The effect of nitrate supplementation on the biochemical composition of benthic diatoms and the growth and survival of post-larval abalone

Elevating the nitrogen concentration in microalgal growth media can elevate the protein content of the algae and consequently increase their dietary value to molluscs. This study examined the protein content, and dietary value to abalone post-larvae, of seven benthic diatoms acclimated to high-(“H” = 49.4 mg NO₃-N l^− 1) and standard-nitrate (“S” = 16.5 mg NO₃-N l^− 1) Walne medium. In Experiment 1, the level of nitrate in the culture medium did not significantly affect the protein content of Cocconeis sp., Cylindrotheca closterium or Nitzschia ovalis, and variation in the growth of post-larval Haliotis iris was not associated with nitrate level or the protein content of the diatoms. When the same six diatom diets were added daily as cell suspensions, growth and survival were much lower than for the equivalent strains fed as established films (P < 0.0001). In Experiment 2a, the protein content of Navicula incerta was elevated by nitrate supplementation, and the high nitrate strain retained a higher protein content (P = 0.005) even after 24 days growing in unenriched, flowing seawater. Haliotis rufescens post-larvae grew significantly faster when fed N. incerta H than when fed N. incerta S (P = 0.006) and survival was also higher with this diet (67 versus 54%). In Experiment 2b, there was no significant effect of nitrate level on protein content of four diatoms or the performance of post-larval H. rufescens. There was, however, a strong positive correlation (r = 0.95, P < 0.0001) between post-larval survival and the lipid content of the diatom diets. Post-larval growth showed positive, but marginally non-significant, relationships with diatom protein and carbohydrate, but no relationship with lipid content. Overall, only one of seven benthic diatom species acclimated to high-nitrate growth medium displayed significantly elevated protein content. Diatom protein content explained relatively little of the variation in food value of diatom strains for post-larval abalone but lipid content correlated strongly with post-larval survival.     

The proximate composition and glycoalkaloid content of three potato meals

The proximate composition and glycoalkaloid content of a dried potato by-product meal (tater meal) and two dried potato pulp meals (potato meal and potato meal plus 10% molasses) were determined. All three feeds demonstrated variable compositions: the tater meal averaged 8.7% moisture, 9.1% crude protein, 5.4% ether extract, 5.0% crude fiber, 4.1% ash and 56.8% nitrogen-free extract; the potato meal averaged 14.5% moisture, 6.0% crude protein, 0.5% ether extract, 9.5% crude fiber, 2.2% ash and 57.1% nitrogen-free extract; the potato meal plus 10% molasses averaged 15.3% moisture, 6.4% crude protein, 0.3% ether extract, 8.0% crude fiber, 2.6% ash and 57.8% nitrogen-free extract. The phosphorus concentration was determined to be approximately 0.2% for the three samples. Other minerals were found in lesser concentrations. The riboflavin and thiamine concentrations of the three potato meals were less than 10% of the values reported for raw potato pulp and peel. The niacin concentration was approximately 40% of the values reported for raw potato pulp and peel. Tater meal contained 11.5 mg a-chaconine and 6.5 mg α-solanine per 100g meal. Analysis of potato meal gave 15.8 mg α-chaconine and 7.8 mg α-solanine per 100g meal while the potato meal plus 10% molasses was found to contain 13.2 mg α-chaconine and 7.3 mg α-solanine per l00g meal.     

The extraction and partial purification of a rhamnosidase from Colorado potato beetle larvae (Leptinotarsa decemlineata (Say))

An enzyme which hydrolyzed a terminal rhamnose moiety from α-chaconine was extracted and partially purified from Colorado potato beetle (CPB) (Leptinotarsa decemlineata) larvae. This ammonium sulfate precipitated enzyme fraction resulted in nearly 97% metabolism of α-chaconine after a 144 hour incubation period at 42 C as determined by high performance liquid Chromatographic (HPLC) analysis. Approximately 81% of the metabolized α-chaconine was detected asβ ₂-chaconine. The isolated enzyme fraction from CPB larvae exhibited no metabolism of α-solanine. Metabolism was also followed over time by thin layer chromatography (tlc).     

