Growth under elevated atmospheric CO(2) concentration accelerates leaf senescence in sunflower (Helianthus annuus L.) plants

Some morphogenetic and metabolic processes were sensitive to a high atmospheric CO(2) concentration during sunflower primary leaf ontogeny. Young leaves of sunflower plants growing under elevated CO(2) concentration exhibited increased growth, as reflected by the high specific leaf mass referred to as dry weight in young leaves (16days). The content of photosynthetic pigments decreased with leaf development, especially in plants grown under elevated CO(2) concentrations, suggesting that high CO(2) accelerates chlorophyll degradation, and also possibly leaf senescence. Elevated CO(2) concentration increased the oxidative stress in sunflower plants by increasing H(2)O(2) levels and decreasing activity of antioxidant enzymes such as catalase and ascorbate peroxidase. The loss of plant defenses probably increases the concentration of reactive oxygen species in the chloroplast, decreasing the photosynthetic pigment content as a result. Elevated CO(2) concentration was found to boost photosynthetic CO(2) fixation, especially in young leaves. High CO(2) also increased the starch and soluble sugar contents (glucose and fructose) and the C/N ratio during sunflower primary leaf development. At the beginning of senescence, we observed a strong increase in the hexoses to sucrose ratio that was especially marked at high CO(2) concentration. These results indicate that elevated CO(2) concentration could promote leaf senescence in sunflower plants by affecting the soluble sugar levels, the C/N ratio and the oxidative status during leaf ontogeny. It is likely that systemic signals produced in plants grown with elevated CO(2), lead to early senescence and a higher oxidation state of the cells of these plant leaves.     

Impact of atmospheric CO2 on growth, photosynthesis and nitrogen metabolism in cucumber (Cucumis sativus L.) plants

Expression and activity of nitrate reductase (NR; EC 1.6.6.1) and glutamine synthetase (GS; EC 6.3.1.2) were analysed in relation to the rate of CO(2) assimilation in cucumber (Cucumis sativus L.) leaves. Intact plants were exposed to different atmospheric CO(2) concentrations (100, 400 and 1200microLL(-1)) for 14 days. A correlation between the in vivo rates of net CO(2) assimilation and the atmospheric CO(2) concentrations was observed. Transpiration rate and stomatal conductance remained unaffected by CO(2) levels. The exposure of the cucumber plants to rising CO(2) concentrations led to a concomitant increase in the contents of starch and soluble sugars, and a decrease in the nitrate content in leaves. At very low CO(2), NR and GS expression decreased, in spite of high nitrate contents, whereas at normal and elevated CO(2) expression and activity were high although the nitrate content was very low. Thus, in cucumber, NR and GS expression appear to be dominated by sugar levels, rather than by nitrate contents.     

Role of mammalian Rad54 in telomere length maintenance

The homologous recombination (HR) DNA repair pathway participates in telomere length maintenance in yeast but its putative role at mammalian telomeres is unknown. Mammalian Rad54 is part of the HR machinery, and Rad54-deficient mice show a reduced HR capability. Here, we show that Rad54-deficient mice also show significantly shorter telomeres than wild-type controls, indicating that Rad54 activity plays an essential role in telomere length maintenance in mammals. Rad54 deficiency also resulted in an increased frequency of end-to-end chromosome fusions involving telomeres compared to the controls, suggesting a putative role of Rad54 in telomere capping. Finally, the study of mice doubly deficient for Rad54 and DNA-PKcs showed that telomere fusions due to DNA-PKcs deficiency were not rescued in the absence of Rad54, suggesting that they are not mediated by Rad54 activity.     

