Importance of canopy structure on photosynthesis in single- and multi-species assemblages of marine macroalgae

Plant communities utilize available irradiance with different efficiency depending not only on their photosynthetic characteristics but also on the canopy structure and density. The importance of canopy structure are well studied in terrestrial plant communities but poorly studied in aquatic plant communities. The objective of this study was to evaluate macroalgal community photosynthesis in artificial constructed communities of one to four species with different morphologies along a range of leaf (i.e.=thallus) area densities. In a laboratory set-up we measured net photosynthesis and dark respiration in constructed assemblages of macroalgae, excluding effects other than photosynthesis of individual tissue and distribution of photons in the canopy from influencing metabolism. We hypothezised that 1) canopy structure determines the actual rates of photosynthesis relative to the optimal rates and 2) multi-species communities attain higher maximum photosynthetic rates than single species communities. We found that differences in canopy structure outweighed large differences in tissue photosynthesis resulting in relatively similar maximum community photosynthetic rates among the different single and multi-species assemblages (20.1–40.5 μmol O₂ m⁻² s⁻¹). Canopy structure influenced community photosynthesis both at low and high leaf area densities because it determines the ability of macroalgae to use the photosynthetic potential of their individual tissues. Due to an averaging effect the photosynthetic rate at high leaf area density was more similar among multi-species community than among single-species communities. Multi-species communities had, on average, a slightly higher photosynthetic production than expected from photosynthesis of single species communities. Moreover multi-species communities were capable of exposing new tissue to irradiance up to high densities thereby avoiding a decrease in net photosynthesis. This finding suggests that multi-species communities may be able to maintain higher biomass per unit ground area than single-species communities.     

Sequence and characterisation of a ribosomal RNA operon fromAgrobacterium vitis

One of the four ribosomal RNA operons (rrnA) from theAgrobacterium vitis vitopine strain S4 was sequenced.rrnA is most closely related to therrn operons ofBradyrhizobium japonicum andRhodobacter sphaeroides and carries an fMet-tRNA gene downstream of its 5S gene, as in the case ofR. sphaeroides. The 16S rRNA sequence of S4 differs from theA. vitis K309 type strain sequence by only one nucleotide, in spite of the fact that S4 and K309 have very different Ti plasmids. The predicted secondary structure of the S4 23S rRNA shows several features that are specific for the alpha proteobacteria, and an unusual branched structure in the universal B8 stem. The 3′ ends of the three otherrrn copies of S4 were also cloned and sequenced. Sequence comparison delimits the 3′ ends of the four repeats and defines two groups:rrnA/rrnB andrrnC/rrnD.     

Novel cyanoguanidines with potent oral antitumour activity

4-Pyridyl cyanoguanidines with hydrophobic aromatic side chains showed potent antiproliferative activity in the human breast and lung cancer cell lines MCF-7, NYH and H460. In vivo, treatment with N-(6-chlorophenoxyhexyl)-N′-cyano-N″-4-pyridylguanidine (18, 20 mg/kg/day po.), gave a complete remission of tumours in a model of NYH inoculated nude mice.     

Reduction of lactoperoxidase-H2O2 compounds by ferrocyanide: indirect evidence of an apoprotein site for one of the two oxidizing equivalents

The titration by ferrocyanide and the localization of the oxidizing equivalents of lactoperoxidase "compound II" were studied as a function of pH. It was demonstrated that 1) whatever the pH, the structure of lactoperoxidase "compound II" was compatible with a Fe IV R degree state, 2) at acidic pH, ferrocyanide preferentially reduced the oxidizing equivalent localized on the heme iron to give an Fe III R degree compound, 3) at pH 4.2 only the Fe III R degree form was obtained after reduction of lactoperoxidase "compound II" with one mole of ferrocyanide and whereas at pH greater than 4.2, a mixture of both Fe III R degree and Fe IV R forms was present, 4) lowering the pH from 7.2 to 4.0 induced a transition of Fe IV R state to Fe III R degree state, but increasing the pH from 4.0 to 7.2 did not permit the formation of Fe IV R compound from Fe III R degree compound.     

Secondary structure of mouse 28S rRNA and general model for the folding of the large rRNA in eukaryotes.

We present a secondary structure model for the entire sequence of mouse 28S rRNA (1) which is based on an extensive comparative analysis of the available eukaryotic sequences, i.e. yeast (2, 3), Physarum polycephalum (4), Xenopus laevis (5) and rat (6). It has been derived with close reference to the models previously proposed for yeast 26S rRNA (2) and for prokaryotic 23S rRNA (7-9). Examination of the recently published eukaryotic sequences confirms that all pro- and eukaryotic large rRNAs share a largely conserved secondary structure core, as already apparent from the previous analysis of yeast 26S rRNA (2). These new comparative data confirm most features of the yeast model (2). They also provide the basis for a few modifications and for new proposals which extend the boundaries of the common structural core (now representing about 85% of E. coli 23S rRNA length) and bring new insights for tracing the structural evolution, in higher eukaryotes, of the domains which have no prokaryotic equivalent and are inserted at specific locations within the common structural core of the large subunit rRNA.     

