Germinability and enforced dormancy in seeds of species of indigenous grassland

Germination of seeds of a range of species from indigenous grassland was tested at an alternating temperature regime in incubators, soon after they were shed in 1978 and also after various intervals of dry storage at outdoor ambient temperatures. Concomitant investigations were made of seedling emergence from and seed survival at different depths of soil in pots; Poa annua and Poa trivialis were investigated separately in 1979. Almost all seeds of Lolium perenne, Cynosurus cristatus, Festuca rubra and Holcus lanatus germinated readily, but c. 30% of Deschampsia caespitosa seeds and c. 15% of fresh, early-shed Agrostis capillaris did not germinate until they were also given gibberellic acid. However, more late- than early-shed seed of the latter two species germinated and their seeds became more germinable with increasing length of storage. Of the dicotyledonous species tested, germination of Cerastium fontanum ssp. glabrescens was rapid and complete, but that of Ranunculus spp. was particularly protracted. All Ranunculus repens seeds and a large proportion of Ranunculus acris seeds were highly dormant. Species differed greatly in their ability to emerge from and persist at different depths in pots. The most persistent species after 15 months were R. repens (69%), A. capillaris (39%), Luzula campestris (37%), C. fontanum ssp. glabrescens (30%), P. trivialis (8%), D. caespitosa (7%) and H. lanatus (3%). A mean of 42% of P. annua and 16% of P. trivialis seeds persisted from autumn 1979 until late spring 1980, but pre-imbibing the seeds decreased seed persistence to 12% and 4% respectively. The results are discussed in relation to previously published information on the germination biology of the species and to the different abilities of the species to become part of the soil seed population.     

Chloride Electrochemical Potentials and Membrane Resistances in Nitella translucens

The chloride electrochemical potential difference between theinside of cells of Nitella translucens and the bathing mediumhas been measured by a direct electrical method employing Ag/AgClelectrodes. The membrane potential has been measured by meansof conventional salt bridge microelectrodes. These data havebeen used to calculate the internal chloride concentration ofthe cells; the mean value obtained was 39 mM. This chlorideelectrochemical potential difference has been short-circuitedthus causing an outward (depolarizing) electric current to flowthrough the cell membrane. The resulting membrane depolarizationhas been measured at two points along the length of the cellenabling the membrane resistance and space constant to be deduced;the respective values obtained were 24.8 Kcm² and 3.0 cm. Itis suggested that these experiments lend additional supportto the hypothesis that during the action potential in the Characeaethere occurs a transient increase in the chloride conductanceof the plasmalemma.     

Electrical Potentials and Na, K, and Cl Concentrations in the Vacuole and Cytoplasm of Nitella translucens

The potential differences across the tonoplast and plasmalemmamembranes have been measured in the single cells of Nitellatranslucens, the cells being immersed in an artificial pondwater (composition: NaCl _1.0 mM., KC1 _0.1 mM., CaCl₂, _0.1 mM.).The potential of the cytoplasm is –138 m V with respectto the bathing medium and –18 mV with respect to the vacuole.The concentrations of Na, K, and Cl have been measured in thetwo cell fractions. The concentrations in the flowing cytoplasmare: Na 14 mM., K 119 mM., and Cl 65 mM.; the vacuolar concentrationsare: Na 65 mM., K 75 mM.,and Cl 160 mM. The observed potential differences across the two membranesare compared with the Nernst potentials for all three ions.This analysis shows that all three ions are actively transportedat the plasmalemma: Na is pumped outwards while K and Cl arepumped inwards. At the tonoplast Na is pumped into the vacuolewhile K and Cl are close to electrochemical equilibrium. The inhibitor, ouabain, has no effect on the cell resting potential.     

THE EFFECT OF CERTAIN SOIL TREATMENTS ON DIDYMELLA STEM-ROT OF TOMATOES

About 93% of Didymella lycopersici spores were destroyed after 4 weeks incubation in unsterilized soil. A survey of the microflora of glasshouse soil receiving different treatments and inoculated with D. lycopersici showed no clear relation between numbers of any group of organisms and the incidence of stem rot. Sterilized soil was not made toxic to D. lycopersici by the growth of a number of soil microorganisms even after 9 months incubation, but addition of unsterilized soil or of a suspension of unsterilized soil quickly restored toxicity. Direct observations of spores in soil on slides showed that their fate varied with the treatment of the soil before inoculation. With fresh soil or air-dry soil moistened 2 or more days before inoculation, lysis of spores occurred. With air-dry soil moistened and inoculated simultaneously, some spores germinated but growth of germ tubes soon ceased. No direct connexion could be seen between the fate of the spores and soil microorganisms. Addition of glucose to unsterilized soil reduced its toxicity to D. lycopersici. Soils steamed for 1 min. or longer were not toxic to D. lycopersici , but soils steamed for very short periods were as toxic as unsterilized soils although the soil microflora was much reduced.     

