Salicylic acid-mediated potentiation of Hsp70 induction correlates with reduced apoptosis in tobacco protoplasts.

BACKGROUND: Elevated temperatures jeopardize plant disease resistance, as mediated by salicylic acid (SA). SA potentiates heat-induced expression of the 70-kDa heat shock protein (Hsp70) in tomato cells. In mammalian cells, Hsp70 suppresses apoptosis. We hypothesized that potentiation of heat-induced Hsp70 by SA contributes to a reduction in apoptosis in tobacco protoplasts. METHODS: Tobacco protoplasts (Nicotiana tabacum) were exposed to SA (70 microM) at normal temperatures or in combination with heat shock. Hsp70/Hsc70 accumulation and phosphatidylserine (PS) exposure, DNA fragmentation, as well as loss of mitochondrial membrane potential were quantified by flow cytometry. RESULTS AND CONCLUSIONS: SA at normal temperatures did not influence Hsp70/Hsc70 accumulation, but were found to induce apoptosis. In contrast, SA in combination with HS potentiated heat-induced Hsp70/Hsc70 accumulation in tobacco protoplasts that correlated negatively with apoptosis, illustrated by decreased PS exposure and DNA fragmentation and enhanced mitochondrial membrane potential. We propose that this correlation supports a possible role for apoptosis suppression by Hsp70 under elevated temperatures during pathogen infection.     

ATP-dependent Ca2+ transport in wheat root plasma membrane vesicles

Plasma membrane preparations of high purity were obtained from roots of dark-grown wheat (Triticum aestivum L. cv. Drabant) by aqueous polymer two-phase partitioning. These preparations mainly contained sealed, right-side-out vesicles (ca 90% exposing the original outside out). By subjecting the preparations to 4 freeze/thaw cycles the proportion of sealed, inside-out (cytoplasmic side out) vesicles increased to ca 30%. Inside-out and right-side-out plasma membrane vesicles were then separated by partitioning the freeze/thawed plasma membranes in another aqueous polymer two-phase system. In this way, highly purified, sealed, inside-out (>60% inside-out) vesicles were isolated and subsequently used for characterization of the Ca²⁺ transport system in the wheat plasma membrane. The capacity for ⁴⁵Ca²⁺ accumulation, nonlatent ATPase activity and proton pumping (the latter two markers for inside-out plasma membrane vesicles) were all enriched in the inside-out vesicle fraction as compared to the right-side-out fraction. This confirms that the ATP-binding site of the ⁴⁵Ca²⁺ transport system, similar to the H⁺-ATPase, is located on the inner cytoplasmic surface of the plant plasma membrane. The ⁴⁵Ca²⁺ uptake was MgATP-dependent with an apparent K_m for ATP of 0.1 mM and a high affinity for Ca²⁺ [K_m(Ca²⁺/EGTA) = 3 μM]. The pH optimum was at 7.4–7.8. ATP was the preferred nucleotide substrate with ITP and GTP giving activities of 30–40% of the ⁴⁵Ca²⁺ uptake seen with ATP. The ⁴⁵Ca²⁺ uptake was stimulated by monovalent cations; K^? and Na⁺ being equally efficient. Vanadate inhibited the ⁴⁵Ca²⁺ accumulation with half-maximal inhibitions at 72, 57 and 2 μM for basal, total (with KCI) and net K⁺-stimulated uptake, respectively. The system was also highly sensitive to erythrosin B with half-maximal inhibition at 25 nM and total inhibition at 1μM. Our results demonstrate the presence of a primary Ca²⁺ transport ATPase in the plasma membrane of wheat roots. The enzyme is likely to be involved in mediating active efflux (ATP-binding sites on the cytoplasmic side) to the plant cell exterior to maintain resting levels of cytoplasmic free Ca²⁺ within the cell.     

Viruses' Life History: Towards a Mechanistic Basis of a Trade-Off between Survival and Reproduction among Phages

Life history theory accounts for variations in many traits involved in the reproduction and survival of living organisms, by determining the constraints leading to trade-offs among these different traits. The main life history traits of phages—viruses that infect bacteria—are the multiplication rate in the host, the survivorship of virions in the external environment, and their mode of transmission. By comparing life history traits of 16 phages infecting the bacteria Escherichia coli, we show that their mortality rate is constant with time and negatively correlated to their multiplication rate in the bacterial host. Even though these viruses do not age, this result is in line with the trade-off between survival and reproduction previously observed in numerous aging organisms. Furthermore, a multiple regression shows that the combined effects of two physical parameters, namely, the capsid thickness and the density of the packaged genome, account for 82% of the variation in the mortality rate. The correlations between life history traits and physical characteristics of virions may provide a mechanistic explanation of this trade-off. The fact that this trade-off is present in this very simple biological situation suggests that it might be a fundamental property of evolving entities produced under constraints. Moreover, such a positive correlation between mortality and multiplication reveals an underexplored trade-off in host–parasite interactions.     

