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971.
Delgado-Méndez P Herrera N Chávez H Estévez-Braun A Ravelo AG Cortes F Castanys S Gamarro F 《Bioorganic & medicinal chemistry》2008,16(3):1425-1430
Two new sesquiterpenes (1-2) and one new lupane triterpene (3) have been isolated from the roots of Maytenus apurimacensis. The novel beta-dihydroagarofurans are the first sesquiterpenes with a basic polyhydroxy skeleton of 15-deoxyalatol and 4,15-dideoxyalatol that show high MDR reversing activity in the protozoan parasite Leishmania tropica. 相似文献
972.
Fernández V Tapia G Varela P Gaete L Vera G Mora C Vial MT Videla LA 《Free radical biology & medicine》2008,44(9):1724-1731
Hepatic ischemia-reperfusion (IR) injury, a major clinical drawback during surgery, is abolished by L-3,3',5-triiodothyronine (T(3)) administration. Considering that the triggering mechanisms are unknown, the aim of this study is to assess the role of oxidative stress in T(3) preconditioning using N-acetylcysteine (NAC) before T(3) administration. Male Sprague-Dawley rats given a single dose of 0.1 mg of T(3)/kg were subjected to 1 h ischemia followed by 20 h reperfusion, in groups of animals pretreated with 0.5 g of NAC/kg 0.5 h before T(3) or with the respective control vehicles. At the end of the reperfusion period, blood and liver samples were taken for analysis of serum aspartate aminotransferase (AST) and hepatic histology, glutathione (GSH) and protein carbonyl contents, and nuclear factor-kappaB (NF-kappaB) and activating protein 1 (AP-1) DNA binding. The IR protocol used led to a 4.5-fold increase in serum AST levels and drastic changes in liver histology, with significant GSH depletion and enhancement of protein carbonyl levels and of the protein carbonyl/GSH content ratio, whereas NF-kappaB and AP-1 DNA binding was decreased and enhanced, respectively. In a time window of 48 h, T(3) exerted protection against hepatic IR injury, with 88% reduction in the protein carbonyl/GSH ratio and normalization of NF-kappaB and AP-1 DNA binding, changes that were suppressed by NAC administration before T(3). Data presented suggest that a transient increase in the oxidative stress status of the liver is an important trigger for T(3) preconditioning, evidenced in a warm IR injury model through antioxidant intervention. 相似文献
973.
Reverse signaling by ephrin-As upon binding EphAs controls axon guidance and mapping. Ephrin-As are GPI-anchored to the membrane, requiring that they complex with transmembrane proteins that transduce their signals. We show that the p75 neurotrophin receptor (NTR) serves this role in retinal axons. p75(NTR) and ephrin-A colocalize within caveolae along retinal axons and form a complex required for Fyn phosphorylation upon binding EphAs, activating a signaling pathway leading to cytoskeletal changes. In vitro, retinal axon repulsion to EphAs by ephrin-A reverse signaling requires p75(NTR), but repulsion to ephrin-As by EphA forward signaling does not. Constitutive and retina-specific p75(NTR) knockout mice have aberrant anterior shifts in retinal axon terminations in superior colliculus, consistent with diminished repellent activity mediated by graded ephrin-A reverse signaling induced by graded collicular EphAs. We conclude that p75(NTR) is a signaling partner for ephrin-As and the ephrin-A- p75(NTR) complex reverse signals to mediate axon repulsion required for guidance and mapping. 相似文献
974.
975.
