Activity of a protein inhibitor of polygalacturonase in potato plants

The activity of a protein inhibitor of polygalacturonase (PIPG) was studied in potato tubers during storage and in potato leaves and stems during vegetation. The activity of PIPG in tubers varied between seasons. The activity of PIPG during dormancy changed depending on the storage stage and temperature. As a rule, it was higher in etiolated sprouts than in the tubers. The activity of PIPG was slightly higher in leaves of adult vegetating plants than in stems and decreased by the end of vegetation. These changes in the activity of PIPG are suggested to be associated with changes in the growth rate.     

Reduction in Turgor Pressure as a Result of Extremely Brief Exposure to CO(2)

CO₂ depresses water influx into sunflower hypocotyl segments of low water potential; by contrast, it stimulates flux into segments of high water potential. When segments of high potential were placed in a series of mannitol concentrations and allowed to achieve steady rates of water uptake, influx into CO₂-treated tissue in a solution of 3 atm equalled that into control tissue in water. Reasons are given for deducing that a change in internal osmotic concentration (π_i) of the order of 40% would be necessary to account for this result on the basis of π_i. Direct measurements (by cryoscopy and by the minimum volume method) detected no difference in the steady state value for π_i as between CO₂-treated and control tissue. It was therefore concluded that CO₂ had caused some reduction in turgor pressure.

Water uptake into tissue treated with CO₂ for only the first 2 minutes of a 30-minute period was equal to that into tissue treated continuously with CO₂, i.e. 3 times the control value. Ten seconds' CO₂ treatment produced a significant stimulation. When the cycles of treatment were repeated the samples receiving flashes of CO₂ maintained a rate of water uptake superior to that of the control, whereas influx into continuously treated tissue fell below the control value after 1 hour.

CO₂ treatment applied in a moist air chamber stimulated subsequent water influx when the tissue was transferred to water. Fifteen seconds' treatment was sufficient to produce a marked effect. Even when a transition period of 30 minutes in the moist chamber was interposed between CO₂ treatment (5 minutes) and transfer to water, a stimulation was observed. The CO₂ effect could be achieved at zero degrees; 5 minutes' treatment in the moist chamber at zero degrees, followed by a 15-minute transition period at the same temperature, substantially increased subsequent water uptake at 25°.

     

Loss of CDK5RAP2 affects neural but not non-neural mESC differentiation into cardiomyocytes

Biallelic mutations in the gene encoding centrosomal CDK5RAP2 lead to autosomal recessive primary microcephaly (MCPH), a disorder characterized by pronounced reduction in volume of otherwise architectonical normal brains and intellectual deficit. The current model for the microcephaly phenotype in MCPH invokes a premature shift from symmetric to asymmetric neural progenitor-cell divisions with a subsequent depletion of the progenitor pool. The isolated neural phenotype, despite the ubiquitous expression of CDK5RAP2, and reports of progressive microcephaly in individual MCPH cases prompted us to investigate neural and non-neural differentiation of Cdk5rap2-depleted and control murine embryonic stem cells (mESC). We demonstrate an accumulating proliferation defect of neurally differentiating Cdk5rap2-depleted mESC and cell death of proliferative and early postmitotic cells. A similar effect does not occur in non-neural differentiation into beating cardiomyocytes, which is in line with the lack of non-central nervous system features in MCPH patients. Our data suggest that MCPH is not only caused by premature differentiation of progenitors, but also by reduced propagation and survival of neural progenitors.     

The Effect of Plant Polygalaturonase-Inhibiting Protein on the Rate of Oligouronide Formation

The effects of the polygalacturonase-inhibiting protein (PGIP) on the rate of oligouronide formation were studied in a model system containing polygalacturonic acid and polygalacturonase (PG) from the culture medium of phytopathogenic fungi. PGIP preparations were prepared from stored potato tubers and sprouts and also from apple fruits. The PGIP effects on oligouronide synthesis depended markedly on the physiological state of the source plant. Apple cultivars differing in their earliness differed in PGIP effects as well. The PGIP from potato tubers, which were in deep dormancy, suppressed oligouronide formation. The inhibitory PGIP action was decreased after dormancy release and tuber sprouting, which resulted in the oligouronide accumulation. The effects of PGIP from apple fruits on the oligouronide synthesis in the system containing PG from various phytopathogenic fungi were not correlated with tissue damage induced by these fungi. The PGIP effects on oligouronide formation are evident; however, their role in plant-cell processes related to the pectin compound conversions and plant resistance to diseases remains to be elucidated.     

New anti-MRSA cephalosporins with a basic aminopyridine at the C-7 position

Incorporation of a basic aminopyridine into the C-7 position of 3-(amine-substituted arylthio)-3-norcephalosporins, as in 3, afforded high potency against MRSA and acceptable solubility for intravenous administration.     

