Endothelial plasminogen activator inhibitor (PAI): a new member of the Serpin gene family.

A human endothelial cDNA expression library, based on the Escherichia coli plasmid pUC9, was screened with a heterologous antibody raised against purified bovine aortic endothelial plasminogen activator inhibitor (PAI). A synthetic oligonucleotide, derived from a partial PAI cDNA expression clone, was used to select a full-length PAI cDNA, the size of which coincides with the length of PAI mRNA (approximately 2350 nucleotides) as determined by Northern blot analysis. The authenticity of full-length PAI cDNA is demonstrated by the expression of biologically active PAI both in lysates of transformed E. coli cells and in conditioned media of mouse Ltk- cells, transfected with PAI cDNA inserted into vector pSV2. Analysis of the de novo synthesized anti-plasminogen activator activity, employing reverse fibrin autography, shows that transfected mouse Ltk- cells synthesize a polypeptide with a mol. wt identical to that of the native PAI glycoprotein (Mr 52,000), whereas in E. coli an unglycosylated, active product with a mol. wt of 43,000 is made. The amino acid sequence, derived from the determined nucleotide sequence, shows that pre-PAI consists of 402 amino acids. It is proposed that the mature PAI is preceded by a signal peptide of 23 amino acid residues. The amino acid sequence of mature PAI includes three potential asparagine-linked glycosylation sites and lacks cysteine residues. The predicted amino acid sequence reveals significant homology with members of the serine protease inhibitor (Serpin) family, e.g. alpha 1-proteinase inhibitor and antithrombin III.(ABSTRACT TRUNCATED AT 250 WORDS)     

Evidence for a significant contribution by peroxidase-mediated O2 uptake to root respiration of Brachypodium pinnatum

This study describes the O₂ uptake characteristics of intact roots of Brachypodium pinnatum. In the presence of 25 mM salicylhydroxamic acid (SHAM), concentrations of KCN below 3.5 νM had no effect on the rate of root respiration, whereas in the absence of 25 mM SHAM a significant inhibition of approx. 18% was observed. This indicates that an O₂-consuming reaction, not associated with the cytochrome pathway, the alternative pathway or the “residual component”, operates in the absence of any inhibitors in roots of B. pinnatum. We demonstrate here that this fourth O₂-consuming reaction is mediated by a peroxidase. A peroxidase which catalyzed O₂ reduction in the presence of NADH was readily washed from the roots of B. pinnatum. This peroxidase was stimulated by 5 mM SHAM, whereas ascorbic acid, catalase, catechol, gentisic acid, low concentrations potassium cyanide (3.5 μM), sodium azide, sodium sulfide, superoxide dismutase and high concentrations SHAM (25 mM) inhibited this reaction. Except for high concentrations of SHAM and concentrations of KCN higher than approx. 3.5 μM, these effectors could not be used to inhibit the peroxidase-mediated O₂ uptake in intact roots of B. pinnatum. Concentrations of SHAM below 10 mM stimulated O₂ uptake up to 15% of the control rate, depending on concentration, whereas 25 mM SHAM inhibited O₂ uptake by 35%. The stimulation at low concentrations resulted from a SHAM-stimulated peroxidase activity, whereas 25 mM SHAM completely inhibited both the peroxidase-mediated O₂ uptake and the activity of the alternative pathway. A method is presented for determining the relative contributions of each of the four O₂-consuming reactions, i.e. the cytochrome pathway, the alternative pathway, the “residual component” and the peroxidase-mediated O₂ uptake. The peroxidase-mediated O₂ uptake contributed 21% to the total rate of oxygen uptake in roots of B. pinnatum, the cytochrome pathway contributed 41%, the alternative pathway 14% and the “residual component” 24%.     

Rainfall-driven sex-ratio genes in African buffalo suggested by correlations between Y-chromosomal haplotype frequencies and foetal sex ratio

Background  

The Y-chromosomal diversity in the African buffalo (Syncerus caffer) population of Kruger National Park (KNP) is characterized by rainfall-driven haplotype frequency shifts between year cohorts. Stable Y-chromosomal polymorphism is difficult to reconcile with haplotype frequency variations without assuming frequency-dependent selection or specific interactions in the population dynamics of X- and Y-chromosomal genes, since otherwise the fittest haplotype would inevitably sweep to fixation. Stable Y-chromosomal polymorphism due one of these factors only seems possible when there are Y-chromosomal distorters of an equal sex ratio, which act by negatively affecting X-gametes, or Y-chromosomal suppressors of a female-biased sex ratio. These sex-ratio (SR) genes modify (suppress) gamete transmission in their own favour at a fitness cost, allowing for stable polymorphism.     

Phosphorus-fertilisation has differential effects on leaf growth and photosynthetic capacity of Arachis hypogaea L.

Plant and Soil - The objectives of this study were to assess how Arachis hypogaea L. (peanut or groundnut) responds to different P supplies in terms of growth and photosynthesis, and to determine...     

A cool spot in a biodiversity hotspot: why do tall Eucalyptus forests in Southwest Australia exhibit low diversity?

Plant and Soil - Southwest Australia is a biodiversity hotspot, with greatest plant species diversity on the most severely phosphorus (P)-impoverished soils. Here, non-mycorrhizal species with...     

