The relative contributions of sexual reproduction and clonal propagation in Opuntia rastrera from two habitats in the Chihuahuan Desert

1 The clonal cactus Opuntia rastrera shows predominantly sexual reproduction in grasslands (GH) and clonal propagation in nopaleras (NH). We assessed the effects of light, herbivory, water availability and the habitat an offspring came from on the survival and growth of sexual or clonal offspring (i.e. seedlings and cladodes), through 3- and 4-year common garden and short-term greenhouse experiments.
2 Shading by nurse plants increased seedling survival in the field by an order of magnitude, and a small additional advantage due to predator protection by grasses was observed. Strong herbivory transforms a facultative nurse–protégé relationship for seedlings into an obligatory one.
3 In the greenhouse seedlings grew better under shade, but in the field the production of the first cladode was delayed in seedlings in the more shaded GH. Competition for soil resources may be more intense under a dense grass tussock than under a open shrub, thus affecting the nurse–protégé relationship. Seedling survival under nurse plants was similar in GH and NH, but higher plant cover suggests that a larger number of seedlings will establish in GH in the long term.
4 Cladode survival was higher in NH. Cladodes were more successful than seedlings at establishing in intercanopy areas, possibly due to physiological differences as well as their ability to survive partial predation. Cladode survival in intercanopy areas may explain the enhanced clonal propagation in the more open NH scrubland, together with their susceptibility to the flooding which affects GH.
5 The high seedling and cladode survival in the greenhouse experiments contrasted with that observed in the field, indicating that survival is determined by the interaction between herbivores, plants and abiotic conditions rather than the physiological aptitude of the plants.     

Isocitrate dehydrogenases and oxoglutarate dehydrogenase activities of baker's yeast grown in a variety of hypoxic conditions

Molecular and Cellular Biochemistry - The activities of isocitrate dehydrogenase (NAD), isocitrate dehydrogenase (NADP) and oxoglutarate dehydrogenase have been investigated inSaccharomyces...     

The active center of catalase

The refined structure of beef liver catalase (I. Fita, A. M. Silva, M. R. N. Murthy & M. G. Rossmann, unpublished results) is here examined with regard to possible catalytic mechanisms. The distal side of the deeply buried heme pocket is connected with the surface of the molecule by one (or possibly two) channel. The electron density representing the heme group, in each of the two crystallographically independent subunits, is consistent with degradation of the porphyrin rings. The heme group appears to be buckled, reflecting the high content of bile pigment in liver catalase. The spatial organization on the proximal side (where the fifth ligand of the iron is located) shows an elaborate network of interactions. The distal side contains the substrate pocket. The limited space in this region severely constrains possible substrate positions and orientations. The N delta atom of the essential His74 residue hydrogen bonds with O gamma of Ser113, which in turn hydrogen bonds to a water molecule associated with the propionic carbonylic group of pyrrole III. These interactions are also visible in the refined structure of Penicillium vitale catalase (B. K. Vainshtein, W. R. Melik-Adamyan, V. V. Barynin, A. A. Vagin, A. I. Grebenko, V. V. Borisov, K. S. Bartels, I. Fita, & M. G. Rossmann, unpublished results). Model building suggests a pathway for a catalase mechanism (compound I formation, as well as catalatic and peroxidatic reactions). There are some similarities in compound I formation of catalase and cytochrome c peroxidase.     

Growth and cell wall changes in rice coleoptiles growing under different conditions I. Changes in turgor pressure and cell wall polysaccharides during intact growth

The effect of the oxygen supply on growth, water absorptionof cells and cell wall changes was studied in coleoptiles ofrice seedlings growing under three different conditions: underwater, under water with constant air bubbling and in air. Coleoptilegrowth was larger when they were grown under water than in waterwith air bubbling and in air. Coleoptile growth under waterwas limited by the suction force of their cells rather thanby mechanical properties of the cell wall, while that of thecoleoptiles growing under the other two conditions was limitedby the cell wall rigidity. A decrease in the relative amountof noncellulosic glucose of the cell wall, and an increase inthe noncellulosic xylose during coleoptile growth were foundfor all three culture conditions. ¹ Present address: Departamento de Fisiologia Vegetal, Facultadde Ciencias, Universidad, Salamanca, Spain. (Received May 21, 1979; )     