Demography and natural selection have shaped genetic variation in Drosophila melanogaster: a multi-locus approach

Demography and selection have been recognized for their important roles in shaping patterns of nucleotide variability. To investigate the relative effects of these forces in the genome of Drosophila melanogaster, we used a multi-locus scan (105 fragments) of X-linked DNA sequence variation in a putatively ancestral African and a derived European population. Surprisingly, we found evidence for a recent size expansion in the African population, i.e., a significant excess of singletons at a chromosome-wide level. In the European population, such an excess was not detected. In contrast to the African population, we found evidence for positive natural selection in the European sample: (i) a large number of loci with low levels of variation and (ii) a significant excess of derived variants at the low-variation loci that are fixed in the European sample but rare in the African population. These results are consistent with the hypothesis that the European population has experienced frequent selective sweeps in the recent past during its adaptation to new habitats. Our study shows the advantages of a genomic approach (over a locus-specific analysis) in disentangling demographic and selective forces.     

R-Spondin2 is a secreted activator of Wnt/beta-catenin signaling and is required for Xenopus myogenesis

We have carried out a small pool expression screen for modulators of the Wnt/beta-catenin pathway and identified Xenopus R-spondin2 (Rspo2) as a secreted activator of this cascade. Rspo2 is coexpressed with and positively regulated by Wnt signals and synergizes with Wnts to activate beta-catenin. Analyses of functional interaction with components of the Wnt/beta-catenin pathway suggest that Rspo2 functions extracellularly at the level of receptor ligand interaction. In addition to activating the Wnt/beta-catenin pathway, Rspo2 overexpression blocks Activin, Nodal, and BMP4 signaling in Xenopus, raising the possibility that it may negatively regulate the TGF-beta pathway. Antisense Morpholino experiments in Xenopus embryos and RNAi experiments in HeLa cells reveal that Rspo2 is required for Wnt/beta-catenin signaling. In Xenopus embryos depleted of Rspo2, the muscle markers myoD and myf5 fail to be activated and later muscle development is impaired. Thus, Rspo2 functions in a positive feedback loop to stimulate the Wnt/beta-catenin cascade.     

Combinatorial signalling by Xwnt-11 and Xnr3 in the organizer ephithelium

The epithelium of the Spemann organizer plays an important role in embryonic axis formation and transplantation experiments have shown that epithelial organizer cells have potent axis-inducing potential. Known axis-inducing molecules like noggin and chordin are not expressed in the epithelium and cannot account for its inductive properties. Xwnt-11 is expressed in the epithelium but has only poor dorsalizing activity. In an expression screen for genes that are able to functionally cooperate with Xwnt-11 we have identified a cDNA encoding Xenopus nodal-related 3 (Xnr3), a member of the TGF-β family, coexpressed with Xwnt-11 in the organizer epithelium. Xwnt-11 and Xnr3 act highly cooperatively in inducing secondary embryonic axes and dorsalizing ventral mesoderm. Xwnt-11/Xnr3 interfere with BMP signalling without themselves inducing chordin or noggin. The results indicate that induction by the organizer epithelium may result from the combinatorial action of instructive Xnr3 and permissive Xwnt-11 signalling.     

Differential regulation of protein biosynthesis at translational level in the fat body cells of adult Locusta migratoria

Vitellogenin (Vg) and lipophorin (Lp) are synthesized by the fat body of adult locust (Locusta migratoria) females. We have shown by an immunohistochemical technique that both proteins are produced in the same cells of the fat body. The rate of Vg synthesis was measured with the use of double immunoprecipitation of labeled proteins at oviposition and 24 h later. It was found that the rate of Vg synthesis declined significantly by the time of oviposition; however, 24 h later, it was raised to the highest possible level. The rate of Lp synthesis remained constant at both indicated points. The similar postlaying increase in the Vg synthesis rate was observed in the fat bodies of females treated by alpha-amanitin immediately after oviposition. The data provide evidence that Vg biosynthesis in L. migratoria is regulated by selective periodical repression and derepression of Vg mRNAs in the fat body cells but not by total inhibition and stimulation of protein-synthesizing machinery.     

Abscisic Acid promotes both volume flow and ion release to the xylem in sunflower roots

The effect of abscisic acid (ABA) on the exudation process in excised sunflower root was investigated. A promotion of both ion flux and volume exudation rate was observed. Cutting off the external supply of ions to the roots markedly increased the magnitude of the ABA effect. The promotive effect of ABA on exudation rate was extremely rapid (less than 6 minutes) and seemed to be biphasic. Reasons are given for relating the ABA effect to two separate actions, namely: (a) on water permeability; and (b) on the release of ions both from vacuoles to the cytoplasm and from symplasm to the xylem. Kinetin inhibited movement of ions to the xylem and its effect did not appear to be related to that of the ABA.