Ricardo Louro Laura M. Santiago Antonio dos Santos Raul Machado 《Trees - Structure and Function》2003,17(1):11-22
The young and expanded leaf micromorphology and ultrastructure of Eucalyptus grandis 2 E. urophylla juvenile plants, cultivated in greenhouse and field conditions, were analyzed by scanning and transmission electron microscopy. In greenhouse leaves epicuticular wax needles covered the abaxial and adaxial surfaces. On the adaxial surface, the needles form an atypical arrangement in lines, mainly over the anticlinal wall of epidermis cells. After plant transfer to field conditions, the organization of epicuticular wax was altered forming amorphous layers on the adaxial leaf surface, in contrast to the abaxial surface, which maintained the wax needle cover. In both culture conditions the lamellar cuticle formed on the young leaves surface disappeared during leaf enlargement. The ex vitro environment induced the development of hypostomatic leaves. The dorsiventral organization of greenhouse leaves was replaced by an isobilateral arrangement in field conditions with concomitant aerial space reduction. Results suggest that those structural changes may be some of the strategies to avoid excessive plant transpiration during Eucalyptus hybrid plants' acclimatization. 相似文献
976.
Diego F. Segura Carlos Cáceres M. Teresa Vera Viwat Wornoayporn Amirul Islam Peter E.A. Teal Jorge L. Cladera Jorge Hendrichs & Alan S. Robinson 《Entomologia Experimentalis et Applicata》2009,131(1):75-84
Methoprene (a mimic of juvenile hormone) treatment can reduce the time required for sexual maturation in Anastrepha fraterculus (Wiedemann) (Diptera: Tephritidae) males under laboratory conditions, supporting its use as a treatment for sterile males within the context of the sterile insect technique (SIT). We evaluated sexual behaviour, mating competitiveness of methoprene-treated males, and female readiness to mate after methoprene-treatment in field cages. The study involved two strains of A. fraterculus from Argentina and Peru, which show several polymorphisms in relation to their sexual behaviour. We also analyzed whether methoprene treatment affected male and/or female behaviour in the same way in these two strains. Methoprene-treated males were equally competitive with untreated mature males, and became sexually competitive 6 days after emergence (3–4 days earlier than untreated males). In contrast, methoprene did not induce sexual maturation in females or, at least, it did not induce a higher rate of mating in 7-day-old females. These results were observed both for the Argentina and the Peru strains. Altogether, our results indicate that methoprene treatment produces sexually competitive males in field cages. In the absence of a genetic sexing system, and when sterile males and females of A. fraterculus are released simultaneously, the fact that females do not respond as do males to the methoprene treatment acts as a physiological sexing effect. Therefore, in the presence of mainly sexually immature sterile females, released sexually mature sterile males would have to disperse in search of wild fertile females, thereby greatly reducing matings among the released sterile insects and thus enhancing sterile insect technique efficiency. 相似文献
977.
Zornitsa Katerova Sergei Ivanov Sergio Mapelli Vera Alexieva 《Acta Physiologiae Plantarum》2009,31(1):111-117
Pea (Pisum sativum L.) seedlings were exposed to low, moderate, and high regimes of ultraviolet-B (UV-B) (ld-B 4.4, md-B 13.3, and hd-B 26.5 kJ m−2 day−1), or ultraviolet-C (UV-C) (ld-C 0.1, md-C 0.3, and hd-C 0.6 kJ m−2 day−1) radiations. Concentrations of total phenols, free proline, and low-molecular thiol groups were determined in the last formed
(young) and older leaves after irradiation for 7, 10 or 14 consecutive days. Shoot length and weight did not change markedly
after 14 days of ld-B and ld-C, but reduced substantially after moderate and high regimes of both UV-B and UV-C. Proline decreased
upon high doses of irradiation, while in ld-B treated plants, by contrast, an increase was observed. The reduction in total
phenols and thiols was stronger after hd-B than after hd-C irradiations, although an induction was found in ld-B treated plants.
In contrast to ld-B, ld-C regime led mainly to reductions or insignificant changes in proline, phenols, and thiols. Therefore,
the stress-protection mechanisms are different between low UV-B and UV-C irradiation regimes in regard to proline, phenols,
and thiols. 相似文献
978.
