Force-length relations of glycerinated rabbit psoas.

Force-length curves of glycerinated rabbit psoas were determined in media of physiological interest. In one set of experiments the free [Ca++] was constant at 10(-5) M and the [MgATP] varied. At low [MgATP] the elastic properties are those of a highly ordered, inextensible fiber; at high [MgATP] they are representative of a much more elastic body. At intermediate concentrations sigmoidal shaped curves were observed as were also found when [MgATP] was constant and the free [Ca++] varied. These curves closely resemble coexistence curves that have been reported for fibrous proteins.     

Structure and stability of the P93G variant of ribonuclease A.

The peptide bonds preceding Pro 93 and Pro 114 of bovine pancreatic ribonuclease A (RNase A) are in the cis conformation. The trans-to-cis isomerization of these bonds had been indicted as the slow step during protein folding. Here, site-directed mutagenesis was used to replace Pro 93 or Pro 114 with a glycine residue, and the crystalline structure of the P93G variant was determined by X-ray diffraction analysis to a resolution of 1.7 A. This structure is essentially identical to that of the wild-type protein, except for the 91-94 beta-turn containing the substitution. In the wild-type protein, the beta-turn is of type VIa. In the P93G variant, this turn is of type II with the peptide bond preceding Gly 93 being trans. The thermal stabilities of the P93G and P114G variants were assessed by differential scanning calorimetry and thermal denaturation experiments monitored by ultraviolet spectroscopy. The value of delta deltaGm which reports on the stability lost in the variants, is 1.5-fold greater for the P114G variant than for the P93G variant. The greater stability of the P93G variant is likely due to the relatively facile accommodation of residues 91-94 in a type II turn, which has a preference for a glycine residue in its i + 2 position.     

Pyramimonas amylifera Conrad (Prasinophyceae): seasonal dynamics of a wild population, and the effects of temperature and salinity on growth and survival in culture

Temperature, salinity and abundance of Pyramimonas amyliferawere monitored over a 1-year period in a tidal salt marsh pool.The organism reached two peaks of abundance, the first in latefall before ice covered the pool, and the second in late winterafter the ice had melted. Cysts, but no oc-toflagellate stagesof this organism, were found in the pool in summer. The resultsof growth experiments on a clone of this organism isolated fromthe pool indicate that a temperature between 10 and 15 C isoptimal. A temperature between 20 and 25 C is the maximum tolerableby this clone. The "short-term" salinity tolerance range ofthis clone was found to decrease with increasing temperature,a phenomenon which could affect the fitness of the organismas a tide pool inhabitant. The field and laboratory data indicatethat although temperature and salinity were factors affectingthe abundance of P. amylifera in the pool, other factors notconsidered in the study must have also been important. ^*Present address: Department of Biology, University of SouthFlorida, Tampa, Florida, U.S.A. 33620. (Address for reprints)     

Effect of selected marine and freshwater microalgae on development and survival of the mosquito <Emphasis Type="Italic">Aedes aegypti</Emphasis>

We isolated and identified strains of marine and freshwater planktonic and benthic microalgae from the vicinity of Indian River County, Florida (≈27.5°N, 80.34°W), cultivated them in batch culture, and examined their allelopathic activity against mosquito larvae. Additional algal material was obtained from Syracuse University and the University of Texas—Austin Algal Culture Collection. Mosquito larvae (Aedes aegypti (L.)) from colonies maintained at the Florida Medical Entomology Laboratory were challenged with the microalgae using log-growth phase and senescent-phase cultures. Appropriate controls (no algae) were used for each treatment. There were no significant differences in development time between treatments across all trials and a few significant treatment effects on development times, mortality, or mosquito size in the individual trials; however, there was a tendency for treatments with senescent microalgae to develop faster than controls with no algae. Effects consistent with algal toxicity included the two trials with Microcystis aeruginosa, where the larvae exposed to the strain-producing microcystin had significantly longer development times than the controls or those grown with the non-microcystin-producing strain, and the trial with the dinoflagellate Akashiwo sanguinea, where larvae exposed to this species had significantly higher mortality than the controls. No consistent patterns or differences between experimental and control treatments in the value of λ′, an estimate of the population finite rate of increase, were discernible from the data.     

DESCRIPTION AND CHARACTERIZATION OF THE ALGAL SPECIES AUREOUMBRA LAGUNENSIS GEN. ET SP. NOV. AND REFERRAL OF AUREOUMBRA AND AUREOCOCCUS TO THE PELAGOPHYCEAE1

The Texas brown tide alga (strain TBA-2) is described as Aureoumbra lagunensis Stockwell, DeYoe, Hargraves, et Johnson, gen. et sp. nov. Pigment composition, chloroplast structure, and 18s ribosomal RNA gene sequence data indicate that A. lagunensis and the east coast brown tide alga Aureococcus anophagefferens (originally placed in the Chrysophyceae) belong in the class Pelagophyceae. The new genus Aureoumbra with A. lagunensis as the type species differs from Aureococcus in 18s ribosomal RNA gene sequence, pyrenoid form, nitrogen physiology, and possession of basal bodies. The genus Aureococcus is placed in the order Pelagomonadates and family Pelagomonadaceae while ordinal placement of Aureoumbra is deferred.     

