The effect of methanogen growth on mineral substrates: will Ni markers of methanogen‐based communities be detectable in the rock record?

Methanogens, thought to be present on early Earth, have a high requirement for Ni, suggesting that Ni utilization could be a potential biosignature for methanogens if enhanced Ni extraction from surrounding minerals accompanies methanogenic growth. To test the potential for such Ni extraction from minerals by methanogens, Ni release from Ni‐containing silicate glass was measured in Ni‐free growth medium in the presence of the methanogen Methanothermobacter thermoautotrophicus (average pH ∼7.0) and observed to be higher than an abiotic control (average pH ∼6.8). However, batch dissolution experiments and a siderophore assay indicate that cell exudates such as siderophores, low molecular weight organic acids, or lysates accompanying cell death are not responsible for the observed increase in Ni release rate. In addition, scanning electron microscopy (SEM) shows little to no evidence of direct microbe–mineral interactions such as biofilms or pitting. Instead, comparison with abiotic experiments suggests that changes in pH due to CO₂ uptake may be responsible for enhanced dissolution in the presence of metabolizing cells. These results document that methanogens may not preferentially extract Ni from surrounding minerals although they may indirectly affect mineral reaction rates that are pH sensitive. Thus identifiable Ni biosignatures may not exist in the rock record to document the presence of methanogens on early Earth or Mars.     

Development of ovule and seed in Rapateaceae

VENTURELLI, M. & BOUMAN, F., 1988. Development of ovule and seed in Rapateaceae. The structure of the ovules and/or seeds of twelve species of Rapateaceae were studied, some additional embryological characters also being recorded. The ovules are always anatropous, bitegmic and crassinucellate, but they differ in the shape, size and in thickness of the outer integument. In Rapateaceae the outer integument is initiated subdermally. The seed coat of the Rapateaceae shows two mechanical layers: an endotesta with silica present as bodies or as incrustations in cell walls, in conjunction with an exotegmen with a jigsaw cell pattern complicated by a labyrinth-like sculpturing of the outer cell walls. The innermost layer of the inner integument is tanniniferous. Large hilar scars with tracheidal plates on the corresponding fruit wall and a persistent obturator are recorded in Rapateaceae. On the basis of embryological characters the family fits well into the Commelinales. Testa structure most closely resembles that of the Commelinaceae. The differences in ovule and seed structure agree with the currently accepted tribal classification.     

Shingle-based wetlands at Dungeness

WATERS, S. J. P. & FERRY, B. W., 1989. Shingle-based wetlands at Dungeness . At Dungeness, a unique development of open water and natural wetland has occurred on the shingle beaches. Over 700–1000 years, low-lying areas have changed from saline lagoons into freshwater lakes which are now largely infilled by reedswamp and sallow carr. Since about 1970, the water-table has been lowered, by a combination of water abstraction and hydrological changes associated with gravel extraction. Water-table lowering has accelerated colonization by reedswamp and sallow carr, and has caused loss of sedge-rich marshland. Possible methods are suggested for promoting development of such marshland in artificial excavations.     

Structure and Macromolecular Composition of the Seed Coat of the Musaceae

Mature seed coats of representatives of all three genera ofMusaceae were analysed for macromolecular composition with variousmass spectrometric techniques and compared with scanning electronmicroscopy and light microscopy in combination with histochemicaltechniques. Mass spectrometric techniques are more sensitiveand more specific in identifying macromolecular compounds thanhistochemical methods. The macromolecular ‘fingerprint’of the seed coats of Musaceae showed unique components of aromaticphenols. The seed coat structure of all three genera is homogeneouswithin the Musaceae. It is characteristic at the family leveland most complex within the Zingiberales. Very remarkable arethe separation of the outer cell walls from the exotestal layer,exposing a secondary surface with silica crystals, and the relativelythick mesotesta which protects the seed, e.g. against the bitingforces and passage through the digestive tracts of dispersingagents. Germination takes place with an operculum and is facilitatedby a predetermined rupture layer in the micropylar collar. Themusaceaous seed presents a good example of the solution of conflictingdemands of protection and germination. Musaceae; Musa; Ensete; Musella; seed coat; pyrolysis (gas chromatography) mass spectrometry; histochemistry; anatomy; macromolecules; silica; lignin; cellulose; vegetable polyphenols; operculum; germination     

The Effects of Simazine, Applied for Weed Control, on the Mycorrhizal Development of Pinus Seedlings

The herbicide Simazine is widely used in forestry nurseries.Its effect on the incidence of ectomycorrhizae on pine seedlingroot systems was investigated. Under field (nursery) conditions,at routine rates of application, Simazine does not inhibit mycorrhizaldevelopment in Pinus sylvestris and P. nigra, and it may, undersome conditions, actually enhance mycorrhizal formation. Sucha stimulatory effect was also obtained with pot-grown seedlingstreated with the herbicide. It is suggested that soil type andclimatic factors might be involved in determining the responseto Simazine. The mode of stimulation of mycorrhizal developmentby this herbicide is not understood, but it is not via suppressionof weed growth. Pinus sylvestris, Pinus nigra, pine seedlings, ectomycorrhizae, Simazine