HSP90 and checkpoint-dependent lengthening of the G2 phase observed in plant cells under hypoxia and cold

Proliferating cells of Allium cepa L. roots became adapted to hypoxia (5% oxygen) and cold (10°C) by acquiring new steady-state kinetics of growth. The cell cycle time increased from the 17.6 h in control meristems up to 29.7 and 69.0 h under hypoxia and cold conditions, respectively. Acclimation of the proliferating cells was stress specific. No acclimation took place after 24 h of heat treatment (40°C). Under cold treatment, all cycle phases enlarged uniformly. However, under hypoxia, while the G1 and S cycle phases roughly doubled in their timing, the expected checkpoint-dependent lengthening of G2 did not take place. This failure in lengthening G2 in response to hypoxia correlated with a failure in the overinduction of a single peptide with a molecular mass of about 134 kDa which is among those recognised by an HSP90 antibody. Moreover, the presence of this large peptide of the HSP90 family proved to be a marker for cell proliferation. It was always absent from the contiguous differentiated cells of the root. Lastly, the mitochondrial chaperonin recognized by an HSP60 antibody in these roots not involved in photosynthesis was always higher in the proliferating than in the nonproliferating cells

A large-scale screen in S. pombe identifies seven novel genes required for critical meiotic events

Meiosis is a specialized form of cell division by which sexually reproducing diploid organisms generate haploid gametes. During a long prophase, telomeres cluster into the bouquet configuration to aid chromosome pairing, and DNA replication is followed by high levels of recombination between homologous chromosomes (homologs). This recombination is important for the reductional segregation of homologs at the first meiotic division; without further replication, a second meiotic division yields haploid nuclei. In the fission yeast Schizosaccharomyces pombe, we have deleted 175 meiotically upregulated genes and found seven genes not previously reported to be critical for meiotic events. Three mutants (rec24, rec25, and rec27) had strongly reduced meiosis-specific DNA double-strand breakage and recombination. One mutant (tht2) was deficient in karyogamy, and two (bqt1 and bqt2) were deficient in telomere clustering, explaining their defects in recombination and segregation. The moa1 mutant was delayed in premeiotic S phase progression and nuclear divisions. Further analysis of these mutants will help elucidate the complex machinery governing the special behavior of meiotic chromosomes. ©2005 Elsevier Ltd All rights reserved.Peer Reviewe

Complex Formation via Hydrogen bonding between Rhodamine B and Montmorillonite in Aqueous Solution

Abstract This study investigates the adsorption mechanism differences among four nitrogenous dyes, sulforhodamine G (SRG), uncharged/deprotonated rhodamine B (RhB), orange II (Or II) and methyl blue (MB) by montmorillonite (MMT). MMT adsorption capacity for cationic MB was three times that of uncharged RhB and anionic SRG, while anionic Or II was not absorbed. Colloidal MMT particles have two types of surfaces, basal and edge, that interact with nitrogenous dyes very differently. The surface acidity of MMT was characterized with the pyridine adsorption method using in-situ diffuse reflectance infrared Fourier transform spectroscopy (in-situ DRIFTS). Adsorption of cationic MB was compared with the adsorption of RhB. In-situ attenuated total reflectance Fourier transform infrared (in-situ ATR-FTIR) spectroscopy indicated that a nitrogen atom on RhB complexes with a metal hydroxyl on an MMT edge through a water bridge. The highly polar edge hydroxyl is important to hydrogen bond formation. Cation ion exchange and washing experiments, as well as studies on the effect of temperature, pH and ionic strength on adsorption further clarified the adsorption mechanism. Our results provide insights into the effects of molecular structure on the adsorption of nitrogenous dyes by clay and the role of edge surfaces in the adsorption process