Brassinosteroids control meristem size by promoting cell cycle progression in Arabidopsis roots

Brassinosteroids (BRs) play crucial roles in plant growth and development. Previous studies have shown that BRs promote cell elongation in vegetative organs in several plant species, but their contribution to meristem homeostasis remains unexplored. Our analyses report that both loss- and gain-of-function BR-related mutants in Arabidopsis thaliana have reduced meristem size, indicating that balanced BR signalling is needed for the optimal root growth. In the BR-insensitive bri1-116 mutant, the expression pattern of the cell division markers CYCB1;1, ICK2/KRP2 and KNOLLE revealed that a decreased mitotic activity accounts for the reduced meristem size; accordingly, this defect could be overcome by the overexpression of CYCD3;1. The activity of the quiescent centre (QC) was low in the short roots of bri1-116, as reported by cell type-specific markers and differentiation phenotypes of distal stem cells. Conversely, plants treated with the most active BR, brassinolide, or mutants with enhanced BR signalling, such as bes1-D, show a premature cell cycle exit that results in early differentiation of meristematic cells, which also negatively influence meristem size and overall root growth. In the stem cell niche, BRs promote the QC renewal and differentiation of distal stem cells. Together, our results provide evidence that BRs play a regulatory role in the control of cell-cycle progression and differentiation in the Arabidopsis root meristem.     

Influence of squalene on lipid particle/droplet and membrane organization in the yeast Saccharomyces cerevisiae

In a previous study (Spanova et al., 2010, J. Biol. Chem., 285, 6127-6133) we demonstrated that squalene, an intermediate of sterol biosynthesis, accumulates in yeast strains bearing a deletion of the HEM1 gene. In such strains, the vast majority of squalene is stored in lipid particles/droplets together with triacylglycerols and steryl esters. In mutants lacking the ability to form lipid particles, however, substantial amounts of squalene accumulate in organelle membranes. In the present study, we investigated the effect of squalene on biophysical properties of lipid particles and biological membranes and compared these results to artificial membranes. Our experiments showed that squalene together with triacylglycerols forms the fluid core of lipid particles surrounded by only a few steryl ester shells which transform into a fluid phase below growth temperature. In the hem1? deletion mutant a slight disordering effect on steryl esters was observed indicated by loss of the high temperature transition. Also in biological membranes from the hem1? mutant strain the effect of squalene per se is difficult to pinpoint because multiple effects such as levels of sterols and unsaturated fatty acids contribute to physical membrane properties. Fluorescence spectroscopic studies using endoplasmic reticulum, plasma membrane and artificial membranes revealed that it is not the absolute squalene level in membranes but rather the squalene to sterol ratio which mainly affects membrane fluidity/rigidity. In a fluid membrane environment squalene induces rigidity of the membrane, whereas in rigid membranes there is almost no additive effect of squalene. In summary, our results demonstrate that squalene (i) can be well accommodated in yeast lipid particles and organelle membranes without causing deleterious effects; and (ii) although not being a typical membrane lipid may be regarded as a mild modulator of biophysical membrane properties.     

Development of a pattern in biochemical parameters in the core and penumbra during infarct evolution after transient MCAO in rats

The period from stroke initiation to the cessation of penumbra damage spread represents a therapeutic window when expansion can be alleviated. In the present work, we studied some biochemical parameters helpful for the estimation of infarct progression and thus for the application of interventions.     

Silicon modifies root anatomy, and uptake and subcellular distribution of cadmium in young maize plants

Background and Aims

Silicon (Si) has been shown to ameliorate the negative influence of cadmium (Cd) on plant growth and development. However, the mechanism of this phenomenon is not fully understood. Here we describe the effect of Si on growth, and uptake and subcellular distribution of Cd in maize plants in relation to the development of root tissues.

