Inhibition of Photosynthesis in Barley with Decreased Levels of Chloroplastic Glutamine Synthetase Activity

Mutant barley plants containing only 8%, 16% or 38% of the wildtype level of glutamine synthetase activity have been isolated.The level of glutamine synthetase activity in the roots of themutant containing only 8% leaf activity was not affected bythis mutation. The plants accumulated high levels of ammoniain leaves exposed to air and although they were able to carryout photosynthetic CO₂fixation normally at low levels of atmosphericO₂, they were unable to maintain wild type rates of CO₂fixationin air. The extent of this inhibition and the extent to whichammonia accumulated in the leaves was dependent on the photonfluence rate intercepted by the plant. When leaves from themutant plant were fed glutamine under non-photorespiratory conditionsfor 40 min before they were transferred to air, the plants exhibitedwild type rates of CO₂ fixation in air but the ammonia contentof the leaves increased to an even higher level. At least inthe short term, therefore, ammonia accumulation was not responsiblefor the dramatic decline in the fixation rate of these mutantsin air. The most probable explanation is that as the supplyof potential amino donors diminished on transfer to air, therewas a restriction on the return of glycerate to the Calvin cyclewithin the chloroplast. Key words: Ammonia toxicity, photorespiration, photosynthesis, GS-deficient barley     

The response of Norway spruce seedlings to simulated acid mist

Four pot experiments are reported in which Norway spruce ( Picea abies (L.) Karst) seedlings, of different nutrient status, were treated with acid mist for one growing season in open-top chambers (OTCs). Combinations of H⁺, SO₄²⁻, NH₄⁺ and NO₃⁻ were applied at different frequencies of application and supplying different doses of S and N kg ha⁻¹. Plant growth, visible injury, frost hardiness and nutrient status were observed. These experiments were undertaken to improve our understanding of the interaction of environmental factors such as nutrition and mist-exposure frequency on seedling response to N and S deposition.
Both acidity (pH 2·7) and SO₄²⁻ ions were necessary to induce visible injury. Mist containing SO₄²⁻, H⁺ and to a lesser extent NH₄⁺ significantly reduced winter frost hardiness. Increasing the misting frequency, and to a lesser extent the overall dose, increased the likelihood of acid mist causing visible injury and reducing frost hardiness. Post-planting stress, low N status and needle juvenility increased the likelihood of acid mist causing visible injury. Increased plant vitality, adequate N status and growth rate reduced the likelihood of acid-mist-induced reductions in frost hardiness.
Principles underlying the responses of spruce seedlings treated in controlled conditions to acid mist are discussed.     

Identification of a Microsporidian Polar Tube Protein Reactive Monoclonal Antibody

ABSTRACT. The microsporidia are characterized by spores containing a single polar tube that coils around the sporoplasm. When triggered by appropriate stimuli, the polar tube rapidly discharges out of the spore forming a hollow tube. The sporoplasm passes out of the spore through this tube serving as a unique vehicle of infection. Due to the unusual functional and solubility properties of the polar tube, the proteins comprising it are likely to be members of a protein family with a highly conserved amino acid composition among the various microsporidia. Polar tube proteins were separated from the majority of other proteins in glass bead disrupted spores of Glugea americanus using sequential 1% sodium dodecyl sulfate (SDS) and 9M urea extractions. The resultant spore pellet demonstrated broken, empty spore coats and numerous polar tubes in straight and twisted formations by negative stain transmission electron microscopy. After subsequent incubation of the pellet with 2% dithiothreitol (DTT), empty spore coats were still observed but the polar tubes were no longer present in the pellet. The DTT supernatant demonstrated four major protein bands by SDS-PAGE: 23, 27, 34 and 43 kDa. Monoclonal antibodies were produced to these proteins using Hunter's Titermax adjuvant. Mab 3C8.23.1 which cross-reacted with a 43-kDa antigen by immunoblot analyis, demonstrated strong reactivity with the polar tube of G. americanus spores by immunogold electron microscopy. This antibody will be useful in further characterization of polar tube proteins and may lead to novel diagnostic and therapeutic reagents.     

