Variability in space and time: contrasting fruit distribution patterns in the deceptive orchid Orchis militaris

• In angiosperms, a decrease in fruit production towards the apex of individual inflorescences is usually observed. Orchids are thought to be primarily pollination‐limited species, and non‐uniform pollination could cause this decrease pattern in several species. Fruit production was investigated in relation to flower position and floral display size in Orchis militaris (Orchidaceae), a deceptive species.
• Over 2 years, eight populations of O. militaris were studied and fruit position along the inflorescence was recorded. Generalised linear models were performed to examine the effect of population, year, flower position and floral display size on fruit production.
• The dominant pattern was characterised by a higher fruit set in the middle part of the inflorescence (parabolic pattern). A non‐directional pattern of fruit production was also detected in some populations. Within a given population, patterns were generally consistent among years. In one of the two study years and in one of the eight populations specifically, the proximal‐to‐distal decrease in fruit production was dramatic in plants with a large floral display but weak or absent in small displays.
• Our study demonstrates the intraspecific diversity of fruit distribution patterns in O. militaris. Non‐uniform pollination along the inflorescence is likely to be responsible for the parabolic pattern, while irregular visitation could explain the non‐directional pattern of fruit production. Pattern variation among years and between populations could arise from spatiotemporal variation in pollinator assemblages. Resource competition effects could explain the interaction effect between display size and flower position.

     

Fluorescence-based melting assays for studying quadruplex ligands

The telomeric G-rich single-stranded DNA can adopt in vitro an intramolecular quadruplex structure, which has been shown to directly inhibit telomerase activity. The reactivation of this enzyme in immortalized and most cancer cells suggests that telomeres and telomerase are relevant targets in oncology, and telomere ligands and telomerase inhibitors have been proposed as new potential anticancer agents. In this paper, we have analysed the FRET method used to measure the stabilization and selectivity of quadruplex ligands towards the human telomeric G-quadruplex. The stabilization value depends on the nature of the fluorescent tags, the incubation buffer, and the method chosen for T(m) calculation, complicating a direct comparison of the results obtained by different laboratories.     

Bicyclo[2.2.2]octyl esters of dialkylamino acids as antiprotozoals

A couple of bicyclo[2.2.2]octyl esters of 2-dialkylaminoacetic acids were prepared. Their antiplasmodial and antitrypanosomal activities against Trypanosoma brucei rhodesiense (STIB 900) and the K(1) strain of Plasmodium falciparum (resistant to chloroquine and pyrimethamine) were determined using microplate assays. Structure-activity relationships were discussed. The antiprotozoal activities were remarkably increased by insertion of a second basic centre. The selectivity indices of the most active compounds are superior in the bicyclo-octane series.     

Biodistribution studies of protein cage nanoparticles demonstrate broad tissue distribution and rapid clearance in vivo

Protein cage nanoparticles have the potential to serve as multifunctional cell targeted, imaging and therapeutic platforms for broad applications in medicine. However, before they find applications in medicine, their biocompatibility in vivo needs to be demonstrated. We provide here baseline biodistribution information of two different spherical protein cage nanoplatforms, the 28 nm viral Cowpea chlorotic mottle virus (CCMV) and the 12 nm heat shock protein (Hsp) cage. In naive and immunized mice both nanoplatforms show similar broad distribution and movement throughout most tissues and organs, rapid excretion, the absence of long-term persistence within mice tissue and organs, and no overt toxicity after a single injection. These results suggest that protein cage based nanoparticles may serve as safe, biocompatible, nanoplatforms for applications in medicine.     

Proteomics of proteasome complexes and ubiquitinated proteins

Ubiquitin-proteasome-mediated protein degradation is central to the regulation of many important biological processes, including cell cycle progression, apoptosis and DNA repair. Recognition and degradation of ubiquitinated substrates by the 26S proteasome is tightly regulated to maintain normal cell growth. Disruption of the proteasomal degradation pathway has been implicated in a wide range of human diseases. Although the ubiquitin-proteasome system has been intensively investigated, many key questions remain unanswered in regard to its components and regulation of its activities. A key step towards a full understanding of the pathway is to investigate the proteasome complex subunit composition, heterogeneity, post-translational modifications, assembly, proteasome interaction networks and degradation substrates. Mass spectrometry-based proteomic approaches have been successfully applied for unraveling the details of the proteasome complexes and their substrates in an unprecedented fashion. An overview of the current knowledge of the proteasomal degradation pathway based on mass spectrometry approaches is presented.     

