Volatiles from the epicuticular wax of watercress (Rorippa nasturtium-aquaticum)

Volatiles from the epicuticular wax of watercress were collected by ether washing and examined using gas chromatographic and mass spectrometric analysi     

The mechanism of nitrogen monoxide (NO)-mediated iron mobilization from cells. NO intercepts iron before incorporation into ferritin and indirectly mobilizes iron from ferritin in a glutathione-dependent manner.

Nitrogen monoxide (NO) is a cytotoxic effector molecule produced by macrophages that results in Fe mobilization from tumour target cells which inhibits DNA synthesis and mitochondrial respiration. It is well known that NO has a high affinity for Fe, and we showed that NO-mediated Fe mobilization is markedly potentiated by glutathione (GSH) generated by the hexose monophosphate shunt [Watts, R.N. & Richardson, D.R. (2001) J. Biol. Chem. 276, 4724-4732]. We hypothesized that GSH completes the coordination shell of an NO[bond]Fe complex that is released from the cell. In this report we have extended our studies to further characterize the mechanism of NO-mediated Fe mobilization. Native PAGE 59Fe-autoradiography shows that NO decreased ferritin-59Fe levels in cells prelabelled with [59Fe]transferrin. In prelabelled cells, ferritin-59Fe levels increased 3.5-fold when cells were reincubated with control media between 30 and 240 min. In contrast, when cells were reincubated with NO, ferritin-59Fe levels decreased 10-fold compared with control cells after a 240-min reincubation. However, NO could not remove Fe from ferritin in cell lysates. Our data suggest that NO intercepts 59Fe on route to ferritin, and indirectly facilitates removal of 59Fe from the protein. Studies using the GSH-depleting agent, L-buthionine-(S,R)-sulphoximine, indicated that the reduction in ferritin-59Fe levels via NO was GSH-dependent. Competition experiments with NO and permeable chelators demonstrated that both bind a similar Fe pool. We suggest that NO requires cellular metabolism in order to effect Fe mobilization and this does not occur via passive diffusion down a concentration gradient. Based on our results, we propose a model of glucose-dependent NO-mediated Fe mobilization.     

Photosynthetic action spectra and adaptation to spectral light distribution in a benthic cyanobacterial mat

We studied adaptation to spectral light distribution in undisturbed benthic communities of cyanobacterial mats growing in hypersaline ponds at Guerrero Negro, Baja California, Mexico. Microscale measurements of oxygen photosynthesis and action spectra were performed with microelectrodes; spectral radiance was measured with fiber-optic microprobes. The spatial resolution of all measurements was 0.1 mm, and the spectral resolution was 10 to 15 nm. Light attenuation spectra showed absorption predominantly by chlorophyll a (Chl a) (430 and 670 nm), phycocyanin (620 nm), and carotenoids (440 to 500 nm). Blue light (450 nm) was attenuated 10-fold more strongly than red light (600 nm). The action spectra of the surface film of diatoms accordingly showed activity over the whole spectrum, with maxima for Chl a and carotenoids. The underlying dense Microcoleus population showed almost exclusively activity dependent upon light harvesting by phycobilins at 550 to 660 nm. Maximum activity was at 580 and 650 nm, indicating absorption by phycoerythrin and phycocyanin as well as by allophycocyanin. Very little Chl a-dependent activity could be detected in the cyanobacterial action spectrum, even with additional 600-nm light to excite photosystem II. The depth distribution of photosynthesis showed detectable activity down to a depth of 0.8 to 2.5 mm, where the downwelling radiant flux at 600 nm was reduced to 0.2 to 0.6% of the surface flux.     

Lysophosphatidylcholine as an intermediate in phosphatidylcholine metabolism and glycerophosphocholine synthesis in cultured cells: an evaluation of the roles of 1-acyl- and 2-acyl-lysophosphatidylcholine