Comparison of 5′-Nucleotidase Activities Among Cultured Murine Melanoma Cell Lines

The activity of 5′-nucleotidase and ouabain-sensitive Na/K ATPase was determined in seven different mouse melanoma cell lines. Ouabain-sensitive Na/K ATPase activity was found in NP40-treated cell homogenates of all cell lines. However, 5′-nucleotidase activity was found in only one mouse melanoma cell line—JB/RH. The absence of expression of 5′-nucleotidase activity in the other six cell lines is not associated with pigmentation in melanoma cells, nor is the gene switched off in all transformed melanocytes of C57BL/6 origin.     

ATPase and Proton-Translocating Activities in a Plasma Membrane-Enriched Fraction from Cotyledons of Ricinus communis

Sucrose gradient centrifugation was used to separate the microsomalmembranes and purify the plasma membrane ATPase from Ricinuscotyledons. The pellet from a three-step (30, 34, 38%) sucrosegradient was enriched in plasma membrane as determined by acombination of marker assays. The partially purified plasma membrane ATPase was magnesium-dependentand had a pH optimum of 6.5. It showed high sensitivity to vanadate,erythrosin B, SW 26, DCCD and PCMBS but low sensitivity to azide,nitrate and NEM. Substitution of calcium for magnesium resultedin low activity, and in the presence of magnesium, calcium wasinhibitory. KCl stimulation was low (less than 50%) and of thepotassium salts tested all were stimulatory except which was inhibitory. Specificity for nucleotide triphosphateswas high, greatest activity occurring with ATP. Proton-pumping activity measured using quinacrine fluorescencequenching was inhibited by vanadate and erythrosin B but notby nitrate and oligomycin indicating that activity was mainlydue to the plasma membrane ATPase. Key words: ATPase, cotyledons, plasma membrane, proton pumping, Ricinus communis     

Lingulid shell mediation in clay formation

Organophosphatic shells of the brachiopod Lingula squarniformis , collected from Scottish Lower Carboniferous shales and mudstones of intertidal to sublittoral provenance, have been studied to ascertain chemico-structural changes resulting from fossilization. Enough original shell has been preserved at ultrastructural and molecular levels to confirm that Carboniferous and Recent integuments are homologous with stratiform successions of apatitic to organic laminae forming rhythmic sets. One of the main organic constituents, the acidic, hydrophilic gel glycosaminoglycans (GAGs), is the dominant component towards the tops of rhythms. During fossilization of the Carboniferous shells, GAGs degraded incrementally without disturbing apatitic ultrastructures, and the spaces so created became partly filled with sheets of recrystal-lized apatite with some kaolinite or with books and plates of kaolinite. The kaolinite in the shells contrasts with the illite of the entombing sediments and suggests that degrading acidic GAGs mediated in clay formation in situ . The sediments also contain framboidal pyrite, which is virtually absent from the shells themselves but is usually even more abundant, with a greater range of trace metals, in the sedimentary fills of complete shells. This imbalance suggests mediation by another gel, the glycocalyx, secreted by the inner epithelium of the brachiopod mantle. The glycocalyx would have lined the shell interior and could have served as a sorption film for dissolved metals precipitated as compounds on decomposition of body tissue.     

Colonization dynamics of river benthos in response to local changes in bed characteristics

1. The effects of small-scale variation in the nature of a river bed upon the colonization dynamics of benthic invertebrates were explored through a series of microhabitat implants placed in a small river in southern Ontario. The implants presented variations in the levels of four microhabitat features: substrate particle size, current regime, added food and light. The sixteen possible combinations of these variables were replicated five times, for a total of eighty implants.
2. After 14 days of exposure, some of the controlled variables had been modified and a number of other variables (sand, fine (FPOM) and coarse (CPOM) particulate organic matter) had been added by the river.
3. Benthic diversity differed among the implants, with sand and CPOM accounting for 15.5% of the variation. Benthic density was more uniform and was weakly related only to added food. Application of the CANOCO program to the data set suggested that, in general, the environmental variables manipulated in this study were not the key factors influencing colonization, although they may have been important in non-linear combination.
4. A number of important positive associations were evident among colonizing species, some of which are thought to reflect those of predator and prey.
5. Control of colonization appears to be through multiple factors (abiotic, biotic, autochthonous, allochthonous) that differ in nature according to species, and which underline the complexity of selection responses of individual taxa to local variations in bed structure. Researchers must acknowledge this multifactorial organization and dynamic nature if workable models of lotic community structure and development are to be forthcoming.