Plasticity in ploidy underlies plant fitness compensation to herbivore damage

How plants mitigate damage by animal herbivores is a fundamental ecological and evolutionary question of plant–animal interactions. Some plants can increase their fitness when damaged in a phenomenon termed ‘overcompensation’. Despite overcompensation being observed in a variety of plant species, its mechanistic basis remains elusive. Recent research has shown that the Arabidopsis thaliana genotype Columbia‐4 employs endoreduplication, the replication of the genome without mitosis, following damage and that it overcompensates for seed yield. The related genotype Landsberg erecta, in contrast, does not increase its endoreduplication following damage and suffers reduced seed yield. While these results suggest that a plant's ability to plastically increase its ploidy during regrowth may promote its mitigation of damage, no studies have explicitly linked the endoreduplication genetic pathway to the regrowth and fitness of damaged plants. By comparing fitness and ploidy between undamaged and damaged plants of Columbia‐4, Landsberg erecta and their offspring, we provide evidence that endoreduplication is directly involved in compensatory performance. We then overexpressed an endoreduplication regulator and compared this mutant's endoreduplication and compensation with its background genotype Columbia‐0, an undercompensator. Enhancing Columbia‐0's ability to endoreduplicate during regrowth led to the complete mitigation of the otherwise detrimental effects of damage on its fitness. These results suggest that the ability of these plants to increase their ploidy via endoreduplication directly impacts their abilities to compensate for damage, providing a novel mechanism by which some plants can mitigate or even benefit from apical damage with potential across the wide range of plant taxa that endoreduplicate.     

Lung alveolar integrity is compromised by telomere shortening in telomerase-null mice

Shortened telomeres are a normal consequence of cell division. However, telomere shortening past a critical point results in cellular senescence and death. To determine the effect of telomere shortening on lung, four generations of B6.Cg-Terc(tm1Rdp) mice, null for the terc component of telomerase, the holoenzyme that maintains telomeres, were bred and analyzed. Generational inbreeding of terc-/- mice caused sequential shortening of telomeres. Lung histology from the generation with the shortest telomeres (terc-/- F4) showed alveolar wall thinning and increased alveolar size. Morphometric analysis confirmed a significant increase in mean linear intercept (MLI). terc-/- F4 lung showed normal elastin deposition but had significantly decreased collagen content. Both airway and alveolar epithelial type 1 cells (AEC1) appeared normal by immunohistochemistry, and the percentage of alveolar epithelial type 2 cells (AEC2) per total cell number was similar to wild type. However, because of a decrease in distal lung cellularity, the absolute number of AEC2 in terc-/- F4 lung was significantly reduced. In contrast to wild type, terc-/- F4 distal lung epithelium from normoxia-maintained mice exhibited DNA damage by terminal deoxynucleotidyltransferase (TdT)-mediated dUTP nick end labeling (TUNEL) and 8-oxoguanine immunohistochemistry. Western blotting of freshly isolated AEC2 lysates for stress signaling kinases confirmed that the stress-activated protein kinase (SAPK)/c-Jun NH(2)-terminal kinase (JNK) stress response pathway is stimulated in telomerase-null AEC2 even under normoxic conditions. Expression of downstream apoptotic/stress markers, including caspase-3, caspase-6, Bax, and HSP-25, was also observed in telomerase-null, but not wild-type, AEC2. TUNEL analysis of freshly isolated normoxic AEC2 showed that DNA strand breaks, essentially absent in wild-type cells, increased with each successive terc-/- generation and correlated strongly with telomere length (R(2) = 0.9631). Thus lung alveolar integrity, particularly in the distal epithelial compartment, depends on proper telomere maintenance.     