Transformation and Productive Infection of Human Osteosarcoma Cells by a Feline Sarcoma Virus

FELINE sarcoma virus (FSV) transforms human embryo cells in vitro¹; it therefore seemed interesting to determine whether this virus could transform human osteosarcoma cells. Defective Moloney sarcoma virus genome can be rescued from non-producer hamster tumour cells by feline leukaemia virus (FeLV)² and because FSV stocks also contain excess FeLV (ref. 1 and unpublished observations of R. V. G.), it was hoped that human osteosarcoma cells transformed by FSV and co-infected with FeLV might yield a human sarcoma virus.     

Inhibitor of the DNA-dependent DNA Polymerase of Some RNA Tumour Viruses in Feline Sera

AN inhibitor of the RNA-dependent DNA polymerases^1,2 of mammalian C-type viruses was found in sera from rats bearing transplantable tumours, induced by murine C-type RNA tumour viruses^3,4. Partially purified polymerases of murine leukaemia virus³ and feline leukaemia virus (FeLV)⁴ were shown to be antigenic in rabbits and a rat, respectively. We have detected an inhibitor of the DNA-dependent DNA polymerase^5,6 of feline and murine C-type viruses in the sera of cats inoculated in utero and/or postnatally with the Gardner-Arnstein strain of feline sarcoma virus (FSV)⁷ and in the sera of cats bearing spontaneous sarcomas, lymphomas or carcinomas.     

THE FORAMINIFERA OF THE HYPERSALINE ABU DHABI LAGOON, PERSIAN GULF

Living foraminifers were found associated with seaweed, seagrass, dead coral, crust, and sediment substrates in the hypersaline Abu Dhabi lagoon. Peneroplis planatus is the most abundant living species and it is the most conspicuous dead form in the carbonate sediments. In common with other lagoons of this type, diversity is low and there is a dominance of Miliolina and Rotaliina. The Abu Dhabi lagoon is a modern analogue of fossil lagoonal sediments from the Meso-zoic and Tertiary of Arabia.     

Water stress,transpiration and leaf area index in eucalypt plantations in a bauxite mining area in south-west Australia

The clearing of native forests for open cut mining for bauxite is a potential cause for severe modification of the hydrological cycle. In the Darling Range, Western Australia, jarrah (Eucalyptus marginata Sm.) woodlands are being cleared for mining and are being replaced with plantations of other eucalypts. The plantation trees, which were up to 8 years old, showed no greater water stress than those of the original forest. The leaf area index of older plantation trees was usually higher than that of the original, mature forest. Transpiration rate was estimated on twigs enclosed briefly in a transpiration chamber. Prior test showed that this method was appropriate for comparisons in field grown eucalypts. Field measurements of stratified samples showed little difference in transpiration rate per unit leaf area between plantation forests and original forests. For the last 3 months of the dry season, however, transpiration per unit area of leaves was depressed by 25% in the plantation forest.     

Hybridization between tetraploid species of Alopecurus L. (Poaceae): morphological studies of natural and artificial hybrids

The morphology of individuals of mixed natural populations of three species of Alopecurus, A. pratensis, A. geniculars and A. arundinaceus , is described. It is suggested that plants morphologically intermediate between the parental species are hybrids or of hybrid origin. Hybridization occurs more readily between A. pratensis and A. arundinaceus than between A. pratensis and A. geniculate , since intermediate forms were recovered from all mixed populations of A. pratensis and A. arundinaceus. The intermediate forms occur only in a few populations of A. pratensis and A. geniculars where an appropriate habitat is available. Evidence of backcrossing and therefore introgression comes from the continuum of intermediate forms that exists between the species. Scatter diagrams for individual populations show distinct differences in the degree of introgression. Observations on artificially produced hybrids are similar to those on naturally occurring hybrids.