An order-specific monoclonal antibody to Diptera reveals the impact of alternative prey on spider feeding behavior in a complex food web

Generalist predators have the capacity to restrict pest population growth, especially early in the season before densities increase. However, their polyphagous feeding habits sometimes translate into reduced pest consumption when they target alternative prey. An order-specific monoclonal antibody was developed to examine the strength of trophic connections between Diptera, a major category of non-pest prey, and linyphiid spiders in alfalfa. We report the development and characterization of a monoclonal antibody with order-level specificity to Diptera. This antibody elicited strong absorbance to 22 Diptera from 13 families, no false-positive reactivity to non-dipteran invertebrates, and antigen detection periods following prey consumption that were comparable between spiders. Over 900 field-collected females of the linyphiid spiders Erigone autumnalis and Bathyphantes pallidus were screened for Diptera antigen. Significantly more B. pallidus screened positive for Diptera (40%) compared to E. autumnalis (16%), indicating differential reliance on these prey. In parallel with the collection of spiders for gut-content analysis, prey availability was estimated at web sites. The two spiders exhibited different feeding responses to prey availability. Consumption of Diptera by B. pallidus was strongly correlated with Diptera abundance whilst the availability of other potential prey did not influence predation rates. Conversely, E. autumnalis did not prey upon Diptera in proportion to availability, but increased Collembola activity-density reduced dipteran consumption. Integration of molecular gut-content analysis with precise sampling of prey demonstrated how two closely related linyphiid spiders exhibit different feeding responses to the availability of prey under natural field conditions. Elucidating the feeding preferences of natural enemies is critical to effective incorporation of biological control by generalist predators in the management of agricultural pests.     

The control of CTP:choline-phosphate cytidylyltransferase activity in pea (Pisum sativum L.).

Several possible control mechanisms for CTP:choline-phosphate cytidylyltransferase (EC 2.7.7.15) activity in pea (Pisum sativum L.) stems were investigated. Indol-3-ylacetic acid (IAA) treatment of the pea stems decreased total cytidylyltransferase activity but did not affect its subcellular distribution. Oleate (2 mM) caused some stimulation of enzyme activity by release of activity from the microsomal fraction into the cytosol, but neither phosphatidylglycerol nor monoacyl phosphatidylethanolamine had an effect on activity or subcellular distribution. A decrease in soluble cytidylyltransferase protein concentrations was found in IAA-treated pea stems, but this was not sufficient to account for all of the decrease in cytidylyltransferase activity. A 50% inhibition of enzyme activity could be obtained with 0.2 mM-CMP, which indicated possible allosteric regulation. Similar inhibition was obtained with 1.5 mM-ATP, but other nucleotides had no effect. The cytidylyltransferase enzyme protein was not directly phosphorylated, and the inhibition with 1.5 mM-ATP occurred with the purified enzyme, thus excluding an obligatory mediation via a modulator protein. The results indicate that the cytosolic form of cytidylyltransferase is the most important in pea stem tissue and that the decrease in cytidylyltransferase activity in IAA-treated material appears to be brought about by several methods.     

ENZYMES OF PHOSPHOINOSITIDE METABOLISM DURING RAT BRAIN DEVELOPMENT

—The activities of four enzymes concerned with inositol lipid metabolism have been determined in homogenates of rat brains of different ages. The enzymes are CDP-diglyceride inositol phosphatidate transferase, phosphatidylinositol kinase, diphosphoinositide kinase and triphosphoinositide phosphomonoesterase. The activities of all the enzymes increased with age. Phosphatidylinositol kinase activity rose most sharply well before myelination, reaching a maximum at about 6 days of age. Diphosphoinositide kinase and triphosphoinositide phosphomonoesterase activities increased most rapidly during myelination. The increase in CDP-diglyceride inositol phosphatidate transferase showed no definite association with any period of development. It is concluded that triphosphoinositide metabolism is associated with myelin or a closely related structure.     

Flagellation of Pseudomonas putida and analysis of its motile behavior.

Pseudomonas putida flagella were examined. Also, changes in motile behavior in response to chemoattractants were analyzed quantitatively by computer. Reversals in the rotation direction of bundles of polar flagella resulted in changes in swimming direction. Cells swimming in buffer changed direction once every 2 s on average, whereas cells exposed to the attractant benzoate changed direction an average of once every 10 s. The findings show that P. putida responds to temporal gradients of chemoattractant by suppressing changes in the direction of rotation of flagella.     