Methods

Young maize plants (Zea mays) were cultivated for 10 d hydroponically with 5 or 50 µm Cd and/or 5 mm Si. Growth parameters and the concentrations of Cd and Si were determined in root and shoot by atomic absorption spectrometry or inductively coupled plasma mass spectroscopy. The development of apoplasmic barriers (Casparian bands and suberin lamellae) and vascular tissues in roots were analysed, and the influence of Si on apoplasmic and symplasmic distribution of ¹⁰⁹Cd applied at 34 nm was investigated between root and shoot.

Key Results

Si stimulated the growth of young maize plants exposed to Cd and influenced the development of Casparian bands and suberin lamellae as well as vascular tissues in root. Si did not affect the distribution of apoplasmic and symplasmic Cd in maize roots, but considerably decreased symplasmic and increased apoplasmic concentration of Cd in maize shoots.

Conclusions

Differences in Cd uptake of roots and shoots are probably related to the development of apoplasmic barriers and maturation of vascular tissues in roots. Alleviation of Cd toxicity by Si might be attributed to enhanced binding of Cd to the apoplasmic fraction in maize shoots.     

Bradykinin Postconditioning Protects Pyramidal CA1 Neurons Against Delayed Neuronal Death in Rat Hippocampus

Aims The present study was undertaken to evaluate possible neuroprotective effect of bradykinin against delayed neuronal death in hippocampal CA1 neurons if applied two days after transient forebrain ischemia in the rat. Methods Transient forebrain ischemia was induced in male Wistar rats by four-vessel occlusion for 8 min. To assess efficacy of bradykinin as a new stressor for delayed postconditioning we used two experimental groups of animals: ischemia 8 min and 3 days of survival, and ischemia 8 min and 3 days of survival with i.p. injection of bradykinin (150 μg/kg) applied 48 h after ischemia. Results We found extensive neuronal degeneration in the CA1 region at day 3 after ischemia/reperfusion. The postischemic neurodegeneration was preceded by increased activity of mitochondrial enzyme MnSOD in cytoplasm, indicating release of MnSOD from mitochondria in the process of delayed neuronal death. Increased cytosolic cytochrome c and subsequently caspase-3 activation are additional signs of neuronal death via the mitochondrial pathway. Bradykinin administration significantly attenuated ischemia-induced neuronal death, and also suppressed the release of MnSOD, and cytochrome c, and prevented caspase-3 activation. Conclusions Bradykinin can be used as an effective stressor able to prevent mitochondrial failure leading to apoptosis-like delayed neuronal death in postischemic rat hippocampus.     

Mitochondrial haplogroup N1a phylogeography,with implication to the origin of European farmers

Background  

Tracing the genetic origin of central European farmer N1a lineages can provide a unique opportunity to assess the patterns of the farming technology spread into central Europe in the human prehistory. Here, we have chosen twelve N1a samples from modern populations which are most similar with the farmer N1a types and performed the complete mitochondrial DNA genome sequencing analysis. To assess the genetic and phylogeographic relationship, we performed a detailed survey of modern published N1a types from Eurasian and African populations.     

Complementation of the Chlamydomonas reinhardtii arg7-8 (arg2) point mutation by recombination with a truncated nonfunctional ARG7 gene

Chlamydomonas reinhardtii arg7-8 (arg2) mutant strains carrying a hitherto undescribed mutation in their argininosuccinate lyase gene (ARG7) that leads to arginine auxotrophy have been used together with the corresponding wild-type gene as a very reliable transformation system since 1989. In this study, we finally identify the molecular nature of the arg7-8 mutation as a (6073)G to A transition in exon 9 of ARG7 leading to a (288)Gly to Ser exchange near the active site of the protein. The same mutation was found in the ARG7 genes of three commonly used C. reinhardtii laboratory strains, namely cw15-302 arg2, CC-48, and CC-1618. We did not observe exact spontaneous reversion of the arg7-8 allele in our study, but did identify two different and rare intragenic suppressor mutations, (27)Leu to Phe and (285)Tyr to Phe. In our hands, only transformation of the arg7-8 strain with a truncated nonfunctional wild-type ARG7 gene lacking 124 codons at its 5' end led to exact reversion of the mutant base (6073)A to the wild-type (6073)G, presumably by recombination. This system offers a positive selection scheme for homologous recombination (HR) and may, therefore, be useful to the methodical improvement of recombination in Chlamydomonas.     