Reduced intimal thickening following alpha(v)beta3 blockade is associated with smooth muscle cell apoptosis

The adhesion integrin alpha(v)beta3 is expressed by both activated endothelial cells (ECs) and smooth muscle cells (SMCs). Peptide and antibody antagonists of alpha(v)beta3 have been shown to block angiogenesis by initiating unscheduled programmed cell death of proliferating ECs. The present study was designed to determine if antagonism of alpha(v)beta3 immediately following balloon injury might similarly lead to programmed cell death among activated SMCs, and thereby inhibit intimal thickening. LM609, a monoclonal antibody antagonist of alpha(v)beta3, was administered locally and/or systemically immediately after balloon angioplasty in a rabbit model of vascular injury. Immunohistochemical studies documented that LM609, even when administered systemically, localized to sites of vascular injury. LM609 administered immediately following balloon injury of the external iliac artery markedly reduced intimal thickening at 2 and 4 wk post-injury. Apoptosis was abundant where balloon injury resulted in expression of alpha(v)beta3. At both 2 and 4 wk, re-endothelialization at the site of balloon injury was not retarded in LM609-treated rabbits versus controls. Thus, blockade of alpha(v)beta3 inhibits intimal thickening when administered immediately following balloon injury. This favorable impact on neointimal thickening is associated with apoptosis of activated SMCs expressing alpha(v)beta3. These findings may explain the reduction in restenosis observed clinically following beta3 integrin blockade.     

Superparasitism and sex ratio in the solitary parasitoidEpidinocarsis lopezi

Highly variable sex ratios are found in the solitary parasitoidEpidinocarsis lopezi, both in the field and in a mass-rearing situation. Superparasitism is one of a number of factors which can influence sex ratios in parasitoid Hymenoptera. We show that superparasitism inE. lopezi is common in the field. Sex allocation decisions when parasitizing unparasitized hosts are not different from those with parasitized hosts; neither does differential mortality occur between the sexes in superparasitized hosts. Therefore superparasitism does not contribute to the variable sex ratio ofE. lopezi. Both the occurrence of superparasitism and the sex produced when ovipositing are shown to be functional forE. lopezi.     

Mutualistic interactions shape global spatial congruence and climatic niche evolution in Neotropical mimetic butterflies

Understanding the mechanisms underlying species distributions and coexistence is both a priority and a challenge for biodiversity hotspots such as the Neotropics. Here, we highlight that Müllerian mimicry, where defended prey species display similar warning signals, is key to the maintenance of biodiversity in the c. 400 species of the Neotropical butterfly tribe Ithomiini (Nymphalidae: Danainae). We show that mimicry drives large-scale spatial association among phenotypically similar species, providing new empirical evidence for the validity of Müller's model at a macroecological scale. Additionally, we show that mimetic interactions drive the evolutionary convergence of species climatic niche, thereby strengthening the co-occurrence of co-mimetic species. This study provides new insights into the importance of mutualistic interactions in shaping both niche evolution and species assemblages at large spatial scales. Critically, in the context of climate change, our results highlight the vulnerability to extinction cascades of such adaptively assembled communities tied by positive interactions.     

Linkage of Wiskott-Aldrich syndrome with three marker loci,DXS426, SYP and TFE3, which map to the Xp11.3–p11.22 region

Linkage analysis was performed in 19 families segregating for the Wiskott-Aldrich syndrome (WAS) and in 1 family with X-linked thrombocytopenia using nine polymorphic DNA markers spanning the interval DXS7-DXS14. The results confirm close linkage of WAS to the DXS7, TIMP, OATL1, DXS255, DXS146, and DXS14 loci and reveal three additional marker loci, DXS426, SYP, and TFE3, to be closely linked to WAS. The linkage data are also consistent with the localization of X-linked thrombocytopenia to the same chromosomal region as WAS and support localization of the WAS gene between the TIMP and DXS 146 loci. However, the data were insufficient for positioning these disease genes with respect to the four marker loci that map within this latter interval. Analysis of recombination events between the marker loci place the TFE3 gene distal to DXS255 and favor the marker loci order Xpter-DXS7-(DXS426, TIMP)-(OATL1, SYP, TFE3)-DXS255-DXS146-DXS14.     

Effect of dark treatment on the starch degradation and the agar quality of cultivated Gracilariopsis lemaneiformis (Rhodophyta,Gracilariales) from Venezuela

The effect of darkness and ammonia on Gracilariopsis lemaneiformis agar yield and quality was studied. Plants were cultivated under controlled conditions in the laboratory and fertilized with ammonia prior to a month storage in the dark. Starch inclusions are known to interfere with the mechanical properties of the isolated agar. The starch content of algal tissue and the activities of the floridean starch phosphorylase and -glucosidase were measured during this storage period as a way to follow the enhancement of starch degradation in the absence of light, and to measure the effect of darkness on the content and quality of the synthesized agar. The agar yield, gel strength, 3,6-anhydrogalactose, sulphate and starch content were considerably affected by this dark treatment. The values obtained reflect a pattern of optimization of agar quality when Gracilariopsis lemaneiformis was stored in the dark. The isolated agar following dark treatment is less contaminated by starch inclusions. This is shown by the improvement in the agar yield and quality, the nutrient status of the plant and the reduction of the starch content.Abbreviations DW: Dry weight - FW: Fresh weight - S: Sulphate - 3,6-AG: 3,6-anhydrogalactose - GS: Gel strenght at 1.5% concentration - CX: Cold extract at 25 °C - A: Autoclaved extract at 121 °C - MW: Molecular weight - PFD: Photon flux density