Inhibition of acetyl cholinesterase by solanaceous glycoalkaloids and alkaloids

Seven solanaceous glycoalkaloids (α-chaconine, β₂-chaconine, α-solanine, dehydrocommersonine, commersonine, demissine and tomatine) and three alkaloids (solanidine, tomatidine and demissidine) were tested for their ability to inhibit acetyl cholinesterase in anin vitro system. Glycoalkaloids at concentrations of 33–41 parts per million (ppm) gave cholinesterase inhibition ranging from 4.2 to 26.8%. All three alkaloids had lower anticholinesterase (4.2 to 15.4%) than the seven glycoalkaloids, except for tomatine. Two well-known cholinesterase inhibitors, carbaryl, a carbamate insecticide and Guthion, an organophosphate insecticide, were also tested for comparison. It required only 1 to 2 ppm of the insecticides to give the same average percent inhibition as was observed with the glycoalkaloids at concentrations of 33–35 ppm.     

Enteric coronavirus infection in a juvenile dromedary (Camelus dromedarius).

A case of an enteric coronavirus infection in a 6-week-old dromedary calf is described. The animal had diarrhea for 5 days and died despite symptomatic treatment. Numerous viral particles, approximately 140 nm in diameter, with club-like projections were detected in the feces by electron microscopy. These characteristics were consistent with a coronavirus. Immunohistochemical reactivity with 2 antigenic group II coronavirus-specific antibodies confirmed the presence of viral antigen in colonic epithelial cells. The death of the animal was attributed to a neutrophilic and emphysematous colitis that likely was caused by an infection with a Clostridium sp.     

Acclimation of loblolly pine (Pinus taeda) seedlings to high temperatures

To determine the extent to which loblolly pine seedlings (Pinus taeda L.) acclimate to high temperatures, seedlings from three provenances-southeastern Texas (mean annual temperature 20.3 degrees C), southwestern Arkansas (mean annual temperature 16.2 degrees C) and Chesapeake, Maryland (mean annual temperature 12.8 degrees C)-were grown at constant temperatures of 25, 30, 35 or 40 degrees C in growth chambers. After two months, only 14% of the seedlings in the 40 degrees C treatment survived, so the treatment was dropped from the experiment. Provenance and family differences were not significant for most measured variables. Total biomass was similar in the 25 and 30 degrees C treatments, and less in the 35 degrees C treatment. Foliage biomass was higher, and root biomass lower, in the 30 degrees C treatment compared with the 25 degrees C treatment. Net photosynthesis and dark respiration of all seedlings were measured at 25, 30 and 35 degrees C. Both net photosynthesis and dark respiration exhibited acclimation to the temperature at which the seedlings were grown. For each temperature treatment, the highest rate of net photosynthesis was measured at the growth temperature. Dark respiration rates increased with increasing measurement temperature, but the basal rate of respiration, measured at 25 degrees C, decreased from 0.617 &mgr;mol m(-2) s(-1) in the 25 degrees C treatment to 0.348 &mgr;mol m(-2) s(-1) in the 35 degrees C treatment, resulting in less carbon loss in the higher temperature treatments than if the seedlings had not acclimated to the growth conditions. Temperature acclimation, particularly of dark respiration, may explain why total biomass of seedlings grown at 30 degrees C was similar to that of seedlings grown at 25 degrees C.     

Genetic variation for carbon isotope composition in honey mesquite (Prosopis glandulosa)

