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221.
Fernando Rodrigues da Silva Mário Almeida‐Neto Vitor Hugo Mendonça do Prado Célio Fernando Baptista Haddad Denise de Cerqueira Rossa‐Feres 《Journal of Biogeography》2012,39(9):1720-1732
Aim The diversity of reproductive modes among amphibians constitutes a striking example of how differences in the biology of species provide important explanations for species distribution patterns on a broad scale. We hypothesize that sites with a higher humidity level will support more modes of reproduction than drier sites and will consequently exhibit a higher phylogenetic diversity. Furthermore, if there is a gradient in the tolerance of reproductive modes to desiccation, there will be a nested pattern in the composition of reproductive modes among sites. Location Twenty‐seven forest sites in the Brazilian Atlantic Forest. Methods Through a path analysis approach, we evaluated the direct and indirect effects of the humidity level on the number of reproductive modes, as well as the relative importance of both variables on amphibian phylogenetic diversity. A nestedness analysis was used to quantify the extent to which the compositions of both species and reproductive modes in drier sites correspond to subsets of those in sites with higher annual precipitation. Results We found that the reproductive modes present in drier sites are non‐random subsets of those present in sites with higher humidity levels. Because reproductive modes are phylogenetically conserved among amphibians, sites with a greater number of reproductive modes supported greater phylogenetic diversity. Sites with high precipitation throughout the year provided suitable environmental conditions for a larger number of reproductive modes, whereas sites with low precipitation and typical seasonal climates supported only those reproductive modes specialized to resist desiccation. Main conclusions Our results show that humidity‐related variables are key environmental factors related to both the richness of reproductive modes and phylogenetic diversity. Our results support the hypothesis that the higher phylogenetic diversity found in moister sites reflects differences in the tolerance to desiccation among different reproductive modes. Given that reproductive modes are associated with susceptibility to desiccation, their incorporation into explanatory models may trigger a significant advance in the understanding of the mechanisms regulating the species richness and composition of amphibian communities. 相似文献
222.
223.
Nitric oxide (NO) controls diverse functions in many cells and organs of animals. It is also produced in plants and has a variety of effects, but little is known about their underlying mechanisms. In the present study, we have discovered a role for NO in the regulation of pollen tube growth, a fast tip-growing cellular system. Pollen tubes must be precisely oriented inside the anatomically complex female ovary in order to deliver sperm. We hypothesized that NO could play a role in this guidance and tested this hypothesis by challenging the growth of pollen tubes with an external NO point source. When a critical concentration was sensed, the growth rate was reduced and the growth axis underwent a subsequent sharp reorientation, after which normal growth was attained. This response was abrogated in the presence of the NO scavenger CPTIO and affected by drugs interfering in the cGMP signaling pathway. The sensitivity threshold of the response was significantly augmented by sildenafil citrate (SC), an inhibitor of cGMP-specific phosphodiesterases in animals. NO distribution inside pollen tubes was investigated using DAF2-DA and was shown to occur mostly in peroxisomes. Peroxisomes are normally excluded from the tip of pollen tubes and little if any NO is found in the cytosol of that region. Our data indicate that the rate and orientation of pollen tube growth is regulated by NO levels at the pollen tube tip and suggest that this NO function is mediated by cGMP. 相似文献
224.
Prado SR Cechinel-Filho V Campos-Buzzi F Corrêa R Cadena SM de Oliveira MB 《Zeitschrift für Naturforschung. C, Journal of biosciences》2004,59(9-10):663-672
Cyclic imides such as succinimides, maleimides, glutarimides, phthalimides and their derivatives contain an imide ring and a general structure -CO-N(R)-CO- that confers hydrophobicity and neutral characteristic. A diversity of biological activities and pharmaceutical uses have been attributed to them, such as antibacterial, antifungal, antinociceptive, anticonvulsant, antitumor. In spite of these activities, much of their action mechanisms at molecular and cellular levels remain to be elucidated. We now show the effects of several related cyclic imides: maleimides (S2, S2.1, S2.2, S3), glutarimides (S4, S5, S6), 4-aminoantipyrine derivatives (L1, F1, AL1, F1.14, F1.2) and sulfonated succinimides (RO1, FA, FE, FD, MC, DMC) on isolated rat liver mitochondria, B16-F10 melanoma cell line, peritoneal macrophages and different bacterial streams. The effects on mitochondrial respiratory parameters, cell viability and antibacterial activity were also evaluated. The results indicated that S3, S5 and S6 caused an increased oxygen consumption in the presence of ADP (state III) or its absence (state IV), while all other compounds decreased those parameters at different degrees of inhibition. All the compounds decreased the respiratory control coefficient (RCC). Loss of cell viability of peritoneal macrophages and the B16-F10 cell line was observed, L1 and S2.1 being more effective. S1, S2, S3, L1 and F1 compounds showed antibacterial activity at experimental concentrations. 相似文献
225.
Teixeira Ddo C Rocha SR de Santos MA Mariano AG Li WB Monteiro PB 《Current microbiology》2004,49(6):396-399
The genome sequence of the pathogen Xylella fastidiosa Citrus Variegated Chlorosis (CVC) strain 9a5c has revealed many genes related to pathogenicity mechanisms and virulence determinants. However, strain 9a5c is resistant to genetic transformation, impairing mutant production for the analysis of pathogenicity mechanisms and virulence determinants of this fastidious phytopathogen. By screening different strains, we found out that cloned strains J1a12, B111, and S11400, all isolated from citrus trees affected by CVC, are amenable to transformation, and J1a12 has been used as a model strain in a functional genomics program supported by FAPESP (São Paulo State Research Foundation). However, we have found that strain J1a12, unlike strains 9a5c and B111, was incapable of inducing CVC symptoms when inoculated in citrus plants. We have now determined that strain B111 is an appropriate candidate for post-genome studies of the CVC strain of X. fastidiosa. 相似文献
226.
