EFFECT OF TREE CANOPY REMOVAL BY GYPSY MOTH LARVAE ON THE MACROALGAE OF A RHODE ISLAND HEADWATER STREAM1

A spring-fed, headwater stream in central Rhode Island was examined during the period from June to October, 1979 to 1982. In the first two summers, a dense riparian canopy reduced the light penetration at the stream surface to a range of 5 to 18% of incident radiation. The lotic macroalgal community during this period was limited to 1 to 4 species covering < 1 to 35% of the stream bottom. However, in June and July, 1981, the surrounding leaf canopy was removed by a massive gypsy moth larval outbreak. Light penetration to the stream during this summer increased to 73% by early July, thereby resulting in a rise in water temperatures by 3.7°C. Even though there was a partial regrowth of leaves in late July and August of 1981, macroalgal cover values continued to rise to an early August peak of 80%. During the third summer, 88% of the macroalgal abundance could be attributed to illumination and water temperature. The filamentous diatom Funotia pectinalis ( O.F. Müll.) Rabh. was the predominant species in the midsummer of all four years, accounting for at least 60% of the total cover. In 1981. an important taxon was the desmid Hyalotheca dissiliens (S. Smith) Bréb., a species which was not seen in other years. A less severe gypsy moth defoliation occurred in 1982 but did not produce significant differences in light, temperature or macroalgal cover from 1979 and 1980. The results indicate that light and temperature can be limiting during the summer in spring-fed, headwater streams and that seed populations of some species are present in undetect-able levels during these periods of suboptimal growth conditions. In addition, it appears that stream macroalgal communities can be quite resilient, recovering rapidly following a major perturbation .     

Large complex globular domains of type VII procollagen contribute to the structure of anchoring fibrils

Type VII collagen, in the form of an antiparallel dimer, is a major protein component of anchoring fibrils. The ultrastructural appearance of these fibrils suggests that they may serve to anchor the basement membrane zone to the underlying connective tissue matrix. We report here the identification and initial characterization of Type VII procollagen, recovered from the media of epidermoid carcinoma cell cultures. Immunoblotting using monospecific antibodies to Type VII procollagen identifies a single, homogeneous band of at least Mr 320,000 following disulfide bond reduction. This chain contains 170 kDa of collagen triple helix and 150 kDa of non-helical domain at the carboxyl terminus. Pepsin digestion of this material yields Type VII collagen identical to that isolated from whole tissue and a series of quasi-stable peptides derived from the carboxyl-terminal region. Cell extracts contain procollagen chains identical in size to those secreted into the media. There is no evidence for processing of this material in cell culture. Partial purification by velocity sedimentation and transmission electron microscopic observation following rotary shadowing reveals both monomers (426 nm) and dimers (785 nm). Dimers are antiparallel and interact through 60-nm overlap, with amino-terminal globular domains present at the ends of the overlap. The multi-domain carboxyl-terminal region appears as three similar arms originating from a centralized globular region adjacent to the collagen helix. The carboxyl globular domain is present in whole tissue and may participate in the unique fibril form of this collagen. The amino-terminal globule may function in the antiparallel assembly of dimers.     

THE OCCURRENCE OF PHYTOSEIULUS PERSIMILIS ATHIAS-HENRIOT (ACARINA:PHYTOSEIIDAE) IN AN ORCHARD IN VICTORIA

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High numbers of the predatory mite, Phytoseiulus persimilis , were found on apple and nectarine trees in a commercial orchard at Werribee, Victoria in February 1981. In the following season, again it was not detected on trees or broad-leaved weeds in the orchard until late summer. Slide-dip tests on the Werribee population of P. persimilis and a population originating from strawberries in Sydney, New South Wales, showed that azinphos-methyl was equally toxic to the 2 strains and DDT was considerably less toxic to both.     