SPORE FORMATION IN THE LIFE CYCLES OF THE DIATOMS CHAETOCEROS DIADEMA AND LEPTOCYLINDRUS DANICUS1

A nitrogen limitation technique elicited the entire life cycle of the marine centric diatoms Chaetoceros diadema (Ehr.) Gran and Leptocylindrus danicus Cleve. In C. diadema the sexual cycle followed the same pattern as in the previously investigated C. didymus. Sexuality took place in narrow diameter cells, only at 2 and 5° C, and was seldom seen. Resting spore formation took place in cells of all sizes and at all temperatures at which the species grew vegetatively (2–15° C). The L. danicus life cycle is probably unique among diatoms. Nitrogen depletion induced sexuality in the entire culture at 10 and 15° C if the cell diameter was narrow (3–8 μm). Auxospore formation was followed by resting spore formation directly within the auxospore. In C. diadema, as in most centric diatoms, resting spores are not an obligate part of the life cycle, but they are in L. danicus. Resting spore formation is a versatile adaptive response in C. diadema, depending only on nitrogen depletion, although promoted by low temperatures. In L. danicus the linkage to the sexual process sharply limits conditions under which resting spores can form.     

STUDIES ON MARINE PLANKTON DIATOMS. III. STRUCTURE AND CLASSIFICATION OF GOSSLERIELLA TROPICA1

The structure of the tropical oceanic diatom Gossleriella tropica Schütt was examined in the light and electron microscopes. The species is characterized by a primarily poroid valve, surface, it single central labiate process and a unique ring of spines attached to the cingulum. Placement of the genus in the family Rhizosoleniaceae is suggested. Although G. tropica is widely distributed in the world's oceans, it is usually confined to the lower photic zone, salinities of 34.5–35.5% and temperatures of 15–30 C.     

Pulmonary Changes in Lung Purpura and Some of the Other Collagen Diseases

The physician who specializes in pulmonary diseases has a most helpful aid in the form of chest roentgenography. This examination is secured routinely in many hospitals and clinics today. The roentgenogram is very accurate in finding pulmonary lesions. Accuracy in determining the type of lesion depends on the experience of the physician who is studying the patient.Pulmonary lesions occur in many systemic diseases. They may occur in some of the collagen diseases and at times they may be the first and also the most striking findings noted during the examination of a patient. For this reason, attention is called to some of the pulmonary findings encountered in certain of these diseases. Some of the clinical, roentgenologic and pathologic manifestations of necrotizing alveolitis, periarteritis nodosa, glomerulonephritis, disseminated lupus erythematosus, rheumatoid arthritis, and scleroderma are described.     

Comparative benthic plant ecology by SCUBA-monitored quadrats

The feasibility of permanent benthic quadrats checked by SCUBA divers was tested. Stations were set up on the bottom of six representative aquatic habitats, both marine and inland, including oligotrophic and eutrophic ponds, river, coastal lagoon, estuary, and open marine coast. Data include physical-chemical factors, species composition, number and height of shoots, and general observations. From volume/length constants, the standing crops per quadrat were calculated. Seasonal changes in environmental factors and plant standing crop are parallel-plotted for the six habitats, thus providing comparative information on stations. Benthic diel periodicity and light intensity periodicity at various depths were investigated also. In all habitats, maximum standing crop occurred in July and August, but species composition varied considerably. Length of time the water temperature exceeded 15C did not correlate with standing crop. Dissolved oxygen was never deficient, even under ice; and diurnal changes were slight. Light was diminished under ice, but 4–60 ft-c were recorded in midwinter. Lenght of day is about 2 hours shorter at 20 ft than at 6 ft. Onset of vernal benthic growth seems correlated more closely with increase in light intensity than with temperature. The permanent quadrats monitored by divers proved feasible in all habitats tested, and directly comparable data were obtained.Supported in part by a grant from the National Science Foundation.     

The life history of Pyramimonas amylifera Conrad (Prasinophyceae)

Several possible life history stages of a clone of Pyramimonasamylifera Conrad (Prasinophyceae) have been encountered in culturestudies. These include: 1) octoflagellates; 2) cysts; 3) quadriflagellates;4) biflagellates; and 5) multilobate cells with each lobe bearingeight flagella. The octoflagellates have the ultra-structuralcharacteristics previously documented for P. amylifera. Scanningelectron microscopy was used to examine surfaces of cysts andbiflagellates. Scales of the type which form the middle (basket-shaped)and outer (coronate) scale layers on the octoflagellate wereobserved on the surface of cysts. Scales of the type which formthe middle body layer on octoflagellates were observed on thebodies of biflagellates. Biflagellates, quadriflagellates, andempty cysts were observed in several cultures which had beensubjected to a 5-week dark incubation before return to a low-lightregime. In one of those cultures, a single cyst containing motileswarmers was observed. The biflagellates or quadriflagellatesmay represent cyst-germination products. ^*Present address: Department of Biology, University of SouthFlorida, Tampa, Florida, U.S.A. 33620.