Growth and cell wall changes in rice coleoptiles growing under different conditions II. Auxin-induced growth in coleoptile segments

The effect of auxin on growth, mechanical properties of thecell wall and cell wall sugar composition in rice coleoptilesegments excised at different ages from seedlings growing underdifferent conditions were investigated. Auxin markedly inducedgrowth only in segments excised from coleoptiles in the fastgrowth phase with a high content of non cellulosic glucose intheir cell walls. The response to auxin decreased with coleoptileage, accompanying a decrease in the amount of the noncellulosicglucose in the cell wall, suggesting a correlation between noncellulosicglucose content and growth capacity in response to auxin. Goodcorrelation among auxin-induced growth, auxin-induced decreasein the T_o value and auxin-induced decrease in the noncellulosicglucose content of the cell wall also was found. ¹ Present address: Departamento Fisiologia Vegetal, Facultadde Ciencias, Universidad de Salamanca, Salamanca, Spain. (Received May 21, 1979; )     

Mutation in mce operons attenuates Mycobacterium tuberculosis virulence

On the Mycobacterium tuberculosis genome there are four mce operons, all of which are similar in sequence and organization, and code for putatively exported proteins. To investigate whether Mce proteins are essential for virulence, we generated knock-out mutants in mce1, mce2 and mce3 operons of M. tuberculosis and evaluated their ability to multiply in a mammalian host. The allelic replacement was confirmed in each mutant strain by Southern blotting. RT-PCR experiments demonstrated the lack of in vitro expression of mutated genes in Deltamce1 and Deltamce2 mutants. On the other hand, no expression of mce3 was detected in either the wild-type or mutant strains. Similar doubling time and growth characteristics in in vitro culture were observed for mutants and parental strains. The intratracheal route was used to infect BALB/c mice with the Deltamce3, Deltamce2 and Deltamce1 mutants. Ten weeks after infection, all mice infected with the Deltamce mutants survived, while those infected with the wild-type strain died. This long survival correlated with very low counts of colony-forming units (CFU) in the lungs. Deltamce1-infected mice developed very few and small granulomas, while animals infected with Deltamce3 or Deltamce2 mutants showed delayed granuloma formation. Mice infected with Deltamce1 did not develop pneumonia, while animals infected with Deltamce3 and Deltamce2 mutants showed small pneumonic patches. In spleens, bacterial counts of mutant strains were less reduced than in lungs, compared with those of wild-type. In contrast, no such attenuation was observed when the intraperitoneal route was used for infection. Moreover, Deltamce1 mutants appear to be more virulent in lungs after intraperitoneal inoculation. In conclusion, mce operons seem to affect the virulence of M. tuberculosis in mice, depending on the route of infection. Hypotheses are discussed to explain this last issue. Thus, mutants in these genes seem to be good candidates for vaccine testing.     

Integrated outdoor culture of two estuarine macroalgae as biofilters for dissolved nutrients from <Emphasis Type="Italic">Sparus auratus</Emphasis> waste waters