A marine and terrestrial Sirius Group succession, middle Beardmore Glacier-Queen Alexandra Range, Transantarctic Mountains, Antarctica

A succession of Sirius Group glacigene sediments which crop out along the western margins of the Beardmore valley between Cherry Icefall and Hewson Glacier, below The Cloudmaker, is designated as the stratotype of the Cloudmaker Formation. This new formation overlies a multiply glaciated pavement (Dominion Erosion Surface) cut into the Precambrian Goldie Formation, and is disconformably overlain by the Meyer Desert Formation (Sirius Group). The Cloudmaker Formation comprises bedded and massive diamictons, bedded sands and silts, and laminated clays. Assemblages of foraminifera occur throughout the Cloudmaker Formation and indicate that these basal Sirius Group sediments were deposited in brackish glacial marine environments. The general absence of diatoms suggest these marine waters were ice-covered. Similar marine assemblages are also present in basal Sirius Group sediments at Oliver Bluffs, Dominion Range. Recycled marine diatom assemblages in the Sirius Group at the latter locality indicate that the host sediments have an age of < 3.8 Ma (Pliocene). The Cloudmaker Formation is placed in the Pliocene, although a latest Miocene age for the basal sediments cannot be ruled out.Stratigraphie, sedimentologic, and paleontologic evidence suggests that Beardmore valley was occupied by a fjord and tidewater glacier system that extended at least 165 km through the Transantarctic Mountains from the southwestern Ross Sea. The stratigraphy of The Cloudmaker Formation consists of a succession of members separated by disconformities. It is hypothesised that these strata were deposited by a dynamic valley glacier system that underwent a history of glacier advance and grounding alternating with glacier retreat and flotation over a marine water column. A combination of fjord basin sediment filling and sea-level oscillations may also have influenced the pattern of glacier ice advance and retreat within Beardmore Paleofjord. The marine Cloudmaker Formation is overlain by the terrestrial diamicton dominated Meyer Desert Formation. At Oliver Bluffs, the Meyer Desert Formation diamictons are interbedded with fluvial, and lacustrine sediments; successions that contain in situ vascular plant fossils (principally the Southern Beech Nothofagus), mosses, and beetle remains. A Magellanic-type flora and fauna occupied the coastal margins of the Beardmore Paleofjord. The vertical transition from the basal marine Cloudmaker Formation to terrestrial Meyer Desert Formation provides a sea-level datum that can be used to assess the extent of post-Sirius Group tectonic uplift. Uplift rates at the Cloudmaker section, 90 km inland from the Transantarctic Mountain front or rift shoulder margin in the Queen Alexandra Mountain block are determined to be ~ 429 or ~ 350 m/Myr. This assumes a total uplift of 1331 m for the uppermost marine sediments of the Cloudmaker Formation, and maximum diatom-based ages for the Sirius Group of < 3.1 Ma or < 3.8 Ma. Gross similarities in stratigraphy and interpreted paleoenvironments are apparent between The Cloudmaker succession (Beardmore Paleofjord) and the upper Miocene-Pliocene successions at the mouth of Taylor Paleofjord, 800 km to the north. Contrasting present day elevational settings for these two widely separated marine successions indicates the post-Sirius rate of tectonic uplift for the Transantarctic Mountains has been significantly greater in the Queen Alexandra block.     

Frost-weathering on Mars: Experimental evidence for peroxide formation

Summary A laboratory study of the interaction of H₂O frost with samples of the minerals olivine (Mg,Fe)₂SiO₄ and pyroxene (Mg,Fe)SiO₃ at –11°C to –22°C revealed that an acidic oxidant was produced. Exposure of the frost-treated minerals to liquid H₂O produced a sudden drop in pH and resulted in the production of copious O_2(g) (as much as ~ 10²⁰ molecules g^–1). Exposure of frost-treated samples to 5 ml of 0.1M HCOONa solution resulted in the rapid oxidation of up to 43% of the formate to CO_2(g). These reactions were qualitatively similar to the chemical activity observed during the active cycles of the Viking lander Gas Exchange and Labeled Release Biology experiments. Attempts to identify the oxidant by chemical indicators were inconclusive, but they tentatively suggested that chemisorbed hydrogen peroxide may have formed. The formation of chemisorbed peroxide could be explained as a byproduct of the chemical reduction of the mineral. The following model was proposed. H^c was incorporated into the mineral from surface frost. This would have left behind a residual of excess OH^– _(ads) (relative to surface H⁺). Electrons were then stripped from the surface OH^– _(ads) (due to the large repulsive potential between neighboring OH^– _(ads)) and incorporated into the crystal to restore charge balance and produce a chemical reduction of the mineral. The resultant surface hydroxyl radicals could then have combined to form the more stable chemisorbed hydrogen peroxide species. While the chemisorbed peroxide should be relatively stable at low temperatures, it should tend to decay to O_(ads) + H₂O_(g) at higher temperatures with an activation energy of 34 kcal mole^–1. This is consistent with the long-term storage and sterilization behavior of the Viking soil oxidants. It is possible that as little as 0.1–1% frost-weathered material in the Martian soil could have produced the unusual chemical activity that occurred during the Viking Gas Exchange and Labeled Release experiments.This paper contains the material given in invited presentations at the COSPAR Meeting, Innsbruck, Austria, 5–7 June 1978 and at the Second Conference on Simulation of Mars Surface Properties, NASA Ames Research Center, 17–18 August 1978     