Evolution of competence and DNA uptake specificity in the Pasteurellaceae

Background  

Many bacteria can take up DNA, but the evolutionary history and function of natural competence and transformation remain obscure. The sporadic distribution of competence suggests it is frequently lost and/or gained, but this has not been examined in an explicitly phylogenetic context. Additional insight may come from the sequence specificity of uptake by species such as Haemophilus influenzae, where a 9 bp uptake signal sequence (USS) repeat is both highly overrepresented in the genome and needed for efficient DNA uptake. We used the distribution of competence genes and DNA uptake specificity in H. influenzae 's family, the Pasteurellaceae, to examine the ancestry of competence.     

Maintenance of growth rate at low temperature in rice and wheat cultivars with a high degree of respiratory homeostasis is associated with a high efficiency of respiratory ATP production

Some plants have the ability to maintain similar respiratory rates (measured at the growth temperature) when grown at different temperatures. This phenomenon is referred to as respiratory homeostasis. Using wheat and rice cultivars with different degrees of respiratory homeostasis (H), we previously demonstrated that high-H cultivars maintained shoot and root growth at low temperature [Kurimoto et al. (2004) Plant Cell Environ., 27: 853]. Here, we assess the relationship between respiratory homeostasis and the efficiency of respiratory ATP production, by measuring the levels of alternative oxidase (AOX) and uncoupling protein (UCP), which have the potential to decrease respiratory ATP production per unit of oxygen consumed. We also measured SHAM- and CN-resistant respiration of intact roots, and the capacity of the cytochrome pathway (CP) and AOX in isolated mitochondria. Irrespective of H, SHAM-resistant respiration of intact roots and CP capacity of isolated root mitochondria were larger when plants were grown at low temperature, and the maximal activity and relative amounts of cytochrome c oxidase showed a similar trend. In contrast, CN-resistant respiration of intact roots and relative amounts of AOX protein in mitochondria isolated from those roots, were lower in high-H plants grown at low temperature. In the roots of low-H cultivars, relative amounts of AOX protein were higher at low growth temperature. Relative amounts of UCP protein showed similar trends to AOX. We conclude that maintenance of growth rate in high-H plants grown at low temperature is associated with both respiratory homeostasis and a high efficiency of respiratory ATP production.     

Developmental physiology of cluster-root carboxylate synthesis and exudation in harsh hakea. Expression of phosphoenolpyruvate carboxylase and the alternative oxidase

Harsh hakea (Hakea prostrata R.Br.) is a member of the Proteaceae family, which is highly represented on the extremely nutrient-impoverished soils in southwest Australia. When phosphorus is limiting, harsh hakea develops proteoid or cluster roots that release carboxylates that mobilize sparingly soluble phosphate in the rhizosphere. To investigate the physiology underlying the synthesis and exudation of carboxylates from cluster roots in Proteaceae, we measured O2 consumption, CO2 release, internal carboxylate concentrations and carboxylate exudation, and the abundance of the enzymes phosphoenolpyruvate carboxylase and alternative oxidase (AOX) over a 3-week time course of cluster-root development. Peak rates of citrate and malate exudation were observed from 12- to 13-d-old cluster roots, preceded by a reduction in cluster-root total protein levels and a reduced rate of O2 consumption. In harsh hakea, phosphoenolpyruvate carboxylase expression was relatively constant in cluster roots, regardless of developmental stage. During cluster-root maturation, however, the expression of AOX protein increased prior to the time when citrate and malate exudation peaked. This increase in AOX protein levels is presumably needed to allow a greater flow of electrons through the mitochondrial electron transport chain in the absence of rapid ATP turnover. Citrate and isocitrate synthesis and accumulation contributed in a major way to the subsequent burst of citrate and malate exudation. Phosphorus accumulated by harsh hakea cluster roots was remobilized during senescence as part of their efficient P cycling strategy for growth on nutrient impoverished soils.     

The contribution of roots and shoots to whole plant nitrate reduction in fast- and slow-growing grass species

The hypothesis was tested that slow-growing grass species perform a greater proportion of total plant NO3- reduction in their roots than do fast-growing grasses. Eight grass species were selected that differed in maximum relative growth rate (RGR) and net NO3- uptake rate (NNUR). Plants were grown with free access to nutrients in hydroponics under controlled-environment conditions. The site of in vivo NO3- reduction was assessed by combining in vivo NO3- reductase activity (NRA) assays with biomass allocation data, and by analysing the NO3- to amino acid ratio of xylem sap. In vivo NRA of roots and shoots increased significantly with increasing NNUR and RGR. The proportion of total plant NO3- reduction that occurs in roots was found to be independent of RGR and NNUR, with the shoot being the predominant site of NO3- reduction in all species. The theoretical maximum proportion of whole plant nitrogen assimilation that could take place in the roots was calculated using information on root respiration rates, RGR, NNUR, and specific respiratory costs associated with growth, maintenance and ion uptake. The calculated maximum proportion that the roots can contribute to total plant NO3- reduction was 0.37 and 0.23 for the fast-growing Dactylis glomerata L. and the slow-growing Festuca ovina L., respectively. These results indicate that slow-growing grass species perform a similar proportion of total plant NO3- reduction in their roots to that exhibited by fast-growing grasses. Shoots appear to be the predominant site of whole plant NO3- reduction in both fast- and slow-growing grasses when plants are grown with free access to nutrients.