An integrated outdoor cultivation of two macroalgal species: Ulva rotundata (Chlorophyta) and Gracilariopsis longissima (Rhodophyta) was designed. The macroalgae were cultured in effluents from an intensive marine culture (growout phase) of gilthead seabream Sparus aurata. The biomass evolution of the algal tanks followed a logistic curve, where the approach to the maximum stocking density of seaweeds was governed by thalli self-shading, as nutrient limitation in the cultivation tank was unlikely. The maximum stocking density of the system was approximately 27.8 g U. rotundata L⁻¹ (16.7 Kg m⁻²) and 11.9 g G. longissima L⁻¹ (7.12 Kg m⁻²). Yield was more than 3 times higher in U. rotundata than in G. longissima. Overall, U. rotundata removed a greater percentage of phosphate (8.9%) and total dissolved inorganic nitrogen (54%) flowing into the algal tanks than G. longissima. The latter species biofiltered approximately 3.2% of phosphate and 17% of the total dissolved inorganic nitrogen input. However, mean nutrient uptake rates on wet weight basis were usually higher in G. longissima than in U. rotundata. The production of total oxidised nitrogen in the algal tanks, considered as being the nitrification rate occurring on the algal fronds by nitrifying bacteria, was less than half of the ammonium uptake by the macroalgae, suggesting that seaweeds competed efficiently for ammonia against the nitrifyers. The biofiltration during a diel cycle showed that mean phosphate biofiltration was lower than 4.5% in the two species whereas ammonium was biofiltered efficiently (up to 67%), especially in U. rotundata. The metal and heavy metal content in the algal tissue at the end of the monitoring period suggested no metal contamination of tissues so that both macroalgal species could be used in the food industry. The study reveals the value of ecological engineering techniques in reducing the dissolved nutrient content in effluents from the fish farm, with the prospect of a better management practises, based on integrated mariculture designs, being developed by the local farmers.     

Expression of a xyloglucan endotransglucosylase/hydrolase gene, Mt-XTH1, from Medicago truncatula is induced systemically in mycorrhizal roots

Xyloglucan endotransglucosylase/hydrolases (XTH) are enzymes that catalyze the hydrolysis and transglycosylation of xyloglucan polymers in plant cell walls. Previously, we isolated a cDNA from mycorrhizal roots of Medicago truncatula that is predicted to encode an XTH [van Buuren, M.L., Maldonado-Mendoza, I.E., Trieu, A.T., Blaylock, L.A., Harrison, M.J., 1999. Novel genes induced during an arbuscular mycorrhizal (AM) symbiosis between M. truncatula and G. versiforme. Mol. Plant-Microb. Interact. 12, 171-181.]. Here, we identified the corresponding XTH gene, designated Mt-XTH1. The Mt-XTH1 gene contains four exons separated by three introns and resides on a 15-kb Xba1 fragment adjacent to a second XTH gene designated Mt-XTH2. Mt-XTH2 shares the same exon-intron structure as Mt-XTH1. Exons 2, 3 and 4 and introns 1 and 2 are identical to Mt-XTH1, while exon 1 and intron 3 are divergent, both in sequence and in length. Mt-XTH1 is induced following colonization of the roots by AM fungi but does not respond to changes in phosphate status. Analysis of transgenic roots expressing an Mt-XTH1 promoterColon, two colonsuidA fusion revealed that the Mt-XTH1 promoter directs expression in cells throughout the root system with significantly higher levels of activity in mycorrhizal roots. Mt-XTH1 expression is elevated not only in the regions of the roots colonized by the fungus, but also at sites distal to the infected regions. These expression patterns are consistent with activation in response to a systemic signal.     

An efficient expression system for the production of functionally active human LKB1

Human LKB1, also known as STK11, is a tumour-suppression protein that mediates important functions in cellular proliferation and polarization. It might constitute an important target in cancer therapy. In order to produce large amounts of recombinant protein for biochemical and functional studies, a full-length cDNA clone was subcloned and expressed in Escherichia coli and insect cells. Although fusion proteins corresponding to LKB1 with 6xHis, GST and MBP tags could be overexpressed in E. coli, only MBP-LKB1 was recovered in a soluble, but heavily degraded form. Further studies demonstrated that this protein was not functional. Subsequent expression in insect cells of LKB1 with 6xHis and GST tags yielded insoluble products also. However, when chaperones Hsp70 and its cofactors Hsp40 and Hsdj were co-expressed with GST-LKB1, a clear increase in the solubility of the final protein was obtained. Moreover, this soluble, purified recombinant GST-LKB1 demonstrated to be a phosphoprotein, with at least residue Ser325 phosphorylated. The purified protein was functionally active as being able to demonstrate autophosphorylation in the absence of any associated kinase.