Metabolic cost of motility in planktonic protists: Theoretical considerations on size scaling and swimming speed

The metabolic cost of swimming for planktonic protists is calculated, on theoretical grounds, from a simple model based upon Stokes' law. Energetic expenditure is scaled over both typically encountered size ranges (1–100 µm) and swimming speeds (100–5,000 µm/sec). In agreement with previous estimates for typical flagellates, these estimates generally suggest a low (<1%) cost for motility, related to total metabolic rate of growing cells. However, the cost of motility in small, fast-moving forms, such as some ciliates and flagellates, may be significant (1–10%) and even substantial (10–100%+) for certain species. In accordance with these predictions, many fast-moving ciliates restrict motility to bursts of activity or jumps. In the absence of a reduction in swimming speed or in the frequency of jumps, it is predicted that this relative cost of motility will be significantly increased in starving heterotrophs or light-limited autotrophs, if such cells reduce cell volumes and specific rates of respiration.     

Wall shear stress estimates in coronary artery constrictions.

Wall shear stress estimates from laminar boundary layer theory were found to agree fairly well with the magnitude of shear stress levels along coronary artery constrictions obtained from solutions of the Navier Stokes equations for both steady and pulsatile flow. The relatively simple method can be used for in vivo estimates of wall shear stress in constrictions by using a vessel shape function determined from a coronary angiogram, along with a knowledge of the flow rate.     

Identification and reconstitution of the nucleoside transporter of CEM human leukemia cells

The major nucleoside transporter of the human T leukemia cell line CEM has been identified by photoaffinity labeling with the transport inhibitor nitrobenzylmercaptopurine riboside (NBMPR). The photolabeled protein migrates on SDS-PAGE gels as a broad band with a mean apparent molecular weight (75,000 +/- 3000) significantly higher than that reported for the nucleoside transporter in human erythrocytes (55,000) (Young et al. (1983) J. Biol. Chem. 258, 2202-2208). However, after treatment with endoglycosidase F to remove carbohydrate, the NBMPR-binding protein in CEM cells migrates as a sharp peak with an apparent molecular weight (47,000 +/- 3000) identical to that reported for the deglycosylated protein in human erythrocytes (Kwong et al. (1986) Biochem. J. 240, 349-356). It therefore appears that the difference in the apparent molecular weight of the NBMPR-sensitive nucleoside transporter between the CEM cell line and human erythrocytes is a result of differences in glycosylation. The NBMPR-binding protein from CEM cells has been solubilized with 1% octyl glucoside and reconstituted into phospholipid vesicles by a freeze-thaw sonication technique. Optimal reconstitution of uridine transport activity was achieved using a sonication interval of 5 to 10 s and lipid to protein ratios of 60:1 or greater. Under these conditions transport activity in the reconstituted vesicles was proportional to the protein concentration and was inhibited by NBMPR. Omission of lipid or protein, or substitution of a protein extract prepared from a nucleoside transport deficient mutant of the CEM cell line resulted in vesicles with no uridine transport activity. The initial rate of uridine transport, in the vesicles prepared with CEM protein, was saturable with a Km of 103 +/- 11 microM and was inhibited by adenosine, thymidine and cytidine. The Km for uridine and the potency of the other nucleosides as inhibitors of uridine transport (adenosine greater than thymidine greater than cytidine) were similar to intact cells. Thus, although the nucleoside transporter of CEM cells has a higher molecular weight than the human erythrocyte transporter, it exhibits typical NBMPR-sensitive nucleoside transport activity both in the intact cell and when reconstituted into phospholipid vesicles.     

CHLOROPLAST DNA RESTRICTION SITE VARIATION AND THE PHYLOGENY OF COREOPSIS SECTION COREOPSIS (ASTERACEAE)

Restriction site variation in chloroplast DNAs (cpDNAs) of Coreopsis section Coreopsis was employed to assess divergence and phylogenetic relationships among the nine species of the section. A total of fourteen restriction site mutations and one length mutation was detected. Cladistic analysis of the cpDNA data produced a phylogeny that is different in several respects from previous hypotheses. CpDNA mutations divide the section into two groups, with the two perennial species C. auriculata and C. pubescens lacking any derived restriction site changes. The other seven species are united by five synapomorphic restriction site mutations and the one length mutation. These seven species fall into three unresolved clades consisting of 1) the remaining three perennial species, C. grandiflora, C. intermedia, and C. lanceolata; 2) three annual species, C. basalis, C. nuecensoides, and C. nuecensis; and 3) the remaining annual, C. wrightii. The cpDNA data suggest that, although the perennial habit is primitive within the section, the annual species of section Coreopsis have likely not originated from an extant perennial species. The estimated proportion of nucleotide differences per site (given as 100p) for the cpDNAs of species in the section ranges from 0.00 to 0.20, which is comparable to or lower than values reported for other congeneric species. The low level of cpDNA divergence is concordant with other data, including cross compatibility, interfertility and allozymes, in suggesting that species of the section are not highly divergent genetically.     