Macrofilamentous microbial communities in the metal-rich and acidic River Tinto, Spain

A novel type of macroscopic microbial community consisting of large dendritic filaments (up to 1.5 m) in a pH 2.0 dam of the River Tinto (South-western Spain) is described. The combined use of 16S rRNA-gene surveys and fluorescent in situ hybridisation (FISH) suggested that gamma-proteobacteria and a relative large diversity of alpha-proteobacteria dominated these structures. beta-Proteobacteria, Actinobacteria and Firmicutes were also detected. Whereas acidophilic bacteria of the genera Acidithiobacillus, Leptospirillum and Acidiphilium, and archaea belonging to the Thermoplasmatales dominate mine acid drainage waters and streamers (riverbed filamentous biofilms), none of the lineages identified in this study affiliate to typical acid mine drainage acidophilic bacteria. Bacteria of the Tinto macrofilaments might be heterotrophic, and could be feeding on the organic matter entrapped in the filamentous structure.     

Phylogenetic Analysis of Eukaryotic Thiolases Suggests Multiple Proteobacterial Origins

Eukaryotic thiolases are essential enzymes located in three different compartments (peroxisome, mitochondrion, and cytosol) that can display catabolic or anabolic functions. They are responsible for the thiolytic cleavage of oxidized acyl-CoA (thiolase I; EC 2.3.1.16) and the synthesis or degradation of acetoacetyl-CoA (thiolase II; EC 2.3.1.9). Phylogenetic analysis of eukaryotic thiolase sequences showed that they form six distinct clusters, one of them highly divergent, which are in good correlation with their class and subcellular location. When analyzed together with a representative sample of prokaryotic thiolases, all eukaryotic thiolase groups emerged close to proteobacterial sequences. Metazoan cytosolic thiolase II was related to α-proteobacterial sequences, suggesting a mitochondrial origin. Unexpectedly, cytosolic thiolases from green plants and fungi as well as at least one member of all eukaryotic peroxisomal and mitochondrial thiolases had δ-proteobacteria as closest relatives. Our analysis suggests that these eukaryotic peroxisomal and mitochondrial thiolases may have been acquired from δ-proteobacteria prior to the ancestor of all known eukaryotes.     

Polyubiquitin insertions and the phylogeny of Cercozoa and Rhizaria

A single or double amino acid insertion at the monomer-monomer junction of the universal eukaryotic protein polyubiquitin is unique to Cercozoa and Foraminifera, closely related 'core' phyla in the protozoan infrakingdom Rhizaria. We screened 11 other candidate rhizarians for this insertion: Radiozoa (polycystine and acantharean radiolaria), a 'microheliozoan', and Apusozoa; all lack it, supporting suggestions that Foraminifera are more closely related to Cercozoa than either is to other eukaryotes. The insertion's size was ascertained for 12 additional Cercozoa to help resolve their basal branching order. The earliest branching Cercozoa generally have a single amino acid insertion, like all Foraminifera, but a large derived clade consisting of all Monadofilosa except Metopion, Helk-esimastix, and Cercobodo agilis has two amino acids, suggesting one doubling event and no reversions to a single amino acid. Metromonas and Sainouron, cercozoans of uncertain position, have a double insertion, suggesting that they belong in Monadofilosa. An alternative interpretation, suggested by the higher positions for Metopion and Cercobodo on Bayesian trees compared with most distance trees, cannot be ruled out, i.e. that the second insertion took place earlier, in the ancestral filosan, and was followed by three independent reversions to a single amino acid in Chlorarachnea, Metopion and Cercobodo.     

Methyl jasmonate increases silymarin production in Silybum marianum (L.) Gaernt cell cultures treated with β-cyclodextrins

Silymarin (Sm) from the fruit of Silybum marianum is an isomeric mixture of pharmacologically active flavonolignans which are formed by oxidative coupling of taxifolin (Tx) and coniferyl alcohol (CA). Suspension cultures of this plant constitutively secrete small amounts of Sm into the extracellular medium. Production can be increased by inclusion of cyclodextrins (CDs) in cultures. Both hydroxylated (RHCD) and dimethylated (RMCD) CDs strongly induced prompt accumulation of CA in the medium followed by a late production of flavonolignans. Simultaneous addition of methyl jasmonate (MJ) and RMCD to cells did not significantly modify CA release or flavonolignan accumulation. Delayed addition of MJ to cultures subcultivated in medium containing RMCD markedly influenced Sm production by promoting conversion of the previously formed CA precursor.