Lactate extraction during net lactate release in legs of humans during exercise

Lactate metabolism was studied in six normal males using a primed continuous infusion of lactate tracer during continuous graded supine cycle ergometer exercise. Subjects exercised at 49, 98, 147, and 196 W for 6 min at each work load. Blood was sampled from the brachial artery, the iliac vein, and the brachial vein. Arteriovenous differences were determined for chemical lactate concentration and L-[1-14C]-lactate. Tracer-measured lactate extraction was determined from the decrease in lactate radioactivity per volume of blood perfusing the tissue bed. Net lactate release was determined from the change in lactate concentration across the tissue bed. Total lactate release was taken as the sum of tracer-measured lactate extraction and net (chemical) release. At rest the arms and legs showed tracer-measured lactate extraction, as determined from the isotope extraction, despite net chemical release. Exercise elicited an increase in both net lactate release and tracer-measured lactate extraction by the legs. For the legs the total lactate release (net lactate release + tracer-measured lactate extraction) was roughly equal to twice the net lactate release under all conditions. The tracer-measured lactate extraction by the exercising legs was positively correlated to arterial lactate concentration (r = 0.81, P less than 0.001) at the lower two power outputs. The arms showed net lactate extraction during exercise, which was correlated to the arterial concentration (r = 0.86). The results demonstrate that exercising skeletal muscle extracts a significant amount of lactate during net lactate release and that the working skeletal muscle appears to be a major site of blood lactate removal during exercise.     

The use of cobalt ions as a collisional quencher to probe surface charge and stability of fluorescently labeled bilayer vesicles

Co2+ quenched the fluorescence of the lipid probes NBD-phosphatidylethanolamine (NBD-PE) and lissamine-rhodamine phosphatidylethanolamine (N-Rh-PE) incorporated into lipid vesicles, according to a collisional quenching mechanism in agreement with the Stern-Vollmer law. The quenching coefficient (Q) for NBD-PE, incorporated into uncharged phosphatidylcholine (PC) vesicles was 13.8 M-1. This value was equal to the quenching coefficient of water-soluble NBD-taurine in aqueous solution, indicating that Co2+ was readily accessible to the outer surface of PC vesicles. In phosphatidylserine-phosphatidylethanolamine (PS-PE) (1:1) vesicles, quenching was also proportional to Co2+ concentration but Q was 114 mM-1, some 8000-fold smaller. Using the Gouy-Chapman-Stern model we demonstrated that the surface density of Co2+ bound to lipid was linear with Co2+ concentration in the medium up to 7%. Co2+-associated phospholipid would in turn quench NBD-PE or N-Rh-PE by collisional quenching with lateral diffusion. We investigated the ability of Co2+ to permeate PS-PE (1:1) vesicles. Co2+ quenched fluorophores on the outer surface of large unilamellar vesicles, formed by reverse-phase evaporation. In small unilamellar vesicles Co2+ quenched probes on both outer and inner surfaces, indicating rapid permeation of the ions into the vesicles. Using stopped-flow rapid mixing, we measured the rate of influx of Co2+, and correcting for surface potential using the Gouy-Chapman-Stern model, we calculated a permeability coefficient of 10(-12) cm/s for Co2+ concentrations below 300 microM. Above this concentration, there was a very steep rise in the permeability coefficient, indicating that binding of Co2+ induces defects in the bilayer of these vesicles. This may be related to the ability of the vesicles to undergo membrane fusion. A method for calculating the membrane surface potential from Co2+ quenching data is presented.     

Identification and functional analysis of beta-tubulin genes by site specific integrative transformation in Aspergillus nidulans

We have cloned two different beta-tubulin sequences from the filamentous fungus Aspergillus nidulans. Each was used in the construction of transforming plasmids that carry the pyr4 gene of Neurospora crassa. We used these plasmids to transform a pyrG-strain of Aspergillus to uridine prototrophy. Both plasmids were shown to integrate site specifically into the homologous chromosomal sequences. We then used transformant strains in genetic crosses to demonstrate that one of the cloned beta-tubulin sequences was the benA beta-tubulin gene, which codes for the beta 1-and beta 2-tubulins. The other cloned beta-tubulin sequence was shown to be the structural gene for beta 3-tubulin by gene disruption and to participate in conidial development. This is the first report of a gene disruption by site specific, integrative recombination in Aspergillus nidulans.     