Fatty acid biosynthesis by a particulate preparation from germinating pea

1. Fatty acid synthesis was studied in microsomal preparations from germinating pea (Pisum sativum). 2. The preparations synthesized a mixture of saturated fatty acids up to a chain length of C(24) from [(14)C]malonyl-CoA. 3. Whereas hexadecanoic acid was made de novo, octadecanoic acid and icosanoic acid were synthesized by elongation. 4. The products formed during [(14)C]malonyl-CoA incubation were analysed, and unesterified fatty acids and polar lipids were found to be major products. [(14)C]Palmitic acid represented a high percentage of the acyl-carrier protein esters, whereas (14)C-labelled very-long-chain fatty acids were mainly present as unesterified fatty acids. CoA esters were minor products. 5. The addition of exogenous lipids to the incubation system usually resulted in stimulation of [(14)C]malonyl-CoA incorporation into fatty acids. The greatest stimulation was obtained with dipalmitoyl phosphatidylcholine. Both exogenous palmitic acid and dipalmitoyl phosphatidylcholine increased the amount of [(14)C]-stearic acid synthesized, relative to [(14)C]palmitic acid. Addition of stearic acid increased the amount of [(14)C]icosanoic acid formed. 6. [(14)C]Stearic acid was elongated more effectively to icosanoic acid than [(14)C]stearoyl-CoA, and its conversion was not decreased by addition of unlabelled stearoyl-CoA. 7. Incorporation of [(14)C]malonyl-CoA into fatty acids was markedly decreased by iodoacetamide and 5,5'-dithiobis-(2-nitrobenzoic acid). Palmitate elongation was sensitive to arsenite addition, and stearate elongation to the presence of Triton X-100 or fluoride. The action of fluoride was not, apparently, due to chelation. 8. The microsomal preparations differed from soluble fractions from germinating pea in (a) synthesizing very-long-chain fatty acids, (b) not utilizing exogenous palmitate-acyl-carrier protein as a substrate for palmitate elongation and (c) having fatty acid synthesis stimulated by the addition of certain complex lipids.     

Lipid metabolism in green leaves of developing monocotyledons

Lipid synthesis was studied in successive leaf sections from the base to the tip of developing barley (Hordeum vulgare L.), maize (Zea mays L.), rye grass (Lolium perenne L.) and wheat (Triticum aestivum L.) leaves. The endogenous levels of acyl lipids and their constituent fatty acids from the same leaf sections were also analysed. The principle chloroplast acyl lipids showed a relative increase in amount with the age of the leaf section. Their content of -linolenic acid also increased whereas there was little change in the amount of this acid in phosphatidylcholine and phosphatidylethanolamine, which are primarily non-chloroplastic. The content of trans-3-hexadecenoic acid in phosphatidylglycerol increased approximately 20-fold between the youngest (basal) and oldest (distal) leaf sections.The incorporation of [¹⁴C]acetate was always high into monogalactosyldiacylglycerol, phosphatidylcholine and the neutral lipid (mainly pigments) fractions. With increasing age, the neutral lipids were less well labelled. In three of the plant species but not in barley, phosphatidylglycerol was heavily labelled. Monogalactosyldiacylglycerol usually contained the highest amount of radioactivity in the middle leaf sections. Apart from these generalisations, each plant type had its own specific pattern of radiolabelling.     

Direct identification and quantification of the cofactor in glutamate semialdehyde aminotransferase from pea leaves

Glutamate semialdehyde aminotransferase, a key enzyme in the synthetic pathway leading to chlorophyll was purified from pea (Pisum sativum) leaves. Although the preparation contained a single contaminant the enzyme could be unambiguously identified as a dimer of subunit molar mass 45 kDa having an absorption spectrum consistent with the presence of pyridoxamine phosphate as cofactor. The cofactor was released by treatment with strong phosphate at low pH and was identified and quantified fluorimetrically. The specific activity of the enzyme (1.4 mumol.min-1.mg-1; 23 nkatal.mg-1) is very much higher than previously reported.