Carbon isotope composition (delta(13)C) is a useful surrogate for integrated, plant water-use efficiency (WUE) when measured on plants grown in a common environment. In a variety of species, genetic variation in delta(13)C has been linked to the distribution of genotypes across gradients in atmospheric and soil water. We examined genetic variation for delta(13)C in seedlings of honey mesquite (Prosopis glandulosa Torr.), an invasive grassland shrub that thrives in the southwestern USA. Fifteen maternal families, representing progeny of 15 adult trees, were studied in three common garden experiments in a greenhouse. The 990-km east-west transect along which the adult trees were located encompasses a wide precipitation gradient, and includes mesic grassland, semiarid grassland, and Chihuahuan desert ecosystems. Genetic variation for delta(13)C in mesquite was substantial, with the rank order of half-sib families based on delta(13)C relatively stable across experiments, which were conducted under different environmental conditions. Conversely, rankings of families by mean seedling height (an index of growth rate) varied markedly among experiments. Seedlings derived from Chihuahuan desert adults emerged more quickly and had more negative delta(13)C (indicative of lower WUE) than seedlings derived from the other regions. Although delta(13)C and seedling height were not correlated, these results suggest that mesquite genotypes at the drier, western extreme of the species' range are adapted for quicker emergence and possibly faster growth than genotypes from mesic areas. Together, these traits may facilitate exploitation of infrequent precipitation events.     

The effects of soil mixing on soil nutrient status,recovery of competing vegetation and conifer growth on cedar-hemlock cutovers in coastal British Columbia

In 1988 an experiment was established to stimulate the effect of windthrow on low-and high-productivity forest types in coastal British Columbia. It was hypothesized that site productivity may be improved by mixing the upper 1 m of the organic matter and mineral soil. Results of this study indicated that soil mixing (1) slightly increased soil pH and temperature on both forest types after 2 and 5 years, (2) decreased all soil nutrient availability indices on the high productivity type after 2 years, but resulted in no difference from the control after 5 years, and (3) decreased microbial activity and cellulose loss rate and most soil nutrient availability indices on the low-productivity type after 2 and 5 years. Soil mixing greatly reduced Gaultheria shallon above-ground biomass on both low- and high productivity forest types, whereas biomass of Epilobium angustifolium and other plant species increased slightly on the high-productivity type after 2 and 5 vears. Tsuga heterophylla was taller on high-productivity type and on mixed plots in both types after 2 and 5 years. Thuja plicata was taller on the high-productivity type after 5 years only. The increased conifer growth measured on the mixed low-productivity type was attributed to higher levels of available nutrients due to reduced G. shallon competition.     

Desiccation tolerance of rhizobia when protected by synthetic polymers

Survival of rhizobia applied to the surface of legume seeds is poor due to factors such as desiccation. Poor survival of rhizobia results in poor nodulation and yield of legumes. Selecting polymeric adhesives for inoculation of legume seed with rhizobia that provide protection during desiccation may improve survival and increase the potential for maximum legume yields. Vacuum-drying cells after suspension in selected polymers proved an effective method for screening the potential of polymers to improve the desiccation tolerance of rhizobia. The effect of different polymers on survival of desiccated rhizobia could be attributed to their different chemical and physical properties. The specific protective properties of polymers have been difficult to determine due to the variation in the chemical nature of polymers often compared. In this research polyvinyl alcohol (PVA) with varying degrees of hydrolysis provided a useful range of measurable physical properties against which bacterial survival could be measured. PVA with a percent hydrolysis in the range 86.5-89% was better able to protect desiccated cells of a range of rhizobial strains than polymers with higher (98.5%) or lower (78.5-82%) degrees of hydrolysis. The percent hydrolysis affected the moisture properties of PVA and survival of rhizobia was not maximised with high moisture sorption or low water activity by the polymer but rather when moisture properties were at an intermediate level. In comparison, survival was poorest in highly hygroscopic polymers methyl cellulose (MC) and polyvinyl pyrrolidone (PVP). The survival profile of desiccated rhizobia stored at different relative humidities was altered when cells were embedded in different polymers and is probably related to moisture sorption by those polymers. The percent hydrolysis also affects the extent to which PVA is able to stabilise colloids against the precipitating action of KCl. The colloid-stabilising property and survival was highest at 86.5-89% indicating that this property may be manipulated to achieve better survival. There is an indication that highly stabilising PVA may lead to more evenly dispersed cells providing more colony forming units rather than better survival. However, survival was not strongly correlated to the colloid-stabilising properties of the other polymers and was very poor after suspension in highly stabilising MC indicating a strong interaction between factors. Synthetic polymers designed to improve survival of rhizobia exposed to desiccation stress should include properties that combine high stabilisation and optimum moisture sorption properties.