A Mechanism of Energy Dissipation in Cyanobacteria

When grown under a variety of stress conditions, cyanobacteria express the isiA gene, which encodes the IsiA pigment-protein complex. Overexpression of the isiA gene under iron-depletion stress conditions leads to the formation of large IsiA aggregates, which display remarkably short fluorescence lifetimes and thus a strong capacity to dissipate energy. In this work we investigate the underlying molecular mechanism responsible for chlorophyll fluorescence quenching. Femtosecond transient absorption spectroscopy allowed us to follow the process of energy dissipation in real time. The light energy harvested by chlorophyll pigments migrated within the system and eventually reaches a quenching site where the energy is transferred to a carotenoid-excited state, which dissipates it by decaying to the ground state. We compare these findings with those obtained for the main light-harvesting complex in green plants (light-harvesting complex II) and artificial light-harvesting antennas, and conclude that all of these systems show the same mechanism of energy dissipation, i.e., one or more carotenoids act as energy dissipators by accepting energy via low-lying singlet-excited S₁ states and dissipating it as heat.     

The effects of pollution on Gammarus pulex (L) subsp,pulex (Schellenberg) in the inlet streams of Rostherne Mere,Cheshire

Two inlet streams, Rostherne Brook and the Southern Drain of Dolls Meadow, flowing into Rostherne Mere, Cheshire were sampled for macroinvertebrata, and their physical and chemical conditions analysed.The physical and chemical factors for these streams were similar, except for the stream beds and the pollution of Rostherne Brook. Both streams had large populations of Gammarus pulex and the life history of this organism was studied. The ratio of adult organism to juvenile diflered in the two streams, Rostherne Brook having a higher proportion of adults in winter and juveniles in summer as opposed to the Southern Drain in which a normal life history was exhibited.Experiments showed that these differences were not related to differences in stream bed conditions. It was considered that the different adult to juvenile ratios were therefore caused by pollution in Rostherne Brook. The juveniles were more tolerant to pollution and therefore more able to survive the summer when pollution effects were at a maximum.The life history was altered in Rostherne Brook by pollution. Instead of the dual life history produced by overwintering juveniles and speedy summer maturation, a simple alternation of juveniles and adults was seen.This change in life history enabled Gammarus to survive in the polluted waters of Rostherne Brook.

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Resume Deux débouchés de ruisseaux, Rostherne Brook et le Southern Drain de Doll's Meadow, qui coulent tous les deux dans le lac de Rostherne dans le Cheshire, ont été échantillonnés pour y trouver des macroinvertébrés, et pour en analyser les conditions physiques et chimiques.On a trouvé semblables les éléments physiques et chimiques de ces ruisseaux, à l'exception du lit des deux ruisseaux et de la pollution de Rostherne Brook.Les deux ruisseaux avaient une population nombreuse de Gammarus pulex dont on a étudié le cycle d'évolution. On a trouvé une proportion différente d'organismes adultes et jeunes dans les deux ruisseaux: Rotherne Brook a une plus grande proportion d'adultes en hiver et de jeunes en été, pendant que Southern Drain montre un cycle normal des organismes.Des expériences ont prouvés que ces différences n'avaient aucun rapport à des différences de conditions du lit des ruisseaux. On a considéré que la pollution de Rostherne Brook a donc causé les proportions différentes d'adultes et de jeunes. Les jeunes toléraient mieux la pollution et pouvaient donc mieux survivre à l'été quand les effets de la pollution étaient au maximum.Le cycle d'évolution était changé dans Rostherne Brook par la pollution. Au lieu du double cycle d'évolution produit par les jeunes qui passaient l'hiver et par un développement rapide en été, on a découvert uniquement l'alternation de jeunes et d'adultes.Ce changement du cycle d'évolution a permis au Gammarus de survivre dans les eaux corrumpues de Rostherne Brook.

     

Occurrence of poly-3-hydroxybutyrate inAzospirillum sp.

Azospirillum strains isolated from the roots and rhizosphere of some plants growing in West Bengal were subjected to qualitative and quantitative evaluation for poly-3-hydroxybutyrate (PHB) production. Out of the total 49 isolates, 13 (26%) were confirmed as PHB producers according to staining and chemical assay methods. The majority of these strains belonged toAzospirillum brasilense butA. amazonense andA. lipoferum were also present. When grown in the presence of NH₄Cl in the medium, the PHB content of the strains ranged from 1 to 14% of cell dry mass. The identity of the PHB extracted fromAzospirillum strain 24P-N-72 was confirmed by the characteristic UV and IR absorption peaks at 235 nm and 1730 cm⁻¹, respectively.     

Purified Fc epsilon R+ bone marrow and splenic non-B, non-T cells are highly enriched in the capacity to produce IL-4 in response to immobilized IgE, IgG2a, or ionomycin.

Non-B, non-T cells from spleen and bone marrow cells produce IL-4 in response to cross-linkage of high affinity receptors for Fc epsilon R or Fc gamma RII, and to treatment with calcium ionophores. Cells bearing high affinity Fc epsilon R constituted 1 to 2% of non-B, non-T cells of spleen and of total bone marrow cells from naive donors. In mice whose immune systems had been polyclonally activated by injection with anti-IgD antibodies or had been infected with Nippostrongylus brasiliensis larvae, the frequency of Fc epsilon R+ cells in splenic non-B, non-T cells was also 1 to 2% but in bone marrow from anti-IgD-injected mice donors the frequency was approximately 5%. Cell sorting experiments revealed that all of the capacity to produce IL-4 in response to immobilized IgE or IgG2a or to ionomycin was found in the Fc epsilon R+ fraction. Among the Fc epsilon R+ spleen cells from naive donors, the frequency of IL-4-producing cells was 1/20 to 1/40 whereas in mice that had been injected with anti-IgD or infected with N. brasiliensis, the frequency of IL-4 producing cells in the Fc epsilon R+ population was approximately 1/5.     

Early food production in Africa

The study of early food production in sub-Saharan Africa is at least as challenging as it is rewarding. Problems arise in large degree from the scarcity of relevant archeological material, particularly the remains of domesticated plants from prehistoric sites. This is attributable to several factors, including poor preservation, difficulties in recovering such material, and the limited amount of work so far invested in obtaining it. But, problems notwithstanding, fresh data and new methodological approaches have revealed aspects of early African food production that are interesting in themselves, as well as in global perspective. For example, contrary to what occurred in most other parts of the world, livestock herding in Africa often predated the earliest evidence of cultivation of domesticated plants. Moreover, the initial spread of food production throughout much of sub-Saharan Africa was accompanied by iron, rather than lithic, technology. This overview of current knowledge about early African food production is aimed at highlighting developmental patterns while also exposing limitations in our understanding of these patterns. Because of Africa's vast size, uniform coverage in reasonable depth of all parts of the continent is not possible. Thus, for example, I will not explicitly cover the complex neolithic record from Africa's Mediterranean region. Instead, I will generally concentrate on bodies of data and lines of investigation that characterize distinctive features of the African version of initial steps in raising crops and animals.