蚕豆叶片发育与衰老过程中超氧物歧化酶活性与丙二醛含量变化

蚕豆植株叶片随茎节自上而下表现出明显的发育与衰老顺序,可作为衰老特征的是叶绿素和蛋白质含量明显下降。蚕豆叶中SOD活性主要定位于12 000× g离心后所得的上清液和叶绿体组分。衰老叶片的SOD总活性和叶绿体组分的相对活性都有所下降,SOD同工酶谱也发生了改变。O_2~ 产生速率随叶龄增大而稍上升;而MDA含量在叶片外观表现枯黄衰老征兆前就急剧上升。可能因为衰老叶片过氧化氢酶活性大幅度下降与SOD之间的不平衡,致使O_2~ 代谢中间产物累积而引起膜的损伤.     

Biosynthesis of lysosomal hydrolases: their synthesis in bound polysomes and the role of co- and post-translational processing in determining their subcellular distribution

By in vitro translation of mRNA’s isolated from free and membrane-bound polysomes, direct evidence was obtained for the synthesis of two lysosomal hydrolases, β-glucuronidase of the rat preputial gland and cathespin D of mouse spleen, on polysomes bound to rough endoplasmic reticulum (ER) membranes. When the mRNA’s for these two proteins were translated in the presence of microsomal membranes, the in vitro synthesized polypeptides were cotranslationally glycosylated and transferred into the microsomal lumen. Polypeptides synthesized in the absence of microsomal membranes were approximately 2,000 daltons larger than the respective unglycosylated microsomal polypeptides found after short times of labeling in cultured rat liver cells treated with tunicamycin. This strongly suggests that nascent chains of the lysosomal enzymes bear transient amino terminal signals which determine synthesis on bound polysomes and are removed during the cotranslational insertion of the polypeptides into the ER membranes. In the line of cultured rat liver cells used for this work, newly synthesized lysosomal hydrolases showed a dual destination; approximately 60 percent of the microsomal polypeptides detected after short times of labeling were subsequently processed proteolytically to lower molecular weight forms characteristic of the mature enzymes. The remainder was secreted from the cells without further proteolytic processing. As previously observed by other investigations in cultured fibroblasts (A. Gonzalez-Noriega, J.H. Grubbs, V. Talkad, and W.S. Sly, 1980, J Cell Biol. 85: 839-852; A. Hasilik and E.F. Neufeld, 1980, J. Biol. Chem., 255:4937-4945.) the lysosomotropic amine chloroquine prevented the proteolytic maturation of newly synthesized hydrolases and enhanced their section. In addition, unglycosylated hydrolases synthesized in cells treated with tunicamycin were exclusively exported from the cells without undergoing proteolytic processing. These results support the notions that modified sugar residues serve as sorting out signals which address the hydrolases to their lysosomal destination and that final proteolytic cleavage of hydrolase precursors take place within lysosome itself. Structural differences in the carbohydrate chains of intracellular and secreted precursors of cathespin D were detected from their differential sensitivity to digestion with endoglycosidases H and D. These observations suggest that the hydrolases exported into the medium follow the normal secretory route and that some of their oligosaccharides are subject to modifications known to affect many secretory glycoproteins during their passage through the Golgi apparatus.     

Molecular phylogeny of Harpactorinae and Bactrodinae uncovers complex evolution of sticky trap predation in assassin bugs (Heteroptera: Reduviidae)

