Responses to simulated herbivory and water stress in two tropical C4 grasses

Summary The African grass Hyparrhenia rufa has established itself successfully in South American savannas (Llanos) and displaced dominant native grasses such as Trachypogon plumosus from the wetter and more fertile habitats. Several ecophysiological traits have been related to the higher competitive capacity of H. rufa. To further analyze the behavior of both species, their growth, biomass allocation, physiological and architectural responses to defoliation and water stress were compared under controlled conditions. Although total, aerial and underground biomass decreased under defoliation in both grasses, increases in clipped-leaf biomass and area compensated for defoliation in H. rufa but not in T. plumosus. This difference was due mainly to a higher proportion of assimilates being directed to leaf and tiller production and a higher leaf growth rate in the African grass as compared to T. plumosus, which showed incrased senescence under frequent defoliation. In both species, water stress ameliorated the effects of defoliation. The ability to compensate for defoliated biomass in H. rufa is possibly related to its long coevolution with large herbivores in its original African habitat and is apparently one of the causes of its success in Neotropical savannas.     

Production in Escherichia coli of a biologically active subfragment of von Willebrand factor corresponding to the platelet glycoprotein Ib, collagen and heparin binding domains

A full-length cDNA for vWF has been cloned from a human lung cDNA library and a fragment of this cDNA has been modified to allow its expression in E. coli. This fragment, which corresponds to Val 449-Asn 730 of vWF and includes the GPIb-binding domain and binding sites for collagen and heparin, was subcloned into an expression vector containing an inducible lambda PL promoter. On induction, the expressed recombinant vWF subfragment migrated with a mol wt of around 38,000 after SDS-PAGE. It was identified as a vWF fragment by Western blotting using either a polyclonal or a monoclonal antibody which inhibits the binding of vWF to GPIb. Following solubilization in urea, the bacterial extract inhibited ristocetin-induced platelet aggregation and bound to ristocetin-treated platelets, to collagen and to heparin.     

Epidemiology of training injuries in amateur taekwondo athletes: a retrospective cohort study

The objectives of this study were to estimate the incidence and describe the pattern and severity of training injuries in taekwondo, and to compare pattern and severity of training injuries with competition injuries. One hundred and fifty-two active Australian amateur taekwondo athletes, aged 12 years or over, completed an online survey comprising questions on training exposure and injury history over the preceding 12 months. The main outcome measures were: overall injury incidence rate per athlete-year; training injury incidence rate per athlete-year, per 1000 athlete-training-sessions, and per 1000 athlete-hours of training; injury severity; and injury proportions by anatomical region and by type of injury. Injury incidence rates were calculated with 95% confidence intervals using standard methods, while injury proportions were compared using Fisher''s exact test. The vast majority (81.5%) of taekwondo injuries in an average athlete-year occurred during training. The training injury incidence rate was estimated to be 1.6 (95% CI: 1.4, 1.9) per athlete-year, 11.8 (95% CI: 10.4, 13.4) per 1000 athlete-training-sessions, and 7.0 (95% CI: 6.1, 7.9) per 1000 athlete-hours of training. Among athletes with five or fewer injuries, the severity and injury pattern of training injuries were, by and large, the same as for competition injuries. Approximately sixty percent (60.3%) of training injuries required treatment by a health professional. Considering the burden of training injuries exceeds that of competition injuries, taekwondo governing bodies and stakeholders are encouraged to devote more efforts towards the identification of risk factors for, and prevention of, training injuries in the sport of taekwondo.     

Using functional groups to investigate community response to environmental changes: two grassland case studies

Functional groups (FG) are an useful generalization to investigate environmental change effects on biotic communities. Assigning species to FGs is a contextual task and carries an arbitrary element, regardless of whether the grouping is obtained a priori or by sophisticated numerical methods. Using two grassland community case studies, we show that even simple FG allocation based on growth form, architecture and longevity (plants and mosses), or foraging characteristics (above-ground invertebrates) can be useful to increase our understanding of community processes. For example, the sensitivity of organisms to climate change increases with trophic rank and is higher in disturbed than in undisturbed communities. Complexity of interaction webs (in terms of web connectance), however, is larger in undisturbed than in disturbed communities. A significant and important relationship is likely to exist between anthropogenic disturbances, community complexity and the ecosystem effects of climate change. Trophic interactions may be disrupted much easier by climate changes in disturbed than in undisturbed communities where complexity may be buffering these effects.     

