Modification of excitation energy distribution to photosystem I by protein phosphorylation and cation depletion during thylakoid biogenesis in wheat

The effects of protein phosphorylation and cation depletion on the electron transport rate and fluorescence emission characteristics of photosystem I at two stages of chloroplast development in light-grown wheat leaves are examined. The light-harvesting chlorophyll a/b protein complex associated with photosystem I (LHC I) was absent from the thylakoids at the early stage of development, but that associated with photosystem II (LHC II) was present. Protein phosphorylation produced an increase in the light-limited rate of photosystem I electron transport at the early stage of development when chlorophyll b was preferentially excited, indicating that LHC I is not required for transfer of excitation energy from phosphorylated LHC II to the core complex of photosystem I. However, no enhancement of photosystem I fluorescence at 77 K was observed at this stage of development, demonstrating that a strict relationship between excitation energy density in photosystem I pigment matrices and the long-wavelength fluorescence emission from photosystem I at 77 K does not exist. Depletion of Mg²⁺ from the thylakoids produced a stimulation of photosystem I electron transport at both stages of development, but a large enhancement of the photosystem I fluorescence emission was observed only in the thylakoids containing LHC I. It is suggested that the enhancement of PS I electron transport by Mg²⁺-depletion and phosphorylation of LHC II is associated with an enhancement of fluorescence at 77 K from LHC I and not from the core complex of PS I.     

The use of historical environmental monitoring data to test predictions on cross-scale ecological responses to alterations in river flows

Determination of ecological responses to river flows is fundamental to understanding how flow-dependent ecosystems have been altered by regulation, water diversions and climate change, and how to effect river restoration. Knowledge of ecohydrological relationships can support water management and policy, but this is not always the case. Management rules have tended to be developed ahead of scientific knowledge. The lag between practice and knowledge could be addressed by using historical monitoring data on ecological responses to changes in flows to determine significant empirical ecohydrological relationships, as an adjunct to investigating responses prospectively. This possibility was explored in the Murray–Darling Basin, Australia. We assessed 359 data sets collected during monitoring programs across the basin. Of these, only 32 (9%) were considered useful, based on a match between the scale at which sampling was done and ecological responses are likely to occur, and used to test flow–ecology predictions for phytoplankton, macroinvertebrates, fishes, waterbirds, floodplain trees, basin-scale vegetation and estuarine biota. We found relationships between flow and ecological responses were likely to be more strongly supported for large, long-lived, widespread biota (waterbirds, basin-scale vegetation, native fishes), than for more narrowly distributed (e.g. estuarine fishes) or smaller, short-lived organisms (e.g. phytoplankton, macroinvertebrates). This pattern is attributed to a mismatch between the design of monitoring programs and the response time frames of individual biota and processes, and to the use of local river discharge as a primary predictor variable when, for many biotic groups, other predictors need to be considered.     

Design and implementation of degenerate microsatellite primers for the mammalian clade

Microsatellites are popular genetic markers in molecular ecology, genetic mapping and forensics. Unfortunately, despite recent advances, the isolation of de novo polymorphic microsatellite loci often requires expensive and intensive groundwork. Primers developed for a focal species are commonly tested in a related, non-focal species of interest for the amplification of orthologous polymorphic loci; when successful, this approach significantly reduces cost and time of microsatellite development. However, transferability of polymorphic microsatellite loci decreases rapidly with increasing evolutionary distance, and this approach has shown its limits. Whole genome sequences represent an under-exploited resource to develop cross-species primers for microsatellites. Here we describe a three-step method that combines a novel in silico pipeline that we use to (1) identify conserved microsatellite loci from a multiple genome alignments, (2) design degenerate primer pairs, with (3) a simple PCR protocol used to implement these primers across species. Using this approach we developed a set of primers for the mammalian clade. We found 126,306 human microsatellites conserved in mammalian aligned sequences, and isolated 5,596 loci using criteria based on wide conservation. From a random subset of ~1000 dinucleotide repeats, we designed degenerate primer pairs for 19 loci, of which five produced polymorphic fragments in up to 18 mammalian species, including the distinctly related marsupials and monotremes, groups that diverged from other mammals 120-160 million years ago. Using our method, many more cross-clade microsatellite loci can be harvested from the currently available genomic data, and this ability is set to improve exponentially as further genomes are sequenced.     