Crystallization of a Fe,Zn superoxide dismutase from the archaebacterium Thermoplasma acidophilium

The novel Fe,Zn superoxide dismutase from the archaebacterium Thermoplasma acidophilium has been crystallized in space groups P1, P2(1) and P2(1)2(1)2, with 2,4 and 1/2 of an 84,000 Mr tetramer, respectively, estimated to be in the asymmetric unit of the unit cell. The orthorhombic crystals, which have unit cell dimensions a = 84.2 A, b = 72.7 A, c = 67.8 A, diffract X-rays to at least 2.0 A and are suitable for a determination of the three-dimensional structure of the Fe,Zn superoxide dismutase.     

Dietary chloride as a determinant of disordered calcium metabolism in salt-dependent hypertension

In rats given desoxycorticosterone (DOC), the recently reported finding that a normal amount of dietary sodium chloride (NaCl) induces hypertension but an equimolar amount of sodium bicarbonate (NaHCO3) does not, might be a consequence of the differing effects of the two sodium salts on the metabolism of calcium. In accord with this hypothesis, we have found that, in uninephrectomized rats given DOC: Dietary NaCl induces persisting hypercalciuria and hypertension whereas an approximately equimolar amount of dietary NaHCO3 induces neither hypercalciuria nor hypertension. The urinary excretion of calcium becomes greater in rats given NaCl than in those given NaHCO3, before their blood pressures become different. Replacing dietary NaCl with a near equimolar amount of dietary NaHCO3 corrects both the hypercalciuria and the hypertension initially induced by NaCl.     

Varying Photoperiod, Ribulose 1,5-Bisphosphate Carboxylase/Oxygenase and CO(2) Uptake in Thalassiosira fluviatilis (Bacillariophyceae)

The purpose of this research was to test the hypothesis that acclimation of the unicellular marine alga, Thalassiosira fluviatilis Hustedt, to short photoperiods results in decreased cellular concentrations of ribulose 1,5-bisphosphate carboxylase/oxygenase and decreased rates of light-saturated CO₂ uptake. Cells were acclimated to photoperiods of 6:18, 12:12, and 18:6 h:h light:dark, and concentrations of the large subunit of the enzyme and responses of CO₂ uptake to varying irradiance were measured. Concentrations of the large subunit, which weighed approximately 50 kilodaltons, were conserved while rates of CO₂ uptake under light saturation and limitation, and cellular contents of chlorophyll a increased as photoperiod decreased. Apparently, these cells acclimate to short photoperiods by increasing rates of CO₂ uptake under saturating irradiances by increasing in vivo activation of ribulose 1,5-bisphosphate carboxylase/oxygenase. Also, chlorophyll-specific concentrations and specific activities of the enzyme appear to be lower and higher, respectively, in diatomaceous algae than in higher plants.     

A preliminary study of aquatic insect communities and leaf decomposition in acid streams near Dorset,Ontario

Some streams near Dorset in south-central Ontario suffer from acid precipitation via run-off and seepage from thin soils with little buffering capacity. A spring-summer survey of eight headwater streams revealed some characteristics of their insect communities which could be correlated with pH. The streams could be divided into three groups according to pH and community structure. In the most acid group (annual pH range 4.3–4.8), Ephemeroptera were absent from two streams although mature Leptophlebia were collected just after spring thaw from the most acid one (pH 4.3–4.5). One of these three streams also lacked Plecoptera but the others had two or three genera, all shredders. The second group of three streams (pH 5.0–6.3), with one exception, did support Ephemeroptera (3–4 genera) and Plecoptera (1–4 genera), most of the latter being shredders. In all six of these acid streams, Trichoptera were more diverse and more dense than Ephemeroptera and Plecoptera; again, shredders were clearly dominant, especially the limnephilid caddisfly, Frenesia difficilis (Walker). These six streams also had similar chironomid communities (densities were an order of magnitude higher than other insects). Dominance by Chironomini and abundant Tanypodinae typified the most acid streams. In contrast, the two streams in the third group (pH 5.3–6.7) had richer and more balanced communities in general with relatively fewer shredders (no Frenesia), more collectors, and fewer Chironomini and Tanypodinae. As a field experiment showed that autumn-shed leaves decomposed more slowly in acid than in non-acid streams, summer-growing shredders may benefit from the pulse of acidity at snowmelt.