Perturbations of malate accumulation and the endogenous rhythms of gas exchange in the Crassulacean acid metabolism plant<Emphasis Type="Italic"> Kalanchoë daigremontiana</Emphasis>: testing the tonoplast-as-oscillator model

In continuous light, leaves of the Crassulacean acid metabolism (CAM) plant Kalanchoë daigremontiana Hamet et Perrier exhibit a circadian rhythm of CO₂ uptake, stomatal conductance and leaf-internal CO₂ pressure. According to a current quantitative model of CAM, the pacemaking mechanism involves periodic turgor-related tension and relaxation of the tonoplast, which determines the direction of the net flux of malate between the vacuole and the cytoplasm. Cytoplasmic malate, in turn, through its inhibitory effect on phosphoenolpyruvate carboxylase, controls the rate of CO₂ uptake. According to this mechanism, when the accumulation of malate is disrupted by removing CO₂ from the ambient air, the induction of a phase delay with respect to an unperturbed control plant is expected. First, using the mathematical model, such phase delays were observed in numerical simulations of three scenarios of CO₂ removal: (i) starting at a trough of CO₂ uptake, lasting for about half a cycle (ca. 12 h in vivo); (ii) with the identical starting phase, but lasting for 1.5 cycles (ca. 36 h); and (iii) starting while CO₂ increases, lasting for half a cycle again. Applying the same protocols to leaves of K. daigremontiana in vivo did not induce the predicted phase shifts, i.e. after the end of the CO₂ removal the perturbed rhythm adopted nearly the same phase as that of the control plant. Second, when leaves were exposed to a nitrogen atmosphere for three nights prior to onset of continuous light to prevent malate accumulation, a small, 4-h phase advance was observed instead of a delay, again contrary to the model-based expectations. Hence, vacuolar malic acid accumulation is ruled out as the central pacemaking process. This observation is in line with our earlier suggestion [T.P. Wyka, U. Lüttge (2003) J Exp Bot 54:1471–1479] that in extended continuous light, CO₂ uptake switches gradually from a CAM-like to a C3-like mechanism, with oscillations of the two CO₂ uptake systems being tightly coordinated. It appears that the circadian rhythm of gas exchange in this CAM plant emerges from one or several devices that are capable of generating temporal information in a robust manner, i.e. they are protected from even severe metabolic perturbations.Abbreviations CAM Crassulacean acid metabolism - c_ia Ratio of mesophyll CO₂ concentration to external CO₂ concentration - J_C Rate of carbon dioxide uptake - J_W Transpiration rate - g_W Stomatal conductance - LL Continuous light conditions - PEPC Phosphoenolpyruvate carboxylase - Rubisco d-Ribulose-1,5-bisphosphatecarboxylase/oxygenase - Effective quantum yield of photosystem II     

The mechanisms of refilling of xylem conduits and bleeding of tall birch during spring

Seasonal variations in osmolality and components of xylem sap in tall birch trees were determined using several techniques. Xylem sap was extracted from branch and trunk sections of 58 trees using the very rapid gas bubble-based jet-discharge method. The 5-cm long wood pieces were taken at short intervals over the entire tree height. The data show that large biphasic osmolality gradients temporarily exist within the conducting xylem conduits during leaf emergence (up to 272 mosmol x kg(-1) at the apex). These gradients (arising mainly from glucose and fructose) were clearly held within the xylem conduit as demonstrated by (1)H NMR imaging of intact twigs. Refilling experiments with benzene, sucrose infusion, electron and light microscopy, as well as (1)H NMR chemical shift microimaging provided evidence that the xylem of birch represents a compartment confined by solute-reflecting barriers (radial: lipid linings/lipid bodies; axial: presumably air-filled spaces). These features allow transformation of osmolality gradients into osmotic pressure gradients. Refilling of the xylem occurs by a dual mechanism: from the base (by root pressure) and from the top (by hydrostatic pressure generated by xylem-bound osmotic pressure). The generation of osmotic pressure gradients was accompanied by bleeding. Bleeding could be observed at a height of up to 21 m. Bleeding rates measured at a given height decreased exponentially with time. Evidence is presented that the driving force for bleeding is the weight of the static water columns above the bleeding point. The pressure exerted by the water columns and the bleeding volume depend on the water-filling status of (communicating) vessels.     

Warm Springs,Early Lay Dates,and Double Brooding in a North American Migratory Songbird,the Black-Throated Blue Warbler

Numerous studies have correlated the advancement of lay date in birds with warming climate trends, yet the fitness effects associated with this phenological response have been examined in only a small number of species. Most of these species–primarily insectivorous cavity nesters in Europe–exhibit fitness declines associated with increasing asynchrony with prey. Here, we use 25 years of demographic data, collected from 1986 to 2010, to examine the effects of spring temperature on breeding initiation date, double brooding, and annual fecundity in a Nearctic - Neotropical migratory songbird, the black-throated blue warbler (Setophaga caerulescens). Data were collected from birds breeding at the Hubbard Brook Experimental Forest, New Hampshire, USA, where long-term trends toward warmer springs have been recorded. We found that black-throated blue warblers initiated breeding earlier in warmer springs, that early breeders were more likely to attempt a second brood than those starting later in the season, and that double brooding and lay date were linked to higher annual fecundity. Accordingly, we found selection favored earlier breeding in most years. However, in contrast to studies of several other long-distance migratory species in Europe, this selection pressure was not stronger in warmer springs, indicating that these warblers were able to adjust mean lay date appropriately to substantial inter-annual variation in spring temperature. Our results suggest that this North American migratory songbird might not experience the same fecundity declines as songbirds that are unable to adjust their timing of breeding in pace with spring temperatures.