Biochemical evidence for the non-inactivation of the steroid sulfatase locus in human placenta and fibroblasts

Summary Steroid sulfatase activities are significantly higher in placentas obtained after the birth of girls than after the birth of boys, and also in female fibroblasts compared to male strains. This constitutes biochemical evidence for the non-inactivation of the X-linked sulfatase locus. No hydrolytic activity is found in the fibroblasts of ichthyotic boys. Heterozygosity is demonstrated in the fibroblasts of the four mothers studied, as they have steroid sulfatase activity of less or equivalent to the normal male value.     

Myrosin cells and dilated cisternae of the endoplasmic reticulum in the order Capparales

Ultrastructural results for different types of protein–rich cells in five families generally accepted as Capparalean (Brassicaceae, Capparaceae, Resedaceae, Tovariaceae and Moringaceae) and two others (Gyrostemonaceae and Bataceae) considered by some workers to be Capparalean, support their alignment in the order Capparales. The term myrosin cell is used for those protein–rich cells which are typically idio–blastic and characterized by a homogenous, granular proteinaceous material in the vacuole and a cytoplasm which is filled with an extensive rough endoplasmic reticulum. This idioblastic myrosin cell type is characteristic for the Brassicaceae, Capparaceae, Tovariaceae, Moringaceae and Gyrostemonaceae. The guard cells of stomata may appear as myrosin cells, in which case they are termed guard–cell myrosin cells; they are found in the Resedaceae, Tovariaceae and Bataceae. Other proteinaceous cells are those with protein–rich dilated cisternae (DC) of the endoplasmic reticulum (ER). One type is the organelle–like DC, utricular or irregular dilations of the ER, filled with protein and ribosome–studded. Utricular DC are characteristic for the Brassicaceae and Capparaceae. Another type of DC is represented by protein–containing vacuoles derived from the ER, protein–rich ER–dependent vacuoles; these are found in the Brassicaceae, Capparaceae, Resedaceae, Tovariaceae and Gyrostemonaceae. The myrosin cells and cells with protein–rich dilated cisternae are here regarded as taxonomic criteria for the order Capparales.     

Factors controlling nitrification and denitrification: A laboratory study with gel-stabilized liquid cattle manure

Nitrification and denitrification were studied in a millimeterscale microenvironment using a two-phase system with a liquid manure-saturated layer. Samples consisted of liquid cattle manure and air-dried soil stabilized with silica gel, placed between two aerobic soil phases with a water content near field capacity. A high potential for NH₄ ⁺ oxidation developed within 0–2 mm distance from the interface, and NH₄ ⁺ diffused only 10–20 mm into the soil. Some NH₄ ⁺ was probably immobilized by microorganisms in the soil between 0 and 4 days, after which nitrification was the only sink for NH₄ ⁺. A potential for denitrification developed within the manure-saturated zone. Maximum rates of both potential and actual denitrification were recorded by Day 4, but denitrification continued for at least 2–3 weeks. The potential for nitrification peaked after 14 days. When the pH of the manure was adjusted to 5.5, nitrification was reduced close to the interface, and NH₄ ⁺ penetrated further into the soil before it was oxidized. The pH adjustment had an inhibitory effect on denitrification: Both potential and actual rates of denitrification were almost eliminated for several days. The size of the manure-saturated layer strongly affected denitrification losses. With layers of 8 and 16 mm thickness, losses equivalent to 33 and 40% of the original NH₄ ⁺ pool, respectively, were estimated. When manure corresponding to a 12 mm layer was homogeneously mixed with the soil, only 0.3% was lost.Offprint requests to: S. O. Petersen.     

Sequence and secondary structure of mouse 28S rRNA 5''terminal domain. Organisation of the 5.8S-28S rRNA complex.

We present the sequence of the 5' terminal 585 nucleotides of mouse 28S rRNA as inferred from the DNA sequence of a cloned gene fragment. The comparison of mouse 28S rRNA sequence with its yeast homolog, the only known complete sequence of eukaryotic nucleus-encoded large rRNA (see ref. 1, 2) reveals the strong conservation of two large stretches which are interspersed with completely divergent sequences. These two blocks of homology span the two segments which have been recently proposed to participate directly in the 5.8S-large rRNA complex in yeast (see ref. 1) through base-pairing with both termini of 5.8S rRNA. The validity of the proposed structural model for 5.8S-28S rRNA complex in eukaryotes is strongly supported by comparative analysis of mouse and yeast sequences: despite a number of mutations in 28S and 5.8S rRNA sequences in interacting regions, the secondary structure that can be proposed for mouse complex is perfectly identical with yeast's, with all the 41 base-pairings between the two molecules maintained through 11 pairs of compensatory base changes. The other regions of the mouse 28S rRNA 5'terminal domain, which have extensively diverged in primary sequence, can nevertheless be folded in a secondary structure pattern highly reminiscent of their yeast' homolog. A minor revision is proposed for mouse 5.8S rRNA sequence.