PHYLOGENETIC IMPLICATIONS OF DIFFERENCES IN NUMBER OF PLASTID PHOSPHOGLUCOSE ISOMERASE ISOZYMES IN NORTH AMERICAN COREOPSIS (ASTERACEAE: HELIANTHEAE: COREOPSIDINAE)

Enzyme electrophoresis was employed to ascertain the number of loci encoding plastid phosphoglucose isomerase (PGI) in species representing all sections of North American Coreopsis. Several species from each of the closely related genera Bidens, Coreocarpus, Cosmos, and Thelesperma were also examined. Species in nine of the 11 sections of North American Coreopsis have two isozymes for plastid PGI, and nearly all species examined in the four other genera also have two (one species has three) isozymes. Since most diploid vascular plants have one plastid PGI isozyme, a gene duplication probably occurred in an ancestor that is common to Coreopsis and the other four genera. That is, two isozymes represent the ancestral number for Coreopsis. The two sections (Electra and Anathysana) apparently lacking the duplication are closely related woody plants restricted largely to Mexico. One gene encoding plastid PGI ostensibly was silenced in a common ancestor of these two sections. This is concordant with other data suggesting a close relationship between the two sections, i.e., they appear to represent a monophyletic group. The electrophoretic data also indicate that 1) the enigmatic monotypic section Silphidium is more closely related to eastern North American sections and not derived from section Electra; and 2) section Anathysana is not ancestral to the three California sections Leptosyne, Pugiopappus, and Tuckermannia; rather, it represents a terminal element closely related to and possibly derived from section Electra.     

Radioimmunoassay of the cellular protein p53 in mouse and human cell lines

We have developed quantitative radioimmunological solid phase assays for the host protein p53 from mouse cells and from human cells. The first assay, for mouse p53, depends on having two monoclonal antibodies reacting with different determinants on the p53 molecule. With this assay we have shown that SV40-transformed cells have approximately 100-fold more p53 than untransformed mouse cells and that other transformed cells have intermediate levels. Embryonal carcinoma cell lines have approximately 50-fold less p53 than SV40-transformed cells. This is in contrast to the high levels of incorporation of [35S]methionine into p53 in these cells and indicates that metabolic labelling is not a valid approach for measuring p53 levels. The second assay, for human p53, required a different approach and made use of the anti-p53 antibodies detected in the sera of some breast cancer patients. Human tumour cell lines contained amounts of p53 varying from the high level seen in SV40-transformed human fibroblasts down to less than one hundredth of this amount. Normal human cells showed low levels of p53. The data confirm that many, but not all, human tumour cell lines contain more p53 than normal cells.     

Degradation of extractive-free lignocelluloses by Coriolus versicolor and Poria placenta

Summary The wood-decay fungi Coriolus versicolor, a white-rot fungus, and Poria placenta, a brown-rot fungus, were grown on an extractive-free lignocellulose prepared from quackgrass (Agropyron repens). Their abilities to decompose this lignocellulose were compared to their abilities to decompose softwood (Picea pungens) and hardwood (Acer rubrum) lignocelluloses. The two fungi were grown on malt-extract dampened lignocelluloses at 28°C for up to 12 weeks. Replicate cultures were periodically harvested and lignocellulose decomposition was followed by monitoring substrate weight loss, lignin loss, and carbohydrate loss. Coriolus versicolor decomposed the lignin and carbohydrate components of the grass lignocellulose as efficiently as the softwood and hardwood lignocelluloses. Poria placenta, however, was not an efficient degrader of either lignin or carbohydrate in the grass lignocellulose. Poria placenta readily decomposed carbohydrate components of the softwood lignocellulose but not the hardwood lignocellulose.Paper number 81520 of the Idaho Agricultural Experiment Station     

Adenylate cyclase of human articular chondrocytes. Responsiveness to prostaglandins and other hormones.