Elke De Vuyst Nan Wang Elke Decrock Marijke De Bock Mathieu Vinken Marijke Van Moorhem Charles Lai Maxime Culot Vera Rogiers Romeo Cecchelli Christian C. Naus W. Howard Evans Luc Leybaert 《Cell calcium》2009,46(3):176-187
Connexin hemichannels have a low open probability under normal conditions but open in response to various stimuli, forming a release pathway for small paracrine messengers. We investigated hemichannel-mediated ATP responses triggered by changes of intracellular Ca2+ ([Ca2+]i) in Cx43 expressing glioma cells and primary glial cells. The involvement of hemichannels was confirmed with gja1 gene-silencing and exclusion of other release mechanisms. Hemichannel responses were triggered when [Ca2+]i was in the 500 nM range but the responses disappeared with larger [Ca2+]i transients. Ca2+-triggered responses induced by A23187 and glutamate activated a signaling cascade that involved calmodulin (CaM), CaM-dependent kinase II, p38 mitogen activated kinase, phospholipase A2, arachidonic acid (AA), lipoxygenases, cyclo-oxygenases, reactive oxygen species, nitric oxide and depolarization. Hemichannel responses were also triggered by activation of CaM with a Ca2+-like peptide or exogenous application of AA, and the cascade was furthermore operational in primary glial cells isolated from rat cortex. In addition, several positive feed-back loops contributed to amplify the responses. We conclude that an elevation of [Ca2+]i triggers hemichannel opening, not by a direct action of Ca2+ on hemichannels but via multiple intermediate signaling steps that are adjoined by distinct signaling mechanisms activated by high [Ca2+]i and acting to restrain cellular ATP loss. 相似文献
979.
Santiago Nava Atilio J. Mangold Mariano Mastropaolo José M. Venzal Elena B. Oscherov Alberto A. Guglielmone 《Systematic parasitology》2009,73(3):161-174
All parasitic stages of Amblyomma boeroi n. sp. (Acari: Ixodidae) are described here from Catagonus wagneri (Rusconi) in Argentina. The diagnostic characters for the male are a combination of orbited eyes, a 2/2 dental formula, coxa
IV considerably larger than coxae I–III and with a long, sickle-shaped, medially directed spur arising from its internal margin,
a scutum which is light grey to very pale ivory in colour, and the absence of a postanal groove. The diagnostic characters
for the females are a combination of orbited eyes, a central pair and two marginal pairs of short, coarse notal setae, a 2/2
dental formula, and the absence of a postanal groove. The nymph has short palpi and a 2/2 dental formula arranged in 6 rows,
its eyes are convex and orbited, and it has no postanal groove. The dorsally rectangular basis capituli of the larva, its bulging eyes and slightly sinuous posterior scutal margin all serve to distinguish it from the larva of
other species of the genus. The principal host for all parasitic stages is C. wagneri (Artiodactyla: Tayassuidae). Phylogenetically A. boeroi appears to represent an independent lineage within Amblyomma Koch, 1844. 相似文献
980.
Although there are several species of ferns that are important components of many coastal ecosystems, the adaptations that allow these species to live in salty conditions have been studied only in two Acrostichum species. We have studied the effects of salt on germination, development of the gametophyte and sexual expression of the fern Asplenium marinum, which lives on coastal cliffs of Europe. Cultures at four different levels of salt concentration, 0%, 0.98%, 1.96% and 3.26%, were established for this purpose. Salt caused a significant delay in spore germination, and prevented it completely at high concentrations (3.26%). However, spores were able to recover germination ability after a period of seawater incubation once salinity concentrations decreased. Variable salinity conditions are a typical feature of sea cliffs where halophytes can grow. A salty culture medium also affects the development of the prothalli. Higher salinity of the substrate produced a significant decrease in gametophyte sizes, and affected the development of gametangia as well. Only males were found in a 0.98%-salt medium, and no gametangia were observed in cultures at 1.96%-salt medium. Recovered spores after one and a half month in high salinity concentration, 3.26%, were able, when transplanted to 0%-salt medium, to develop normal sexual prothalli, and this occurred in a shorter time than spores without any prior treatment. A. marinum can be considered as a halophyte fern that is able to germinate and grow in salty conditions. But it takes advantage of rainy periods that cause decrease of salt concentration, which seems to be important in particular for gametangia development and fertilization. 相似文献