Previous studies in our laboratory have shown that the principal pathway of phosphatidylcholine (PtdCho) degradation in cultured mouse N1E-115 neuroblastoma, C6 rat glioma, primary rat brain glia and human fibroblasts is PtdCho----lysophosphatidylcholine (lysoPtdCho)----glycerophosphocholine (GroPCho)----glycerophosphate plus choline (Morash, S.C. et al. (1988) Biochim. Biophys. Acta 961, 194-202). GroPCho is the first quantitatively major degradation product in this pathway, and could be formed by phospholipases A1 or A2, followed by lysophospholipase, or by a co-ordinated attack releasing both fatty acids by phospholipase B. The quality and quantities of lysoPtdCho present in cells reflect the nature of the initial hydrolysis step (A1 or A2), specificities of the lysophospholipases, and activities of acyltransferases that form PtdCho from lysoPtdCho. The present study was undertaken to elucidate the relative importance of these pathways by examining the fate of exogenous 1-acyl and 2-acyl-lysoPtdCho incubated with N1E-115 and C6 cells in culture. By fatty acid composition, endogenous lysoPtdCho was found to be mainly 1-acyl in both cell types based on a predominance of saturated acyl species; this suggested either preferential further deacylation or reacylation of 2-acyl-lysoPtdCho, or that 2-acyl-lysoPtdCho was not formed. Exogenous 1- and 2-acyl-lysoPtdCho specifically radiolabelled with choline and/or fatty acid were incubated either singly or as equimolar mixtures with cells. Cell association was rapid and not reversible by washing and both species were taken up at similar rates. The 2-acyl species was acylated to PtdCho faster than the 1-acyl species in both cell lines. Acylation of both lyso species was higher in C6 compared to N1E-115 cells. Hydrolysis of lysoPtdCho to GroPCho was higher in N1E-115 cells and with 1-acyl-lysoPtdCho. Transacylation between two molecules of lysoPtdCho was a minor pathway. These results document the variety and relative importance of reactions of lysoPtdCho metabolism; under similar conditions, 1- and 2-acyl-lysoPtdCho are handled differently. Both species turn over actively, but only the 1-acyl species accumulates while 2-acyl-lysoPtdCho is likely to be reacylated to form PtdCho.     

Blood flow changes following 137Cs irradiation in a rat glioma model

Blood flow changes in response to 20 Gy 137Cs whole brain irradiation were measured with quantitative autoradiography of [14C]iodoantipyrine (IAP) in intracerebral grafts of the 36B-10 rat glioma, the brain around tumor (BAT), the contralateral corpus callosum, and the contralateral cerebral cortex. Irradiations were delivered on Day 14 post-transplantation, and measurements of flow (F) were performed with IAP on Day 15 or Day 16. Mean values of F were determined in individual tumors and in treatment groups. In 15- and 16-day-old unirradiated control tumors, the group mean F was 0.31 ml.g-1.min-1. In both 15- and 16-day-old tumor groups irradiated on Day 14 (Day 1 and 2 postirradiation tumors) the mean F for each day's group was 0.52 ml.g-1.min-1, 68% higher than the control (P less than 0.01). Flow in the BAT and the contralateral corpus callosum similarly was increased at these times (P less than 0.01). Flow in the contralateral cerebral cortex was 1.1, 1.5, and 1.3 ml.g-1.min-1 in the control, 1 day postirradiated, and 2 day postirradiated groups, respectively, but these increases were not significantly different from the control. These data indicate that flow increases in the intracerebral gliomas as well as in normal brain regions during the 2 days following 20 Gy irradiation. Changes such as these following radiotherapy may have important effects on the bioavailability of chemotherapeutic drugs.     

Genetic localization of Hao-1, blind-sterile (bs), and Emv-13 on mouse chromosome 2.

The blind-sterile (bs) mutation in the mouse was localized on Chromosome 2 between Hao-1 and Emv-13. N2 progeny from a backcross between congenic female 129.AKR-bs Emv-13 mice and (129.AKR-bs/bs x Mus musculus molossinus) F1 male mice were typed by analysis of isozyme variants for Hao-1, visible inspection for bs, and restriction fragment length polymorphism for Emv-13 and Emv-15. Comparison between markers on mouse Chromosome 2 and corresponding markers on human chromosomes suggest that the human homolog of bs will be located on 20q11-q13.     

