Analysis of Light-Induced Depressions of Photosynthesis in Leaves of a Wheat Crop during the Winter

The photosynthetic performances of individual leaves of a wheat (Triticum aestivum cv Bezostaya) crop were assessed daily and throughout individual days during the winter when temperature and light levels were fluctuating. Measurements of chlorophyll fluorescence induction and the maximum quantum yield of O₂ evolution were made on individual leaves. Depressions in the ratio of variable to maximal fluorescence (F_v/F_m) were correlated with low temperatures and high light levels throughout the winter and during the course of individual days. Depressions in F_v/F_m observed in the field during the day were not accompanied by any significant change in the ability of photosystem II complexes to bind 3-(3,4-dichlorophenyl)-1-dimethyl urea, indicating that the depressions in F_v/F_m were not attributable to photodamage to the D1 protein of the photosystem II reaction center. Decreases in F_v/F_m were associated with increases in the rate of dissipation of excitation energy by radiationless decay processes and decreases in the quantum efficiency of CO₂ assimilation, indicative of a rapidly reversible light-induced “downregulation” of photosynthesis. No major changes were observed in the maximum quantum efficiency of O₂ evolution of leaves throughout periods of fluctuating temperature and light, because light-induced depressions in photosynthetic efficiency recovered within the time required to make these measurements.     

Detection and verification of quantitative trait loci for resistance to Dothistroma needle blight in<Emphasis Type="Italic"> Pinus radiata</Emphasis>

Six related radiata pine (Pinus radiata) full-sib families were used to detect and independently verify quantitative trait loci (QTLs) for resistance to Dothistroma needle blight, caused by Dothistroma septospora. The detection families had from 26 to 30 individuals each, and had either a common maternal (31053) or paternal (31032) parent; one family (cross 4) consisted of progeny from both parents, 31053×31032. Approximately 200 additional progeny from cross 4 were clonally replicated and planted at two sites, with at least five to seven ramets of each individual per site. Marker segregation data were collected from a total of 250 RFLP and microsatellite markers, and single factor ANOVAs were conducted separately for each family and marker. A number of putative associations were observed, some across more than one family. Permutation tests were used to confirm expected probabilities of multiple associations based on chance alone. Seven markers representing at least four QTLs for resistance to Dothistroma were identified as being significant in more than one family; one of these was significant at P<0.05 in three families and highly significant at P<0.01 in a fourth. Further confirmation was obtained by testing those markers that were significant in more than one of the detection families (or highly significant in cross 4) in the clonally replicated progeny from cross 4. Four QTL positions were verified in the clonal populations, with a total percent variation accounted for of 12.5.Communicated by D.B. Neale     

Mice and Monkeys as Assay Animals for Clostridium perfringens Food Poisoning

Spores and vegetative cells of Clostridium perfringens, in combination with meat or starch paste, sterile culture filtrates, lecithinase, and phosphorylcholine, were administered to mice and rhesus monkeys in an attempt both to evaluate the animals as test agents and, if possible, to elucidate the active factors producing food-poisoning symptoms caused by this organsim. Some of the preparations were administered to the monkeys by stomach tube; others, in gelatin capsules which were treated with formaldehyde so that the release of their contents was delayed and presumably reached the intestines of the animals. Any changes in intestinal passage times and in consistency of stools of the animals were observed, and the counts of C. perfringens in the feces of the monkeys previous and subsequent to treatment were recorded. The results obtained were inconclusive. Diarrhea occurred only relatively infrequently in both species, regardless of the substance fed or the mode of administration. The changes in intestinal passage times were not great, although in the monkeys there appeared to be a slight trend toward reduction as the magnitude of the bacterial load increased. Phosphorylcholine appeared to have little, if any, effect in reducing intestinal passage time of mice or monkeys. No procedures explored in these experiments could be said to be satisfactory as a means of animal assay for food poisoning strains of C. perfringens since typical symptoms did not appear with regularity.     

Phosphorus accumulation in Proteaceae seeds: a synthesis

The family Proteaceae dominates the nutrient-poor, Mediterranean-climate floristic regions of southwestern Australia (SWA) and the Cape of South Africa. It is well-recognised that mediterranean Proteaceae have comparatively large seeds that are enriched with phosphorus (P), stored mainly as salts of phytic acid in protein globoids. Seed P can contribute up to 48% of the total aboveground P, with the fraction allocated depending on the species fire response. For SWA species, 70–80% of P allocated to fruiting structures is invested in seeds, compared with 30–75% for Cape species, with SWA species storing on average 4.7 times more P per seed at twice the concentration. When soil P is less limiting for growth, seed P reserves may be less important for seedling establishment, and hence plants there tend to produce smaller seeds with less P. For Australian Hakea and Grevillea species the translocation of P from the fruit wall to the seed occurs in the days/weeks before final fruit dry mass is reached, and accounts for 4–36% of seed P. Seed P content increases with the level of serotiny, though it decreases marginally as a fraction of the total reproductive structure. The greater occurrence of serotiny and higher seed P content within the Proteaceae in SWA supports the notion that SWA soils are more P-impoverished than those of the Cape.     

A class of human exons with predicted distant branch points revealed by analysis of AG dinucleotide exclusion zones

Background

The three consensus elements at the 3' end of human introns - the branch point sequence, the polypyrimidine tract, and the 3' splice site AG dinucleotide - are usually closely spaced within the final 40 nucleotides of the intron. However, the branch point sequence and polypyrimidine tract of a few known alternatively spliced exons lie up to 400 nucleotides upstream of the 3' splice site. The extended regions between the distant branch points (dBPs) and their 3' splice site are marked by the absence of other AG dinucleotides. In many cases alternative splicing regulatory elements are located within this region.

