引:4
Citrus ( Citrus sinensis L. Osbeck) leaf explants completely abscise within 48 h when exposed to saturating amounts of ethylene at 25°C. When 2,5-norbornadiene was added, 2000 μl 1−1 reduced abscission of explants also exposed to 2 μl 1−1 of ethylene to the level of the control, and 8000 μl 1−1 reduced abscission in explants exposed to 10 μl 1−1 of ethylene to the level of the control, but abscission was complete when 1 000 μl 1−1 of ethylene was used in the presence of 8 000 μl 1−1 of 2,5-norbornadiene. When explants were exposed to 2 μl 1−1 of ethylene, 2000 μl 1−1 of 2,5-norbornadiene prevented abscission if applied up to 10 h after exposure to ethylene. After 18 h, applied 2,5-norbornadiene had little effect on abscission at 48 h. A Lineweaver-Burk plot gave a 1/2 maximum value of 0.12 μl 1−1 for ethylene on abscission, 2,5-Norbornadiene gave competitive kinetics with respect to ethylene with a K1 value of approximately 120 μl 1−1 of 2,5-norbornadiene. The presence of 2,5norbornadiene stimulated ethylene production, which progressively increased as the 2,5-norbornadiene concentration was increased from 250 to 8 000 μl 1−1 2,5-Norbornadiene also suppressed the induction of cellulase and polygalacturonase by ethylene. Together, 2,5-norbornadiene and 2,4-dichlorophenoxyacetic acid were more effective than either alone in reducing abscission. 2,5-Norbornadiene also was effective in preventing the reduction of indole-3-acetic acid transport induced by ethylene. 相似文献
100.
Directed evolution of an endoinulinase from Talaromyces purpureogenus toward efficient production of inulooligosaccharides
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Livnat Afriat‐Jurnou Rami Cohen Irina Paluy Ran Ben‐Adiva Itamar Yadid 《Biotechnology progress》2018,34(4):868-877
Inulinases are fructofuranosyl hydrolases that target the β‐2,1 linkage of inulin and hydrolyze it into fructose, glucose and inulooligosaccharides (IOS), the latter are of growing interest as dietary fibers. Inulinases from various microorganisms have been purified, characterized and produced for industrial applications. However, there remains a need for inulinases with increased catalytic activity and better production yields to improve the hydrolysis process and fulfill the growing industrial demands for specific fibers. In this study, we used directed enzyme evolution to increase the yield and activity of an endoinulinase enzyme originated from the filamentous fungus Talaromyces purpureogenus (Penicillium purpureogenum ATCC4713). Our directed evolution approach yielded variants showing up to fivefold improvements in soluble enzyme production compared to the starting point which enabled high‐yield production of highly purified recombinant enzyme. The distribution of the enzymatic reaction products demonstrated that after 24 h of incubation, the main product (57%) had a degree of polymerization of 3 (DP3). To the best of our knowledge, this is the first application of directed enzyme evolution to improve inulooligosaccharide production. The approach enabled the screening of large genetic libraries within short time frames and facilitated screening for improved enzymatic activities and properties, such as substrate specificity, product range, thermostability and pH optimum. © 2018 American Institute of Chemical Engineers Biotechnol. Prog., 34:868–877, 2018 相似文献