Sticky trap predation, the use of adhesive substances to trap and capture prey, is an intriguing yet poorly studied predatory strategy. Unique among known sticky trap predators, assassin bugs (Reduviidae) have evolved both exogenous and endogenous sticky trap predatory mechanisms: some trap their prey with sticky plant resins, some scavenge insects entrapped by sticky plant trichomes and others self‐produce sticky secretions. The evolution of these different strategies in assassin bugs is poorly understood due to the lack of comprehensive phylogenies. We reconstruct a phylogeny of Reduviidae (141 taxa; > 5000 bp) focusing on the Harpactorinae and Bactrodinae that engage in sticky trap predation. Ancestral state reconstruction, and temporal and geographical divergence analyses show that sticky trap predation techniques in assassin bugs evolved at least seven times independently since the late Cretaceous: use of sticky plant trichomes evolved as many as four times, resin‐use twice independently and once as a transition from trichome use, and ‘self‐stickiness’ once. Exogenous and endogenous sticky traps first appeared in the Neotropics, with the two exogenous mechanisms (resin and trichome use) subsequently evolving independently in the Old World. This study illustrates, for the first time, the complex evolutionary pattern of sticky trap predation within assassin bugs.     

Cytotoxic and antiviral activities of Colombian medicinal plant extracts of the Euphorbia genus

Forty-seven plant extracts of 10 species of the genus Euphorbia (Euphorbiaceae) used by Colombian traditional healers for the treatment of ulcers, cancers, tumors, warts, and other diseases, were tested in vitro for their potential antitumour (antiproliferative and cytotoxic) and antiherpetic activity. To evaluate the capacity of the extracts to inhibit the lytic activity of herpes simplex virus type 2 (HSV-2) and the reduction of viability of infected or uninfected cell cultures, the end-point titration technique (EPTT) and the MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] colorimetric assay were used, respectively. The therapeutic index of the positive extracts for the antiviral activity was determined by calculating the ratio CC50 (50% cytotoxic concentration) over IC50 (50% inhibitory concentration of the viral effect). Five of the 47 extracts (11%) representing 3 out of 10 Euphorbia species (30%) exhibited antiherpetic action; the highest activity was found in the leaf/stem water-methanol extracts from E. cotinifolia and E. tirucalli. The therapeutic indexes of these two plant species were > 7.1; these extracts exhibited no cytotoxicity. Six extracts (13%) representing 4 plant species (40%) showed cytotoxic activity. The highest cytotoxicity was found in the dichloromethane extract obtained from E. cotinifolia leaves and the CC50 values for the most susceptible cell lines, HEp-2 and CHO, were 35.1 and 18.1 microgram/ml, respectively.     

Modeling temporal and spatial colony-site dynamics in a long-lived seabird

We studied the determinants of colony site dynamics in Audouin's gull, Larus audouinii, breeding in a small archipelago of the western Mediterranean. Data on island occupation were available for a series of 25 years, since first colonization of the archipelago in 1973. Group behavior was studied in relation to the components of dispersal: permanence or abandonment (extinction) on an island previously occupied and permanence or occupation (colonization) of another island. Generalized Linear Mixed Models (GLMMs) were used to identify the relative contribution of each explanatory variable to the probability of colony abandonment. Gulls showed a low probability (3%) of abandoning one of the islands (Grossa I.), especially when the colony was increasing in numbers from time t_i-1 to t_i. However, the probability of abandoning Grossa increased up to 31% when the colony was declining. The probability of island abandonment was very high for all other islands (range 66–99%) when the colony was declining, but much lower (range 36–82%) when it was increasing. Hence, we suggest that island abandonment by Audouin's gull is at least a two-step process. The first step (dispersal of a portion of the colony) probably takes place at random, as an evolutionary load typical of a species evolved in unstable habitats. The second step, a further loss of breeding pairs, seems to feedback on the first loss of members of the colony (public information), likely perceived as a loss of colony quality. Colonization of islands by gulls abandoning Grossa I. was marginally and negatively affected by the density of breeding yellow-legged gulls, a predatory species. Results apply to conservation ecology since they highlight the need to protect not only occupied patches but also those empty at present.     

