BIOMASS AND DYNAMICS OF GROWTH OF ULVA SPECIES IN PALMONES RIVER ESTUARY1

During the last decade, the Palmones River estuary has undergone severe eutrophication followed by a green tide episode; two species of Ulva, rotundata Blid. and Ulva curvata (Kütz.) De Toni, were the main macroalgae responsible for this bloom. From November 1993 to December 1994, we followed the biomass, the growth dynamics, and tissue elemental composition (C:N:P)of Ulva species, as well as some physicochemical variables in the estuary. Maximum biomass (up to 375 g dry wt·m^?2 in some spots, corresponding to a thallus area index of nearly 17 m²Ulva·m^?2 sediment) were observed in June and December. However, the biomass varied among the sampling stations. Water nitrate, ammonia, and phosphate showed high concentrations throughout the year, with extremely high transient pulses, sustaining the high growth rates observed. Growth rates were estimated directly in the field. The rates were generally higher in Ulva discs maintained in net cages than those estimated by changes in biomass standing stock between two consecutive samplings. The difference between both estimates was used to quantify the importance of the processes causing loss of biomass, which were attributable to grazing, exported biomass, and thallus decomposition under anaerobic conditions resulting from extreme self-shading. Maximum chlorophyll content was found in winter, whereas the minimum was in spring. Atomic N:P ratios were generally higher in the algae than in the water. However, the absolute concentrations of tissue N and P were always higher than the critical levels for maximum growth, which suggests that growth was not limited by inorganic N or P availability. The results suggested that the increase in nutrient loading in the river may have triggered the massive development of green algae and that light limitation and temperature stress in summer seem to be the main factors controlling the abundance of Ulva in the estuary. In addition to light availability and thermal stress, the different loss processes may have a decisive role in the dynamics of Ulva biomass.     

Correction of the beta-mannanase domain of the celC pseudogene from Caldocellulosiruptor saccharolyticus and activity of the gene product on kraft pulp.

The celA, manA, and celB genes from Caldocellulosiruptor saccharolyticus compose a cellulase-hemicellulase gene cluster and are arranged on a 12-kb C. saccharolyticus genomic fragment of the recombinant lambda bacteriophage NZP lambda 2. The beginning of a fourth open reading frame (celC) which was homologous to the C. saccharolyticus manA and celA genes was located at the 3' end of the 12-kb NZP lambda 2 genomic fragment. Genome-walking PCR was used to isolate DNA fragments downstream of the C. saccharolyticus celB gene, and the entire nucleotide sequence of celC was obtained. From the preliminary nucleotide sequence, celC appeared to encode yet another multidomain bifunctional enzyme (CelC) consisting of an N-terminal endo-1,4-beta-D-glucanase domain (75% similar to CelA domain 1), two central cellulose-binding domains, and a C-terminal endo-1,4-beta-D-mannanase domain (98% similar to ManA domain 1). However, upon completion of the celC sequencing, two -1 frameshifts were identified in the region encoding the putative CelC mannanase domain. The isolated CelC mannanase domain exhibited no beta-mannanase activity, which supported this observation. Recombinant PCR was used to correct the celC frameshifts by inserting the appropriate nucleotides into the gene. The repaired celC fragment containing the base insertions (manB) expressed strong beta-mannanase activity on soluble mannan substrates and showed significant activity on kraft pulp as judged by the release of reducing sugars.     

Plasmid rolling circle replication and its control

Abstract This review summarises current information on rolling circle replicating plasmids originally isolated from Gram-positive bacteria with a low guanine and cytosine content in their DNA. It focuses on the peculiar biological features of these small, high copy number plasmids that replicate via an asymmetric RC mechanism. The regulation of plasmid copy number is also discussed.     

The aspartate aminotransferase gene family of Arabidopsis encodes isoenzymes localized to three distinct subcellular compartments

Here, a complete study is described of all the genes and isoenzymes for aspartate aminotransferase (AspAT) present in Arabidopsis thaliana . Four classes of cDNAs representing four distinct AspAT genes ( ASP1—ASP4 ) have been cloned from Arabidopsis . Sequence analysis of the cDNAs suggests that the encoded proteins are targeted to different subcellular compartments. ASP1 encodes a mitochondrial form of AspAT, ASP3 encodes a chloroplastic/plastidic form of AspAT, whereas ASP2 and ASP4 each encode cytosolic forms of AspAT. Three distinct AspAT holoenzymes (AAT1—AAT3) were resolved by activity gel analysis. Organelle isolation reveals that AAT1 is mitochondrial-localized, AAT3 is plastid-localized, and AAT2 is cytosolic. Gene-specific Northern analysis reveals that each Asp mRNA accumulates differentially with respect to organ-type. However, the individual Asp mRNAs show no dramatic fluctuations in response to environmental stimuli such as light. Southern analysis reveals that four distinct nuclear genes probably represent the entire AspAT gene family in Arabidopsis . These molecular studies shed light on the subcellular synthesis of aspartate in Arabidopsis and suggest that some of the AspAT isoenzymes may play overlapping roles in plant nitrogen metabolism.     

