Ribulose-1,5-bisphosphate Carboxylase/Oxygenase and Polyphenol Oxidase in the Tobacco Mutant Su/su and Three Green Revertant Plants

Ribulose-1,5-bisphosphate carboxylase/oxygenase (EC 4.1.1.39) was crystallized from a heterozygous tobacco (Nicotiana tabacum L.) aurea mutant (Su/su), its wild-type sibling (su/su), and green revertant plants regenerated from green spots found on leaves of haploid Su plants. No differences were found in the specific activity or kinetic parameters of this enzyme, when comparing Su/su and su/su plants of the same age, which had been grown under identical conditions. The enzyme crystallized from revertant plants was also identical to the enzyme from wild-type plants with the exception of one clone, designated R2. R2 has a chromosome number approximately double that of the wild-type (87.0 ± 11.1 versus 48). The enzyme from R2 had a lower V_max for CO₂, although the K_m values were identical to those for the enzyme from the wild-type plant. The enzyme from all mutant plants had identical isoelectric points, identical molecular weight as demonstrated by migration on native and sodium dodecyl sulfate (SDS)-polyacrylamide gels, and the same ratio of large to small subunits as the enzyme from the wild-type. The large subunit of the enzyme from tobacco leaves exhibited a different electrophoretic pattern than did the large subunit from spinach; there were two to three bands on SDS-polyacrylamide gels for the tobacco enzyme whereas the enzyme from spinach had only one species of large subunit.     

Hepatocyte Growth Factor Activator Inhibitor-1 Is Induced by Bone Morphogenetic Proteins and Regulates Proliferation and Cell Fate of Neural Progenitor Cells

Background

Neural progenitor cells (NPCs) in the developing neuroepithelium are regulated by intrinsic and extrinsic factors. There is evidence that NPCs form a self-supporting niche for cell maintenance and proliferation. However, molecular interactions and cell-cell contacts and the microenvironment within the neuroepithelium are largely unknown. We hypothesized that cellular proteases especially those associated with the cell surface of NPCs play a role in regulation of progenitor cells in the brain.

Methodology/Principal Findings

In this work, we show that NPCs, isolated from striatal anlage of developing rat brain, express hepatocyte growth factor activator inhibitor-1 and -2 (HAI-1 and HAI-2) that are cell surface-linked serine protease inhibitors. In addition, radial glia cells derived from mouse embryonic stem cells also express HAI-1 and HAI-2. To study the functional significance of HAI-1 and HAI-2 in progenitor cells, we modulated their levels using expression plasmids or silencing RNA (siRNA) transfected into the NPCs. Data showed that overexpression of HAI-1 or HAI-2 decreased cell proliferation of cultured NPCs, whilst their siRNAs had opposite effects. HAI-1 also influenced NPC differentiation by increasing the number of glial fibrillary acidic protein (GFAP) expressing cells in the culture. Expression of HAI-1 in vivo decreased cell proliferation in developing neuroepithelium in E15 old animals and promoted astrocyte cell differentiation in neonatal animals. Studying the regulation of HAI-1, we observed that Bone morphogenetic protein-2 (BMP-2) and BMP-4 increased HAI-1 levels in the NPCs. Experiments using HAI-1-siRNA showed that these BMPs act on the NPCs partly in a HAI-1-dependent manner.

Conclusions

This study shows that the cell-surface serine protease inhibitors, HAI-1 and HAI-2 influence proliferation and cell fate of NPCs and their expression levels are linked to BMP signaling. Modulation of the levels and actions of HAI-1 in NPCs may be of a potential value in stem cell therapies in various brain diseases.     

Biochemische Untersuchungen über Bakteriensporen

Ohne Zusammenfassung     

The Effect of Prevention of Flowering on the Vegetative Growth of Inoculated Pea Plants

The removal of the apical buds from the top of inoculated pea ptants before flowering caused the axillary buds of the stem leaves to develop and thus further to branch. The vegetative growth of the test plants continued to be luxuriant when blooming was delayed. While the control ptants formed seeds and ripined. the vegetative growth of the stem of the test ptants increased at most eight-fold during the same time. A new, additional red part grew at the same time in the root nodules, which had already partly become green. The new red part branched later so that the imusuatty large nodules appeared quite odd. The weight of the branched, large nodules had at the same time increased on the average six-fold and the vegetatively grown test plants synthesized even eight times more nitrogen than did the control plants. The concentration of teghaemoglobin in the nodules formed by the bacterial strain used in the experiment was not inereased, but the absolute amount of the pigment was raised six-fold as a result of the increased nodule mass. While the vegetative growth was going on, oxidation of the leghaemoglobin was delayed. Analyses of nitrogen and amino acids were made for both test and control plants. The total length of the branches in the largest test plant was 32 m compared with the unbranched control plant which was 1.30 m.     

Competition ofRhizobium strains in nodule-formation

Summary By the use of a sterile culture system experiments have been carried out with peas in order to elucidate to what extent inoculation with an ineffective bacterial strain effects the ability of an effective strain to produce further nodulation. It has been established that effective strains, when applied to the plant after the formation of the first nodules by an ineffective strain, altogether fail to form nodules or the nodulation is delayed very much. Differences are noted in this respect between different bacterial strains. The results can be explained easiest by assuming that the strain first entering the roots causes an immunity in the plant against later infections. Other possibilities for explanation are also discussed. The conception that the resistance would be due to the saturation of roots with nodules formed by the first strain which would inhibit further nodulation is not in accordance with the results recorded.A method has been introduced for cultivation of plants under sterile conditions by dividing the roots into two or more culture flasks. This method is of great value when the nutrient uptake of plants is elucidated. Successive inoculation with ineffective and effective strains gave varying results by this technique. The experiments seem to imply that if only a part of the root system is inoculated with an ineffective strain, immunity does not regularly occur against later infections by effective strains. This suggests that the immunity is a somewhat local phenomenon.