Lipolytic and peroxidative enzyme expressions in cultured potato tuber cells

Potato cells (cv. Norchip) were cultured from tuber parenchymal tissue and subcultured to dissociate and habituate the despecialized cells. After several subculturings on a minimal nutrient media, this line of cells demonstrated repeatable physical growth profiles for dry weight (DW), fresh weight (FW) and protein. Two enzymes of plant lipid metabolism were investigated, lipolytic acyl hydrolase (LAH) and lipoxygenase (LOX), which respectively liberate and peroxidize fatty acids from lipid in cellular membranes. LAH, measured as p-nitrophenyl palmitate hydrolase, was present in this line of cells in easily detectable amounts (317 units g^-1 DW) albeit much lower than that found in mother tuber (9878 units g^-1 DW). The presence of LAH in this line is significant because LAH isozymes are often described as storage proteins, yet activity per gram fresh weight in these unorganized cells is reasonably constant until culture growth exits the linear phase. However, LOX, the most active free fatty acid metabolizing enzyme in potato tubers (89,800 units g^-1 DW), was not detectable in this line of callus or suspension cultured cells. The absence of LOX activity in this line of cells was verified by a number of assay approaches and was confirmed by activity staining of extracted enzymes separated in polyacrylamide gels. The absence of LOX in these cultured cells is especially important in determining the functions of this lipid peroxidation system and how it may be genetically regulated.Mention of company or trade name does not imply endorsement by the United States Department of Agriculture over others not named.A laboratory cooperatively operated by the Midwest Area, Agricultural Research Service, U.S. Department of Agriculture, The Minnesota Agricultural Experiment Station, the North Dakota Agrcultural Experiment Station, and the Red River Valley Potato Grower's Association.     

Distribution and breeding biology of offshore cichlids in Lake Malawi/ Niassa

Synopsis Lake Malawi/Niassa is the second largest rift valley lake in Africa, with an area of 28 800 km², and an average and maximum depth of 292 m and>700 m, respectively. The lake is well known for the great diversity of fish occurring in the inshore zone. However, the offshore fish community is poorly documented. To rectify this, regular sampling was undertaken over two years, using trawl and gillnets at six offshore locations. This paper reports on the species composition, spatial distribution and breeding biology of the dominant cichlids species from the offshore pelagic zone. Cichlids formed approximately 88% of the offshore fish biomass. Most abundant were two species of zooplanktivores in the genus Diplotaxodon that made up 71% of the offshore fish biomass. An undescribed species, given the cheironym D. bigeye, was mainly found at a depth of 220 m during the day, but moved into near surface waters at night when the moon was full. This species was absent from the shallow regions of the lake. The most abundant offshore species was D. limnothrissa, which was distributed evenly throughout the lake to depths of 220 m. A less common offshore zooplanktivore was Copadichromis quadrimaculatus that formed 5% of the biomass and was confined to the upper 100 m of the water column. The main piscivores were in the genus Rhamphochromis and formed approximately 10% of the offshore fish biomass. The two dominant taxa were R. longiceps and the large Rhamphochromis group, and both were more common in the southern half of the lake. The former occurred mainly in the upper 100 m of the water column and the latter mainly at depths of 100–150 m. The length at maturity and fecundity for the dominant offshore species were estimated and seasonal breeding cycles determined from gonad activity and gonado-somatic indices.     

Transforming growth factor-beta: Its effect on phenotype reexpression by dedifferentiated chondrocytes in the presence and absence of osteogenin

Summary The single and combined actions of transforming growth factor (TGF)-beta and osteogenin were evaluated with regard to induction of colony formation and reexpression of the differentiated phenotype by dedifferentiated rabbit articular chondrocytes in soft agarose under serum-free conditions. TGF-beta alone did not promote colony formation and induced accumulation of proteoglycans and type II collagen at significantly lower levels than those induced by osteogenin. Although synergism between these two growth factors occurred with respect to the induction of colony formation, their joint action on reexpression of the differentiated phenotype was additive. Complex interactions between the two growth factors may explain the latter phenomenon.     

Actin acetylation in Drosophila tissue culture cells

In a permanent cell line derived from Drosophila embryos, cytoplasmic actin is produced as an unstable precursor, which is subsequently converted to a stable form. This conversion results in a reduction in isoelectric point, with no apparent change in molecular weight. The conversion involves an enzymatic acetylation, and results in an insensitivity to aminopeptidase digestion, suggesting N-terminal blockage. Both the acetylated and unacetylated actins can participate in the assembly of F-actin, but with different efficiencies.This work was supported by a grant from the NIH (GM 22866).     

Chlorophyll reduction in the seed of Brassica napus with a glutamate 1-semialdehyde aminotransferase antisense gene*

Chlorophyll reduction in the seed of Brassica can be achieved by downregulating its synthesis. To reduce chlorophyll synthesis, we have used a cDNA clone of Brassica napus encoding glutamate 1-semialdehyde aminotransferase (GSA-AT) to make an antisense construct for gene manipulation. Antisense glutamate 1-semialdehyde aminotransferase gene (Gsa) expression, directed by a Brassica napin promoter, was targeted specifically to the embryo of the developing seed. Transformants expressing antisense Gsa showed varying degrees of inhibition resulting in a range of chlorophyll reduction in the seeds. Seed growth and development were not affected by reduction of chlorophyll. Seeds from selfed transgenic plants germinated with high efficiency and growth of seedlings was vigorous. Seedlings from T₂ transgenic lines segregated into three distinctive phenotypes: dark green, light green and yellow, indicating the dominant inheritance of Gsa antisense gene. These transgenic lines have provided useful materials for the development of a low chlorophyll seed variety of B. napus.     