The karyotype and ultrastructural characteristics of spontaneous preimplantation mouse parthenotes

Karyotypic and light and electron microscopical analyses were made of spontaneous preimplantation mouse parthenotes from the LT/Sv inbred strain. It was found that the activated oocyte and developing embryos were diploid. We believe that diploidization is achieved by the oogonium undergoing a premeiotic mitosis without cytokinesis followed by two meiotic divisions, thus producing diploid parthenotes. The developmental events with respect to membrane specialization, such as junctional complexes, were similar to those observed in fertilized embryos. A unique feature of the developing parthenote was the failure of the mitochondria to change during the morula stage. The mitochondria retained a few irregularly oriented cristae rather than many transversely oriented ones observed in morulae developing from fertilized eggs. The significance of this observation is discussed.     

Avian feather development: relationships between morphogenesis and keratinization

Morphogenesis and expression of the alpha and beta keratin polypeptides are controlled by epidermal-dermal interactions during development of avian skin derivatives. We have examined the relationship between morphogenesis of the embryonic feather and expression of the feather alpha and beta keratins by routine histology, indirect-immunofluorescence, and SDS-PAGE. Initially beta keratins are expressed only in the feather sheath. Following barb ridge morphogenesis beta keratins can be detected in the barb ridge, coincident with the differentiation of barb ridge cells into eight distinct morphological types. Beta keratinization occurs in gradients; from feather apex to base, and from periphery of the barb ridge to the interior. The onset of beta keratinization in the barb ridges is paralleled by an increase in the major feather beta keratin polypeptides, as detected by SDS-PAGE. The alpha keratins are present in both the periderm and feather sheath at early stages of feather development, but become greatly reduced after hatching, when the down feather emerges from the sheath.     

Amino acid sequence of the phosphorylation site of isocitrate dehydrogenase fromEscherichia coli

InEscherichia coli, NADP⁺-specific isocitrate dehydrogenase (EC 1.1.1.42) may undergo a phosphorylation catalyzed by a cAMP-independent protein kinase, with a concomitant decrease in catalytic activity. In this report, we describe the purification and amino acid sequence of a³²P-labeled peptide obtained from in vivo³²P-labeled isocitrate dehydrogenase. The³²P-labeled peptide was isolated from a tryptic digest and found to contain seven amino acids, including a single serine residue. Following automated Edman degradation and reversephase high-pressure liquid chromatography of the phenylthiohydantoin-amino acids, the sequence of this peptide was established to be-Ser(P)-Leu-Asn-Val-Ala-Leu-Arg.     

The role of colicin receptors in the uptake of ferrienterochelin by Escherichia coli K-12.

The amino terminal sequences of the 4 caseins synthesized by translation of ovine mammary mRNAs in a wheat germ cell-free system have been investigated by automated Edman degradation. The 3 “calcium-sensitive” caseins (α_s1, α_s2 and β) and κ-casein were synthesized as precaseins with amino terminal hydrophobic extensions of 15 and 21 amino acid residues respectively, resembling “signal peptides” of other secretory proteins. The extra pieces of the 4 caseins, which start with a methionyl residue, end with an alanyl residue which may be one of the signals recognized by the mammary membrane-bound enzyme responsible for the specific cleavage of precaseins. The amino terminal extensions of α_s1, α_s2 and β-caseins show a high degree of homology suggesting that they have derived from a common ancestor.     

Concerted inhibition of NADP+-specific isocitrate dehydrogenase by oxalacetate and glyoxylate. I. Oxalomalate formation and stability, and nature of the enzyme inhibition.

Oxalacetate and glyoxylate are each weak inhibitors of NADP+-specific isocitrate dehydrogenase (threo-DS-isocitrate:NADP+ oxidoreductase (decarboxylating), EC 1.1.1.42)9 Together, however, they act in a concerted manner and strongly inhibit the enzyme. The rates of formation and dissociation of the enzyme inhibitor complex, and the rate of formation and the stability of the aldol condensation product of oxalacetate and glyoxylate, oxalomalate, were examined. The data obtained do not support the often suggested possibility that oxalomalate, per se, formed non-enzymatically in isocitrate dehydrogenase assay mixtures containing oxalacetate and glyoxylate, is responsible for the observed inhibition of the enzyme. Rather, the data presented in this communication suggest that oxalacetate binds to the enzyme first, and that the subsequent binding of glyoxylate leads to the formation of a catalytically inactive enzyme-inhibitor complex.     

Variation of mitochondrial volume fraction along multiply innervated fibers in rabbit extraocular muscle

Mitochondrial volume fraction was compared among three regions along the length of six multiply innervated fibers (MIFs) in the orbital surface layer of rabbit superior rectus. These MIFs are of about 5 μm diameter toward the middle of their length, and of about 15 μm diameter toward their proximal and distal ends. The region of highest volume fraction (26%) was located toward the proximal end of their segment of minimal diameter, in apparent association with endplate-like nerve junctions. The region of lowest volume fraction (8%) was located at their distal segment of maximal diameter. The region toward the distal end of their segment of minimal diameter displayed an intermediate volume fraction (15%). These mitochondrial volume fractions were further analyzed in terms of the relative contributions of the I-band, the A-band, and the subsarcolemmal mitochondrial clusters. Comparable changes in mitochondrial content occur in both the I-band and A-band: in the fibers' distal segment of maximal diameter, however, the mitochondrial volume fraction in the A-band (5%) is lower than in the I-band (11%). These modifications of mitochondrial content along the fibers' length occur irrespective of the contributions of the subsarcolemmal mitochondrial clusters.