Peptides of the liver stage antigen-1 (LSA-1) of Plasmodium falciparum bind to human hepatocytes

Synthetic peptides from the liver stage antigen-1 (LSA-1) antigen sequence were used in HepG2 cell and erythrocyte binding assays to identify regions that could be involved in parasite invasion. LSA-1 protein peptides 20630 ((21)INGKIIKNSEKDEIIKSNLRY(40)), 20637 ((157)KEKLQGQQSDSEQERRAY(173)), 20638 ((174)KEKLQEQQSDLEQERLAY(190)) and 20639 (191KEKLQEQQSDLEQERRAY(207)) had high binding activity in HepG2 assays. Were located in immunogenic regions; peptide cell binding was saturable. Peptide 20630 bound specifically to 48kDa HepG2 membrane surface protein. LSA-1 peptides 20630 ((21)INGKIIKNSEKDEIIKSNLRY(40)) and 20633 ((81)DKELTMSNVKNVSQTNFKSLY(100)) showed specific erythrocyte binding activity and inhibited merozoite invasion of erythrocytes in vitro. A monkey serum prepared against LSA-1 20630 peptide analog (CGINGKNIKNAEKPMIIKSNLRGC) inhibited merozoite invasion in vitro. The data suggest LSA-1 "High Activity Binding Peptides" could play a possible role in hepatic cell invasion as well as merozoite invasion of erythrocytes.     

The T-cell-mediated immune response and return rate of fledgling American kestrels are positively correlated with parental clutch size

Life-history theory predicts that parents face a trade-off between the number and viability of the progeny they produce. We found evidence for an apparent trade-off in a free-living population of American kestrels (Falco sparverius), as larger clutches produced more but lighter fledglings. However, while the body mass of fledglings has traditionally been used as a measure of survival prospect, offspring immunocompetence should also play an important role. We thus measured the T-cell-mediated immune response of fledgling kestrels in relation to brood traits and nest-rearing conditions through a cross-fostering experiment. The immune response was positively correlated with the body condition of fledglings, but was also higher in those hatched from five-egg than four-egg clutches. These results were not influenced by other brood traits, nor by current exposure to stressors and infectious agents, as measured by serological variables. Such ability to resist pathogens may account for why the probability of offspring returning to the study area in subsequent years, when controlling for brood size, was higher for five-egg than four-egg clutches. These results suggest an optimal clutch size through maternal effects on offspring immunocompetence rather than a trade-off between the number and quality of the offspring.     

Molecular evolution of P transposable elements in the genus Drosophila. III. The melanogaster species group

Phylogenetic relationships were determined for 76 partial P-element sequences from 14 species of the melanogaster species group within the Drosophila subgenus Sophophora. These results are examined in the context of the phylogeny of the species from which the sequences were isolated. Sequences from the P-element family fall into distinct subfamilies, or clades, which are often characteristic for particular species subgroups. When examined locally among closely related species, the evolution of P elements is characterized by vertical transmission, whereby the P-element phylogeny traces the species phylogeny. On a broader scale, however, the P-element phylogeny is not congruent with the species phylogeny. One feature of P-element evolution in the melanogaster group is the presence of more than one P-element subfamily, differing by as much as 36%, in the genomes of some species. Thus, P elements from several individual species are not monophyletic, and a likely explanation for the incongruence between P-element and species phylogenies is provided by the comparison of paralogous sequences. In certain instances, horizontal transfer seems to be a valid alternative explanation for lack of congruence between species and P-element phylogenies. The canonical P-element subfamily, which represents the active, autonomous transposable element, is restricted to D. melanogaster. Thus, its origin clearly lies outside of the melanogaster species group, consistent with the earlier conclusion of recent horizontal transfer.      

Noisy-threshold control of cell death

Background  

Cellular responses to death-promoting stimuli typically proceed through a differentiated multistage process, involving a lag phase, extensive death, and potential adaptation. Deregulation of this chain of events is at the root of many diseases. Improper adaptation is particularly important because it allows cell sub-populations to survive even in the continuous presence of death conditions, which results, among others, in the eventual failure of many targeted anticancer therapies.