Open channel block by Ca2+ underlies the voltage dependence of drosophila TRPL channel

The light-activated channels of Drosophila photoreceptors transient receptor potential (TRP) and TRP-like (TRPL) show voltage-dependent conductance during illumination. Recent studies implied that mammalian members of the TRP family, which belong to the TRPV and TRPM subfamilies, are intrinsically voltage-gated channels. However, it is unclear whether the Drosophila TRPs, which belong to the TRPC subfamily, share the same voltage-dependent gating mechanism. Exploring the voltage dependence of Drosophila TRPL expressed in S2 cells, we found that the voltage dependence of this channel is not an intrinsic property since it became linear upon removal of divalent cations. We further found that Ca(2+) blocked TRPL in a voltage-dependent manner by an open channel block mechanism, which determines the frequency of channel openings and constitutes the sole parameter that underlies its voltage dependence. Whole cell recordings from a Drosophila mutant expressing only TRPL indicated that Ca(2+) block also accounts for the voltage dependence of the native TRPL channels. The open channel block by Ca(2+) that we characterized is a useful mechanism to improve the signal to noise ratio of the response to intense light when virtually all the large conductance TRPL channels are blocked and only the low conductance TRP channels with lower Ca(2+) affinity are active.     

Neural networks applied to the prediction of fed-batch fermentation kinetics of Bacillus thuringiensis

This paper proposes using a new recurrent neural network model (RNNM) to predict and control fed batch fermentations of Bacillus thuringiensis. The control variables are the limiting substrate and the feeding conditions. The multi-input multi-output RNNM proposed has twelve inputs, seven outputs, nineteen neurons in the hidden layer, and global and local feedbacks. The weight update learning algorithm designed is a version of the well known backpropagation through time algorithm directed to the RNNM learning. The error approximation for the last epoch of learning is 2% and the total learning time is 51 epochs, where the size of an epoch is 162 iterations. The RNNM generalization was carried out reproducing a B. thuringiensis fermentation not included in the learning process. It attains an error approximation of 1.8%.     

Generation of ligand-receptor alliances by "SEA" module-mediated cleavage of membrane-associated mucin proteins

A mechanism is described whereby one and the same gene can encode both a receptor protein as well as its specific ligand. Generation of this receptor-ligand partnership is effected by proteolytic cleavage within a specific module located in a membrane resident protein. It is postulated here that the "SEA" module, found in a number of heavily O-linked glycosylated membrane-associated proteins, serves as a site for proteolytic cleavage. The subunits generated by proteolytic cleavage of the SEA module reassociate, and can subsequently elicit a signaling cascade. We hypothesize that all membrane resident proteins containing such a "SEA" module will undergo cleavage, thereby generating a receptor-ligand alliance. This requires that the protein subunits resulting from the proteolytic cleavage reassociate with each other in a highly specific fashion. The same SEA module that serves as the site for proteolytic cleavage, probably also contains the binding sites for reassociation of the resultant two subunits. More than one type of module can function as a site for proteolytic cleavage; this can occur not only in one-pass membrane proteins but also in 7-transmembrane proteins and other membrane-associated proteins. The proposal presented here is likely to have significant practical consequences. It could well lead to the rational design and identification of molecules that, by binding to one of the cleaved partners, will act either as agonists or antagonists, alter signal transduction and, hence, cellular behavior.     

Variations among cell lines in the synthesis of sphingolipids in de novo and recycling pathways

There are several pathways for the incorporation of sugars into glycosphingolipids (GSL). Sugars can be added to ceramide that contains sphinganine (dihydrosphingosine) synthesized de novo (pathway 1), to ceramide synthesized from sphingoid bases produced by hydrolysis of sphingolipids (pathway 2), and into GSL recycling from the endosomal pathway through the Golgi (pathway 3). We reported previously the surprising observation that SW13 cells, a human adrenal carcinoma cell line, synthesize most of their GSL in pathway 2. We now present data on the synthesis of GSL in four additional cell lines. Approximately 90% of sugar incorporation took place in pathway 2, and 10% or less in pathway 1, in human foreskin fibroblasts and NB41A3 neuroblastoma cells. In contrast, approximately 50-90% of sugar incorporation took place in pathway 1 in C2C12 myoblasts. The C2C12 cells divide more rapidly and synthesize 10-14 times as much GSL as the other three cell lines. In C6 glioma cells, approximately 30% of sugar incorporation occurred in pathway 1 and 60% in pathway 2. There was no relation between the utilization of pathways for GSL and sphingomyelin synthesis in foreskin fibroblasts and C2C12 cells. In both cells pathways 1 and 2 each accounted for 50% of incorporation of choline into sphingomyelin. In five of the six cell lines that we have studied, most GSL synthesis takes place in pathway 2. We suggest that when the need for synthesis is relatively low, as in slowly dividing cells, GSL are synthesized predominantly from sphingoid bases salvaged from the hydrolytic pathway. When cells are dividing more rapidly, the need for increased synthesis is met by upregulating the de novo pathway.