Prado MA Alves-Silva J Magalhães AC Prado VF Linden R Martins VR Brentani RR 《Journal of neurochemistry》2004,88(4):769-781
The glycosylphosphatidylinositol (GPI)-anchored cellular prion protein (PrPc) has a fundamental role in prion diseases. Intracellular trafficking of PrPc is important in the generation of protease resistant PrP species but little is known of how endocytosis affects PrPc function. Here, we discuss recent experiments that have illuminated how PrPc is internalized and what are the possible destinations taken by the protein. Contrary to what would be expected for a GPI-anchored protein there is increasing evidence that clathrin-mediated endocytosis and classical endocytic organelles participate in PrPc trafficking. Moreover, the N-terminal domain of PrPc may be involved in sorting events that can direct the protein during its intracellular journey. Indeed, the concept that the GPI-anchor determines PrPc trafficking has been challenged. Cellular signaling can be triggered or be regulated by PrPc and we suggest that endocytosis of PrPc may influence signaling in several ways. Definition of the processes that participate in PrPc endocytosis and intracellular trafficking can have a major impact on our understanding of the mechanisms involved in PrPc function and conversion to protease resistant conformations. 相似文献
227.
228.
The impacts of forest fragmentation on the pteridophyte communities of the Una region of Bahia, Brazil, were investigated
by comparing species richness and ensemble diversity among areas of large forest fragments (>900 ha), small forest fragments
(<100 ha), and landscape matrix. We inventoried the pteridophytes below 1 m in height in interiors of small fragments, interiors
of large fragments (control areas), edges of fragments, edges of continuous forest, capoeiras (initial stages of forest regeneration) and cabrucas (cocoa plantations). All ferns were collected following the plot method (plots of 120×10 m, each). Sampling units were established
in the six main ecotypes of the Una region. These units were allocated within three sampling blocks of 5 per 5 km, which were
chosen in order to include the largest forest patches that still remain. Results suggest that fragmentation has a negative
impact on species richness at the matrix and the edges of forest remnants. A similar negative matrix end edge effect is reported
for diversity of those sites measured by the α Log-series Index. However, small forest fragments have pteridophyte species
richness and diversity rates similar to large ones so they should be considered of utmost importance to the conservation of
forest-related species in the region. 相似文献
229.
María Angélica?DamascosEmail author Carlos Henrique B. A.?Prado Ana Aydeé?Ladio Maria Angélica?Arribere Sergio Ribeiro?Guevara 《Plant Ecology》2005,181(1):1-8
Previous studies analyzed the importance of old leaves conservancy for wintergreen species plant growth only after early spring
old leaves elimination. However, carbon and nutrient resources for growth could have already been translocated from old leaves
to shoots during autumn. In this work, the effect of old leaves absence on the leaf mass per area (LMA, g m−2) and nutrient concentration of new spring leaves, shoot growth, and flowering was studied in Aristotelia chilensis, an Andean Patagonic woody wintergreen species of Argentina. Plants were studied after autumn defoliation (AD) or late winter
defoliation (WD) and results were compared to those of undamaged control plants (CO). The new leaves LMA and mineral nutrient
(N, P, K, and Mg) concentration values did not decrease in AD or WD compared to CO plants. Conversely, CO plants showed higher
flowering intensity and shoot lengthening compared to AD or WD plants. There were not remarkable differences regarding the
defoliation time, though non-flowering shoots grew in a lesser degree than the flowering shoots in WD plants. It was concluded
that A. chilensis old leaves cohort is an important source to shoot growth and flowering but their absence does not affect the new leaves structure
or nutritional status from early spring in either AD or in WD plants. New leaves formation probably is guaranteed by resources
(carbon and nutrients) previously stored in stems or even in the buds containing the preformed leaves since March, by the
end of summer. Provided the availability of complete resources for the new leaf flush independently of the old leaves A. chilensis would restore the carbon balance as soon as possible to resume the growth of heterotrophic tissues at normal rates. Endogenous
response to counterbalance the old leaves absence on non-flowering shoots was more effective when there was greater lag time
between defoliation and shoot growth resume. Flowering and non-flowering shoots compete for the available resources when A. chilensis have not yet expanded leaves and shoots supporting reproductive structures were stronger sinks compared to non-flowering
shoots in WD plants. 相似文献
230.
Activation of the hypothalamus-pituitary-adrenal axis plays a major role in the suppression of the immune system. We have investigated the effects of repetitive stress on Wistar rats infected with the Y strain of Trypanosoma cruzi and a control group that underwent stressor stimuli by exposure to ether vapor for one minute twice a day. Repetitive stress resulted in an elevated number of circulating parasites accompanies by deep tissue disorganization, and cardiac histopathological alterations. The infected and stressed group displayed a decrease in body weight, and an increased parasite burden in heart tissue, and adrenal glands. Histological analysis of the heart also showed a moderate to severe diffused mononuclear inflammatory process. These results suggest that repetitive stress could be considered an important factor during development of experimental Chagas' disease, enhancing pathogenesis through disturbance of the host's immune system. 相似文献