Adenylate cyclase [ATP pyrophosphate lyase (cyclizing), EC 4.6.1.1] was shown to be present in cultured human articular chondrocytes. Optimal conditions of incubation time, protein and substrate concentrations and pH were determined in whole cell lysates. Maximal activity occurred at pH 8.5 with no decrease in activity up to pH 10.0. Adenylate cyclase activity of particulate membrane preparations was enhanced by the addition of crude cytosol preparations. The prostaglandins E1, E2, F1 alpha, F2 alpha, D2, B1, B2, A1 and A2, as well as adrenaline and isoprenaline, stimulated adenylate cyclase derived from either adult or foetal chondrocytes. No significant stimulation was observed in the presence of human calcitonin or glucagon. Bovine parathyroid hormone always significantly stimulated the adenylate cyclase derived from foetal chondrocytes, but not from adult chondrocytes. Preincubation of the chondrocytes in culture with indomethacin and with or without supernatant medium from cultured mononuclear cells increased the responsiveness of the adenylate cyclase to prostaglandin E1.     

The cytokineplast: purified, stable, and functional motile machinery from human blood polymorphonuclear leukocytes

We examined the formation of motile, chemotactically active, anucleate fragments from human blood polymorphonuclear leukocytes (PMN, granulocytes), induced by the brief application of heat. These granule-poor fragments are former protopods (leading fronts, lamellipodia) that become uncoupled from the main body of the cell and leave it, at first with a connecting filament that breaks and seals itself. The usual random orientation of such filaments can be controlled by preorientation of cells in a gradient of the chemotactic peptide, N-formylmethionylleucylphenylalanine (F-Met-Leu-Phe) (2x10(-9) M- 1x10(-8)). Cytochalsin B, 2.5-5 μg/ml, prevents fragment formation; colchicine, 10(-5) M, does not. In scanning electron micrographs, fragments are ruffled and the cell body rounded up and rather smooth. In transmission electron micrographs, fragments contain microfilaments but lack centrioles and microtubules. Like intact cells, both bound and free fragments can respond chemotactically to an erythrocyte destroyed by laser microirradiation (necrotaxis); the free, anucleate fragments may do so repeatedly, even after having been held overnight at ambient temperatures. We propse the name cytokineplast for the result of this self-purification of motile apparatus. The exodus of the motile machinery from the granulocyte requires anchoring of the bulk of the cell to glass and uncoupling, which may involve heat-induced dysfunction of the centrosome. In ultrastructural studies of the centrosomal region after heat, centriolar structure remains intact, but pericentriolar osmiophilic material appears condensed, and microtubules are sparse. These changes are found in all three blood cell types examined: PMN, eosinophil, and monocyte. Of these, the first two make fragments under our conditions; the more sluggish monocyte does not. Uncoupling is further linked to centrosomal dysfunction by the observation that colchicines-treated granulocytes (10(-5)M, to destroy the centrosome’s efferent arm) make fragments after less heat than controls. If motive force and orientation are specified mainly from the organelle-excluding leading front, then endoplasmic streaming in PMN is a catch-up phenomenon, and microtubules do not provide the vector of locomotion but rather stabilize and orient the “baggage” (nucleus, granuloplasm)—i.e., they prevent fishtailing. Moreover, constraints emanating from the centrosome may now be extended to include, maintenance of the motile machinery as an integral part of the cell.     

Sources, Fluxes, and Sinks of Nitrogen during Early Reproductive Growth of Maize (Zea mays L.)

A study was designed to (a) identify sources and sinks of N in the maize (Zea mays L.) shoot, by estimating net N fluxes for each of seven parts of the shoot, (b) determine effects of N entering the plant upon fluxes of N absorbed before reproductive growth, and (c) determine the effects of the opaque-2 gene on N fluxes in the maize shoot during early reproductive growth. Plants of a maize hybrid (Pioneer 3369A) and its opaque-2 counterpart (Pioneer L3369) were grown in a greenhouse using nutrient solution/sand culture, with NO₃⁻ as the N source during the vegetative growth phase. Beginning at the time of pollination, the same nutrient regime was continued, except that some plants received no N, and others received 3.75 millimolar ¹⁵N as NO₃⁻-N.

Stalk and leaves were found to be primary N sources for the grain, while shank, husk, and cob acted first as N sinks, then as N sources during reproductive growth. Net fluxes of N for each plant part were estimated by calculating the first derivatives of regression equations used to fit data for N contents of each plant part as functions of time. All parts of the shoot were sinks for exogenous N (absorbed after pollination). Thirty-six days after pollination, the grain contained 60% endogenous N (absorbed before pollination) when 3.75 millimolar NO₃⁻-N was supplied after pollination. Rates of total N influx to the grain were identical whether or not N was supplied in the nutrient solution during reproductive growth. At 36 days after pollination, less N had accumulated in the grain of the opaque-2 genotype, but otherwise there were no differences in N contents or dry weights of the shoots due to the opaque-2 gene. Absence of N from the rooting medium significantly affected N fluxes throughout the shoot during reproductive growth, but there were no detectable effects of the opaque-2 gene on N fluxes in parts of the plant other than the grain.