Biosynthesis of modified peptidoglycan precursors by vancomycin-resistant Enterococcus faecium

In the presence of bacitracin, vancomycin-resistant Enterococcus faecium (vanA phenotype) accumulate UDP-N-acetylmuramyl(UDP-Mur-NAc)-tetrapeptide and a UDP-MurNAc-depsipentapeptide containing lactate substituted for the carboxy-terminal-D-alanine residue. In an in vitro peptidoglycan polymerization assay, the modified precursors function and confer resistance to vancomycin.     

GEOTAXIS/PHOTOTAXIS AND BIOCHEMICAL PATTERNS IN HETEROCAPSA (=CACHONINA) ILLDEFINA (DINOPHYCEAE) DURING DIEL VERTICAL MIGRATIONS

Two separate experiments with Heterocapsa (= Cachonina ) illdefina Herman et Sweeney, one with and the other without water volume replacement, were performed in a 250-L laboratory mesocosm (45-cm diameter × 150-cm height) to examine how diel vertical migration (DVM) relates to taxis sign and strength and to cellular biochemical state. Although only the cell population grown with water volume replacement maintained a division per day over the course of the experiment, periodic measurements during both experiments demonstrated that cells aggregating at the surface during the light period generally were deficient in all measured biochemical constituents compared to cells obtained from a midcolumn depth. More specifically, H. illdefina cells that aggregated at the surface during the light period in both experiments exhibited weakened positive geotaxis but strengthened positive phototaxis and were very deficient in lipid and free amino acid compared to midcolumn cells. Cells sampled at midcolumn during the light period exhibited similar but weaker taxes changes compared to surface samples, and geotaxis strength was inversely correlated with cell diameter, cellular DNA and protein content, and RNA/DNA ratio. In comparison, published data on Gymnodinium breve Davis, a harmful algal bloom species, showed that cells aggregating at the surface during the light period generally exhibited weakened negative geotaxis and strengthened positive phototaxis and were very deficient in lipid and chl a compared to midcolumn cells. Although the persistent tendency toward negative geotaxis was weaker in midcolumn subpopulations throughout the day, its strength was inversely correlated with cell diameter and cellular lipid content. The combined results for both species support a revised conceptual model of optimized DVM in autotrophic marine dinoflagellates incorporating generalized expressions of taxis and biochemical state of individual cells.     

Ascorbic acid improves conversion of white spruce somatic embryos

Summary The effects of exogenous applications of ascorbic acid on white spruce somatic embryogenesis were examined. Increasing concentrations of ascorbate (1 μM to 100 μM) in the germination medium enhanced somatic embryo conversion in a linear fashion. At the optimal ascorbate level (100 μM) the number of embryos able to undergo normal conversion, i.e., emergence of both root and shoot, increased from 34% (control) to 58%. The effect of ascorbate had a more pronounced effect on shoot growth than on root emergence; and at 100 μM ascorbate, the percentage of embryos able to produce new leaf primordia increased from 47% (control) to 79%. Root emergence increased slightly from 64% in the control embryos to 74% in the presence of ascorbic acid. The ascorbate-treated embryos were characterized by an enlarged apical region, presumably due to a larger number of leaf primordia produced, and by dark green leaves. When allowed to grow further, these embryos were able to develop into normal plantlets.     

Sedimentary records of accelerated nutrient loading in Florida lakes

Transfer functions relating trophic state (Carlson's TSI_{chlorophyll-a}) to present day accumulation rate of (1) nutrients, (2) cations, and (3) organic sediment, are computed using Binford's ²¹⁰Pb-dilution method. As computed from surficial sediments of 27 lakes, former trophic states are reconstructed for recent (²¹⁰Pb-dated) sedimentary histories of 14 lakes. Of the three kinds of models potentially available, model (3) (TSI vs. organic accumulation) is the weakest statistically, and may be unduly influenced by exceptional deposition and/or preservation of allochthonous organic matter. At present, however, it is the only model applicable to all 14 of the histories tested. Results are encouraging in that model accurately predicts observed TSI's in several mesotrophic and eutrophic lakes. Clearly significant increases (accelerations) are inferred only for a of the most eutrophic lakes of the set, while the model consistently overpredicts TSI's of the 7 most oligotrophic lakes. As Whitmore's diatom-assemblage index is a better predictor of TSI than is model (3) in the one eutrophic lake in which it has been tested, we expect more persuasive results when models (1) and (2) can be tested within a more complete set of analytical data. We were surprised to find 3 severely disturbed lakes among the 12 that show little or no acceleration in rate of eutrophication in recent decades, but we defer attempts at explanation until former nutrient loading can be tested by model (1).     

Acquired resistance in dogs to repeated infestation with Ixodes scapularis (Acari: Ixodidae) reduces tick viability and reproductive success

The purpose of this study was to determine whether dogs develop acquired resistance to adult Ixodes scapularis infestation in an experimental model. Five dogs were each infested with ten mating pairs of ticks every week for 7 consecutive weeks, another five dogs were each infested with ten mating pairs once every 2 weeks for 10 weeks and four dogs served as controls not exposed to ticks. All ticks were allowed to feed to repletion and were collected only after dropping from the host. Several variables were measured to determine the extent of blood feeding success. Regression analysis indicated that the engorgement success, survival and mean tick engorgement weight declined with repeated infestation in both groups of dogs (p<0.05). Tick oviposition as well as the F1 viability declined with each successive infestation in both groups. These results suggest that repeated infestation with I. scapularis elicits a protective immune response against tick feeding and could serve as a limiting factor in the spread and transmission of Borrelia burgdorferi.