Results

We have applied a simple algorithm, based on AG dinucleotide exclusion zones (AGEZ), to a large data set of verified human exons. We found a substantial number of exons with large AGEZs, which represent candidate dBP exons. We verified the importance of the predicted dBPs for splicing of some of these exons. This group of exons exhibits a higher than average prevalence of observed alternative splicing, and many of the exons are in genes with some human disease association.

Conclusion

The group of identified probable dBP exons are interesting first because they are likely to be alternatively spliced. Second, they are expected to be vulnerable to mutations within the entire extended AGEZ. Disruption of splicing of such exons, for example by mutations that lead to insertion of a new AG dinucleotide between the dBP and 3' splice site, could be readily understood even though the causative mutation might be remote from the conventional locations of splice site sequences.     

Insights into the Management of Large Carnivores for Profitable Wildlife-Based Land Uses in African Savannas

Large African predators, especially lions (Panthera leo) and leopards (Panthera pardus), are financially valuable for ecotourism and trophy hunting operations on land also utilized for the production of other wildlife species for the same purpose. Predation of ungulates used for trophy hunting can create conflict with landholders and trade off thus exists between the value of lions and leopards and their impact on ungulate populations. Therefore productionist and conservation trade-offs are complexly graded and difficult to resolve. We investigated this with a risk-benefit analysis on a large private wildlife production area in Zimbabwe. Our model showed that lions result in substantial financial costs through predation on wild ungulates that may not be offset by profits from hunting them, whereas the returns from trophy hunting of leopards are projected to exceed the costs due to leopard predation. In the absence of additional income derived from photo-tourism the number of lions may need to be managed to minimize their impact. Lions drive important ecological processes, but there is a need to balance ecological and financial imperatives on wildlife ranches, community wildlife lands and other categories of multiple use land used for wildlife production. This will ensure the competitiveness of wildlife based land uses relative to alternatives. Our findings may thus be limited to conservancies, community land-use areas and commercial game ranches, which are expansive in Africa, and should not necessarily applied to areas where biodiversity conservation is the primary objective, even if hunting is allowed there.     

Species richness declines and biotic homogenisation have slowed down for NW‐European pollinators and plants

Concern about biodiversity loss has led to increased public investment in conservation. Whereas there is a widespread perception that such initiatives have been unsuccessful, there are few quantitative tests of this perception. Here, we evaluate whether rates of biodiversity change have altered in recent decades in three European countries (Great Britain, Netherlands and Belgium) for plants and flower visiting insects. We compared four 20‐year periods, comparing periods of rapid land‐use intensification and natural habitat loss (1930–1990) with a period of increased conservation investment (post‐1990). We found that extensive species richness loss and biotic homogenisation occurred before 1990, whereas these negative trends became substantially less accentuated during recent decades, being partially reversed for certain taxa (e.g. bees in Great Britain and Netherlands). These results highlight the potential to maintain or even restore current species assemblages (which despite past extinctions are still of great conservation value), at least in regions where large‐scale land‐use intensification and natural habitat loss has ceased.     

CXCR3 in T cell function

CXCR3 is a chemokine receptor that is highly expressed on effector T cells and plays an important role in T cell trafficking and function. CXCR3 is rapidly induced on naïve cells following activation and preferentially remains highly expressed on Th1-type CD4⁺ T cells and effector CD8⁺ T cells. CXCR3 is activated by three interferon-inducible ligands CXCL9 (MIG), CXCL10 (IP-10) and CXCL11 (I-TAC). Early studies demonstrated a role for CXCR3 in the trafficking of Th1 and CD8 T cells to peripheral sites of Th1-type inflammation and the establishment of a Th1 amplification loop mediated by IFNγ and the IFNγ-inducible CXCR3 ligands. More recent studies have also suggested that CXCR3 plays a role in the migration of T cells in the microenvironment of the peripheral tissue and lymphoid compartment, facilitating the interaction of T cells with antigen presenting cells leading to the generation of effector and memory cells.     

CXCR3 ligands: redundant, collaborative and antagonistic functions

CXCR3 is a chemokine receptor that is rapidly induced on na?ve T cells following activation, and preferentially remains highly expressed on type-1 helper (Th1)-type CD4(+) T cells, effector CD8(+) T cells and innate-type lymphocytes, such as natural killer (NK) and NKT cells. CXCR3 is activated by three interferon (IFN)-γ-inducible ligands CXCL9 (monokine induced by gamma-interferon), CXCL10 (interferon-induced protein-10) and CXCL11 (interferon-inducible T-cell alpha chemoattractant). Although some studies have revealed that these ligands have redundant functions in vivo, other studies have demonstrated that the three CXCR3 ligands can also collaborate and even compete with each other. Differential regulation of the three ligands at specific times in defined anatomically restricted locations in vivo likely participates in the fine control of T-cell trafficking over the course of an immune response. Among the differences in regulation, CXCL10 is induced by a variety of innate stimuli that induce IFN-α/β as well as the adaptive immune cell cytokine IFN-γ, whereas CXCL9 induction is restricted to IFN-γ. In this review, we will discuss how the balance, timing and pattern of CXCR3 ligand expression appears to regulate the generation of effector T cells in the lymphoid compartment and subsequent migration into peripheral sites of Th1-type inflammation in which the CXCR3 ligands also then regulate the interactions and migratory behavior of effector T cells in an inflamed peripheral tissue.