A molecular genetic approach to the identification of isochromosomes of chromosome 21

Summary The largest class of de novo chromosomal rearrangements in Down syndrome are rea(21q21q). Classically, these rearrangements have been termed Robertsonian translocations, implying an attachment of two different chromosome 21 homologues. Additionally, a Robertsonian translocation between two chromosomes 21 cannot be distinguished from an isochromosome composed of genetically identical arms by cytogenetic analyses. Therefore, we have used molecular techniques to differentiate between true Robertsonian translocations and isochromosomes. Samples were obtained from 12 probands, ascertained for de novo rearrangements between homologous chromosomes 21 [11 rea(21q21q) and 1 rea (21;21)(q22;q22)], their parents (n = 24) and available siblings (n = 7). The parental origins of the de novo rearrangements were assigned using molecular and cytogenetic analyses. Although not statistically significant, there was a two-fold increase in the number of paternally derived de novo rearrangements (n = 8) as compared with maternally derived rearrangements (n = 4). To distinguish between rob(21q21q) and i(21q), we used restriction fragment length polymorphisms (RFLPs) spanning the length of chromosome 21. Using all informative and partially informative RFLPs, we used the method of maximum likelihood to assign the most likely rearrangement definition (i or rob) and parental origin in each family. The maximum likelihood estimates indicated that all rearrangements tested (n = 8) were isochromosomes. C-banding revealed two centromeres in three cases indicating that a U-type exchange occurred between sister chromatids in these rearrangements. Our results suggest that the majority of de novo rea(21q21q) are isochromosomes derived from a single parental chromosome 21.     

Isolation of plasma membranes from cultured glioma cells and application to evaluation of membrane sphingomyelin turnover

A rapid and reliable method for the isolation of plasma membranes and microsomes of high purity and yield from cultured glioma cells is described. The procedure involves disruption by N2 cavitation, preliminary separation by centrifugation in Tricine buffer, and final separation on a gradient formed from 40% Percoll at pH 9.3. Enzyme and chemical markers indicated greater than 60% yield with six- to eightfold enrichment for plasma membranes and greater than 25% yield with three- to fourfold enrichment for a microsomal fraction consisting mainly of endoplasmic reticulum. The final fractions were obtained with high reproducibility in less than 1 h from the time of cell harvesting. Application of this procedure to human fibroblasts in culture is assessed. The isolation procedure was applied to investigations of synthesis and turnover of sphingomyelin and phosphatidylcholine in plasma membranes of glioma cells following incubation for 4-24 h with [methyl-3H]choline. These studies indicated that radioactivity from phosphatidylcholine synthesized in microsomes from exogenous choline may serve as a precursor of the head-group of sphingomyelin accumulating in the plasma membrane.     

Relative impacts of mortality factors in field populations of the waterstrider Gerris buenoi Kirkaldy (Heteroptera: Gerridae)

Summary Impacts of predators, food levels and cannibalism on population growth of G. buenoi were studied in two experiments using field exclosures. In the first experiment, experiments using field exclosures. In the first experiment, impacts of (1) predation by freshwater invertebrates and (2) food limitation on gerrid populations were considered in a 2 x 2 factorial design, using food supplements and elimination of predators as the experimental treatments. In the second experiment, the possible contribution of intraspecific predation to fitness of gerrid cannibals was assessed.Presence of invertebrate predators decreased egg-adult survivorship 2–3 fold and decreased the range of juvenile development times. The main predators noted in this study were fishing spiders (Dolomedes), backswimmers (Notonecta), larvae of predaceous diving beetles (Dytiscus), and dragonfly naiads (Aeshna). Food supplements, at 50–200% (by weight) of average natural surface fall, did not significantly effect survivorship but were associated with decreases in mean development time and with increases in whole body dry mass of teneral adults. Increases were greater for females than for males, suggesting that females are more likely to be protein limited under field conditions. Absence of predators was associated with smaller body size among teneral adults of G. buenoi, suggesting that screening out aquatic predators also had significant impact on food available to semi-aquatic bugs.Results of the second experiment demonstrate that the food cache hypothesis (Polis 1980) does not hold for G. buenoi. Neither survival to the adult stage nor dry mass of teneral males differed significantly between groups with or without access to early stages as potential prey. Dry mass of teneral females with access to younger stages during their own development was significantly less than for those without access to gerrid prey, suggesting that competition among stages for food was more important than cannibalism in, this experiment.A more comprehensive version of a paper presented at the XVII Int Cong Entomol, Hamburg, Federal Republic of Germany as part of a symposium entitled Phylogeny, Bionomics and Ecology of Waterstriders (Hemiptera, Gerridae)