Structure of the cyanobacterial Magnesium Chelatase H subunit determined by single particle reconstruction and small-angle X-ray scattering

The biosynthesis of chlorophyll, an essential cofactor for photosynthesis, requires the ATP-dependent insertion of Mg²⁺ into protoporphyrin IX catalyzed by the multisubunit enzyme magnesium chelatase. This enzyme complex consists of the I subunit, an ATPase that forms a complex with the D subunit, and an H subunit that binds both the protoporphyrin substrate and the magnesium protoporphyrin product. In this study we used electron microscopy and small-angle x-ray scattering to investigate the structure of the magnesium chelatase H subunit, ChlH, from the thermophilic cyanobacterium Thermosynechococcus elongatus. Single particle reconstruction of negatively stained apo-ChlH and Chl-porphyrin proteins was used to reconstitute three-dimensional structures to a resolution of ∼30 Å. ChlH is a large, 148-kDa protein of 1326 residues, forming a cage-like assembly comprising the majority of the structure, attached to a globular N-terminal domain of ∼16 kDa by a narrow linker region. This N-terminal domain is adjacent to a 5 nm-diameter opening in the structure that allows access to a cavity. Small-angle x-ray scattering analysis of ChlH, performed on soluble, catalytically active ChlH, verifies the presence of two domains and their relative sizes. Our results provide a basis for the multiple regulatory and catalytic functions of ChlH of oxygenic photosynthetic organisms and for a chaperoning function that sequesters the enzyme-bound magnesium protoporphyrin product prior to its delivery to the next enzyme in the chlorophyll biosynthetic pathway, magnesium protoporphyrin methyltransferase.     

Male-biased operational sex ratios and the Viking phenomenon: an evolutionary anthropological perspective on Late Iron Age Scandinavian raiding

In this paper, we use a combination of evolutionary theory, ethnographic data, written sources, and archaeological evidence to develop a new explanation for the origins of Viking raiding. Our argument focuses on the operational sex ratio, which is the ratio of males to females in a society who are ready to mate at a given time. We propose that a combination of two practices – polygyny and concubinage – and the increase in social inequality that occurred in Scandinavia during the Late Iron Age resulted in a male-biased operational sex ratio. This would have created a pool of unmarried men motivated to engage in risky behaviours that had the potential to increase their wealth and status, and therefore their probability of entering the marriage market. With high-status men looking to instigate expeditions to acquire plunder and develop their reputations as war leaders, raiding represented a mutually beneficial means of achieving social advancement and success.     

Evidence for two distinct origins of replication in the large endogenous plasmid of Anacystis nidulans R2

Summary Shuttle cloning vectors, capable of replication in Escherichia coli and in the cyanobacterium Anacystis nidulans R2, have been used to localize a putative origin of replication of the large endogenous plasmid (pANL) of A. nidulans R2. Utilizing the cloning flexiblity of the polylinker containing E. coli plasmid pDPL 13, we have constructed a series of deletion derivatives of a 11.7 kilobase segment of pANL believed to contain a functional origin of replication. Two distinct segments of pANL that are 5.7 and 4.7 kilobases in size carry sufficient information to support transformation of A. nidulans R2. These DNA fragments, designated by us ORI 1 and ORI 2, do not overlap and show no DNA homology by blot hybridization analysis. Additionally, neither of these fragments are homologous to the replication origin of the other endogenous plasmid (pANS) of A. nidulans R2. Intact hybrid plasmids capable of transforming A. nidulans R2 have been re-isolated from transformed cells indicating that these plasmids exist autonomously in both A. nidulans R2 and E. coli.Dedicated to Professor Georg Melchers to celebrate his 50-year association with the journal     

The maturation state of three types of granulocyte/macrophage progenitor cells from mouse bone marrow

The progenitor cells of neutrophil granulocytes and macrophages which are able to proliferate and differentiate in vitro (CFU-c) form a heterogeneous population. By the use of specific colony stimulating activities and cell separation by equilibrium density centrifugation, three subpopulations of CFU-c can be detected. These three CFU-c are characterized by buoyant densities of 1.070, 1.075 and 1.080 g.cm^?3 and by their proliferative response to 18 h postendotoxin serum, colony stimulating factor from extracts of mouse embryos and uteri (CSF-pmue) and erythrocyte lysate, respectively. The three CFU-c are compared with respect to their differentiation potential, the maturation rate of their progeny cells and their proliferation capacity. It is shown that with increasing density of the CFU-c the maturation rate increases (sequential maturation of colonies derived from CFU-c with densities of 1.080, 1.075, 1.070 g.cm^?3) and the proliferation capacity decreases (colony size decreases in the sequence of CFU-c with densities 1.070, 1.075, 1.080 g.cm^?3). Concerning the differentiation potential it is shown that all three CFU-c detected have the capacity to form granulocytes as well as macrophages. On the basis of these results it is concluded that the CFU-c with densities of 1.070, 1.075 and 1.080 g.cm^?3 represent a maturation sequence.