Paraquat tolerant and susceptible perennial ryegrasses: effects of paraquat treatment on carbon dioxide uptake and ultrastructure of photosynthetic cells

Abstract. Paraquat treatment of susceptible Lolium perenne seedlings (cultivar Kent Indigenous) rapidly inhibited CO₂ uptake and after 1 h chloroplasts exhibited abnormal fusions of the thylakoid membranes. Further ultrastructural changes occurred within the chloroplasts until 8 h after treatment, when cytoplasmic damage also became evident. The localization of primary damage within the chloroplast differs from previous reports of paraquat toxicity in other species. Paraquat treatment of tolerant L. perenne seedlings (line PRP IX) resulted in little change in CO₂ uptake and ultrastructural effects were generally confined to the gradual development of deposits in the chloroplast stroma. These observations are discussed in relation to the mechanism of action of the herbicide and the proposed mechanism of paraquat tolerance in L. perenne.     

Variable microsatellite loci isolated from the azure damselfly,Coenagrion puella (L.) (Zygoptera; Coenagrionidae)

We isolated and characterized 10 polymorphic microsatellite loci from the azure damselfly Coenagrion puella (Zygoptera; Coenagrionidae) as part of a study assessing reproductive success and genetic structure in an isolated population of this species. Levels of genetic diversity were assessed in 50 individuals collected from Queen Elizabeth Country Park, Hampshire, UK. The number of alleles per microsatellite loci ranged from three to 22 and the observed and expected heterozygosities varied between 0.26 and 0.84 and between 0.23 and 0.91, respectively. Two loci showed significant (P < 0.05) heterozygote deficits, likely because of null (non‐amplifying) alleles; one pair of loci was in linkage disequilibrium.     

Seronera bull problem: The trees

(1) The impact of groups of bull elephants on the wooded–grassland of the Seronera area of the Serengeti National Park, Tanzania, is examined. (2) Elephant use of trees occurs contagiously. At use loci in the woodlands, removal of canopy–forming acacia has been as high as 6% per annum. (3) However, from a survey of the whole Seronera woodland community, the loss of large trees has been 2–5% per annum. (4) It is argued that the regeneration potential is adequate to compensate loss due to elephant activity, and that large acacia will not disappear because of elephants. (5) Management action is discussed and recommendations made.     

The Influence of Composition of the Basal Medium on the Growth and Morphogenesis of Cultured Sitka Spruce (Picea sitchensis) Tissues

In vitro culture of Picea sitchensis (Bong.) Carr. needle explantson a number of basal culture media indicated that a complexmixture of organic additives was neither essential nor stimulatory.Adventitious bud production occurred at inorganic nitrogen levelsof 15–60 x 10^–3M and 7.5–30 x 10^–3 Min the adventitious bud induction and elongation media, respectively,when a well-balanced ratio of NH₄⁺:NO₃^– was maintained.However, necrosis was increased at the highest level of inorganicnitrogen. Organogenesis was more sensitive to changes in theratio of NH₄⁺:NO₃^–. Complete replacement of NH₄⁺ withNO₃^– during the adventitious bud induction passage severelyinhibited organogenesis, indicating that a reduced form of nitrogenmay be essential for adventitious bud differentiation. Conversely,a high proportion of NH₄⁺ in either the adventitious bud inductionor elongation medium increased tissue necrosis and inhibitedbud induction, reflecting the potential toxicity of this ion.Explants from different individual trees were found to varyconsiderably in their morphogenetic responses, but NH₄⁺:NO₃^–ratios of 1:5 or 1:2 were o ptimal for all individual treeswhich developed adventitious buds from needle cultures. Picea sitchensis, Sitka spruce, tissue culture, nitrogen     

Effects of plant diversity and structural complexity on parasitoid behaviour in a field experiment

1. In natural ecosystems, plants containing hosts for parasitoids are often embedded within heterogeneous plant communities. These plant communities surrounding host‐infested plants may influence the host‐finding ability of parasitoids. 2. A release‐recapture‐approach was used to examine whether the diversity and structural complexity of the community surrounding a host‐infested plant influences the aggregation behaviour of the leaf‐miner parasitoid Dacnusa sibirica Telenga and naturally occurring local leaf‐miner parasitoids. Released and locally present parasitoids were collected on potted Jacobaea vulgaris Gaertn.plants infested with the generalist leaf‐miner Chromatomyia syngenesiae Hardy. The plants were placed in experimentally established plant communities differing in plant diversity (1–9 species) and habitat complexity (bare ground, mown vegetation, and tall vegetation). Additionally, parasitoids were reared out from host mines on the trap plants. 3. Plant diversity did not influence the mean number of recaptured D. sibirica or captures of other locally present parasitoids but the number of recaptured parasitoids was influenced by habitat complexity. No D. sibirica parasitoids were recaptured in the bare ground plots or plots with mown vegetation. The mean number of recaptured D. sibirica generally increased with increasing complexity of the plant community, whereas locally present parasitoids were captured more frequently in communities with more bare ground. There was a unimodal relationship between the number of reared out parasitoids and diversity of the surrounding vegetation with the highest density of emerged parasitoids at intermediate diversity levels. 4. The present study adds to the thus far limited body of literature examining the aggregation behaviour of parasitoids in the field and suggests that the preference of parasitoids to aggregate in complex versus simple vegetation is association specific and thus depends on the parasitoid species as well as the identity of the plant community.     

Herd-level risk factors associated with the presence of Phage type 21/28 E. coli O157 on Scottish cattle farms

Background  

E. coli O157 is a bacterial pathogen that is shed by cattle and can cause severe disease in humans. Phage type (PT) 21/28 is a subtype of E. coli O157 that is found across Scotland and is associated with particularly severe human morbidity.     

The Translocation of 14C-Photoassimilate from Normal and Mutant Leaves to the Pods of Pisum sativum L.

In experiments using radioactive carbon dioxide (¹⁴CO₂) a comparisonwas made of the ¹⁴C-photoassimilate translocation potentialsof two normal leaved (genotype AfAfTlTl) and two mutant formsof Pisum sativum (pea). A ¹⁴CO₂ administration method is describedthat permitted ¹⁴C-translocation studies to be conducted underfield conditions. One of the mutants available produced tendrils in place of leaves(afafTlTl). The other mutant studied was without tendrils buthad a much branched petiole with numerous relatively minuteleaflets (afaftltl). These mutants and the normal-leaved cultivarswith which they were compared were not isogenic lines. Lengthybackcrossing would be required before full assessment couldbe made of the possible agronomic value of such mutations. An interim evaluation of these mutants was based on ¹⁴C-distributionassays that were conducted 48 h after feeding ¹⁴CO₂, to specifiedleaves. The indication was that in translocation terms the leafand pod had a well defined respective source and sink relationshipthat was independent of leaf morphology. In each case the podswhich constituted the major ¹⁴C sinks depended on which leafhad been fed ¹⁴CO₂. With regard to sink specific activity asdefined by the quantity of ¹⁴C incorporated per unit dry weightof pod, the mutants were not significantly different from normal. The implication of these findings was that fundamental changesin pea leaf morphology could be made genetically without a markedeffect on the photoassimilate export potential of the leaf.