Secondary alcohol dehydrogenase catalyzes the reduction of exogenous acetone to 2-propanol in Trichomonas vaginalis

Secondary alcohols such as 2-propanol are readily produced by various anaerobic bacteria that possess secondary alcohol dehydrogenase (S-ADH), although production of 2-propanol is rare in eukaryotes. Specific bacterial-type S-ADH has been identified in a few unicellular eukaryotes, but its function is not known and the production of secondary alcohols has not been studied. We purified and characterized S-ADH from the human pathogen Trichomonas?vaginalis. The kinetic properties and thermostability of T.?vaginalis S-ADH were comparable with bacterial orthologues. The substantial activity of S-ADH in the parasite's cytosol was surprising, because only low amounts of ethanol and trace amounts of secondary alcohols were detected as metabolic end products. However, S-ADH provided the parasite with a high capacity to scavenge and reduce external acetone to 2-propanol. To maintain redox balance, the demand for reducing power to metabolize external acetone was compensated for by decreased cytosolic reduction of pyruvate to lactate and by hydrogenosomal metabolism of pyruvate. We speculate that hydrogen might be utilized to maintain cytosolic reducing power. The high activity of Tv-S-ADH together with the ability of T.?vaginalis to modulate the metabolic fluxes indicate efficacious metabolic responsiveness that could be advantageous for rapid adaptation of the parasite to changes in the host environment.     

Silicon improves salinity tolerance and affects ammonia assimilation in maize roots

The present study was conducted to evaluate the effect of different salt concentrations (50 and 200 mM NaCl) on growth, permeability properties (electrolyte leakage, cell viability) and activity of glutamine synthetase (GS) and glutamate dehydrogenase (GDH) in roots of maize seedlings. Both salt concentrations significantly affected growth and permeability properties of maize seedling roots and this negative effect increased with concentration of salt and duration of experiments. On the other hand salinity induced only small changes in the activities of GS and GDH, usually small increase in the activity was observed. To characterise the possible protective effect of silicon (Si) on maize roots exposed to saline stress, different concentrations of Si were simultaneously applied to both, low (50 mM) and high (200 mM) salt concentrations. Possible protective effects of Si on studied parameters were analysed in time range of 3 days treatment with the most positive effect on salt-induced root growth inhibition at high salt concentration and electrolyte leakage. The results show significant increase in GDH activity under all the tested conditions, although the mechanisms underlying this increase have not been elucidated. The results indicate that silicon may ameliorate the salt-induced root growth inhibition and increase the plant vigour at stressful conditions.     

Disuniting uniformity: a pied cladistic canvas of mtDNA haplogroup H in Eurasia

It has been often stated that the overall pattern of human maternal lineages in Europe is largely uniform. Yet this uniformity may also result from an insufficient depth and width of the phylogenetic analysis, in particular of the predominant western Eurasian haplogroup (Hg) H that comprises nearly a half of the European mitochondrial DNA (mtDNA) pool. Making use of the coding sequence information from 267 mtDNA Hg H sequences, we have analyzed 830 mtDNA genomes, from 11 European, Near and Middle Eastern, Central Asian, and Altaian populations. In addition to the seven previously specified subhaplogroups, we define fifteen novel subclades of Hg H present in the extant human populations of western Eurasia. The refinement of the phylogenetic resolution has allowed us to resolve a large number of homoplasies in phylogenetic trees of Hg H based on the first hypervariable segment (HVS-I) of mtDNA. As many as 50 out of 125 polymorphic positions in HVS-I were found to be mutated in more than one subcluster of Hg H. The phylogeographic analysis revealed that sub-Hgs H1*, H1b, H1f, H2a, H3, H6a, H6b, and H8 demonstrate distinct phylogeographic patterns. The monophyletic subhaplogroups of Hg H provide means for further progress in the understanding of the (pre)historic movements of women in Eurasia and for the understanding of the present-day genetic diversity of western Eurasians in general.