Dynamic changes in microbial community structure and function in phenol-degrading microcosms inoculated with cells from a contaminated aquifer

Contamination of aquifers by organic pollutants threatens groundwater supplies and the environment. In situ biodegradation of organic pollutants by microbial communities is important for the remediation of contaminated sites, but our understanding of the relationship between microbial development and pollutant biodegradation is poor. A particular challenge is understanding the in situ status of microorganisms attached to solid surfaces, but not accessible via conventional sampling of groundwater. We have developed novel flow-through microcosms and examined dynamic changes in microbial community structure and function in a phenol-degrading system. Inoculation of these microcosms with a complex microbial community from a plume in a phenol-contaminated aquifer led to the initial establishment of a population dominated by a few species, most attached to the solid substratum. Initially, phenol biodegradation was incomplete, but as the microbial community structure became more complex, phenol biodegradation was more extensive and complete. These results were replicated between independent microcosms, indicating a deterministic succession of species. This work demonstrates the importance of examining community dynamics when assessing the potential for microbial biodegradation of organic pollutants. It provides a novel system in which such measurements can be made readily and reproducibly to study the temporal development and spatial succession of microbial communities during biodegradation of organic pollutants at interfaces within such environments.     

Imaging photosynthesis in wounded leaves of Arabidopsis thaliana

Chlorophyll fluorescence imaging provides a non-invasive and non-destructive means with which to measure photosynthesis. This technique has been used, in combination with 14CO2 feeding, to study the spatial and temporal changes in source-sink relationships which occur in mechanically wounded leaves of Arabidopsis thaliana. Twenty-four hours after wounding, cells proximal to the wound margin showed a rapid induction of PhiII upon illumination (a measure of the efficiency of photosystem II photochemistry) whilst cells more distal to the wound margin exhibited a much slower induction of PhiII and a large, transient increase in NPQ (a measure of the rate constant for non-photochemical energy dissipation within the light-harvesting antenna). These results are indicative of an increase in sink strength in the vicinity of the wound and this was confirmed by the retention of 14C photosynthate in this region. It has been hypothesized that wound-induced cell wall (apoplastic) invertase (cwINV) activity plays a central role in generating localized increases in sink strength in stressed plant tissue and that hexose sugars generated by the sucrolytic activity of cwINV may act as a signal regulating gene expression. Enzyme activity measurements, quantitative RT-PCR, and T-DNA insertional mutagenesis have been used to determine that expression of AtcwINV1 is responsible for all induced cwINV activity in mechanically wounded leaves. Whilst inactivation of this gene abolished wound-induced cwINV activity, it did not affect localized alterations in source-sink relationships of wounded leaves or wound-regulated gene expression. The signals that may regulate source-sink relationships and signalling in wounded leaves are discussed.     

New Rice for Africa (NERICA) cultivars exhibit different levels of post-attachment resistance against the parasitic weeds Striga hermonthica and Striga asiatica

Striga hermonthica and S. asiatica are root parasitic weeds that infect the major cereal crops of sub-Saharan Africa causing severe losses in yield. The interspecific upland NEw RICe for Africa (NERICA) cultivars are popular amongst subsistence farmers, but little is known about their post-attachment resistance against Striga. Here, we evaluate the post-attachment resistance levels of the NERICA cultivars and their parents against ecotypes of S. hermonthica and S.asiatica, characterize the phenotype of the resistance mechanisms and determine the effect of Striga on host biomass. Some NERICA cultivars showed good broad-spectrum resistance against several Striga ecotypes, whereas others showed intermediate resistance or were very susceptible. The phenotype of a resistant interaction was often characterized by an inability of the parasite to penetrate the endodermis. Moreover, some parasites formed only a few connections to the host xylem, grew slowly and remained small. The most resistant NERICA cultivars were least damaged by Striga, although even a small number of parasites caused a reduction in above-ground host biomass. The elucidation of the molecular genetic basis of the resistance mechanisms and tolerance would allow the development of cultivars with multiple, durable resistance for use in farmers' fields.     

Survival of Campylobacter spp. in bovine faeces on pasture

Aims:  To determine the survival on pasture of Campylobacter spp. naturally present in bovine faeces and compare this with a previously published study using laboratory-cultured Campylobacter spp.
Methods and Results:  Ten freshly collected cow pats were deposited on pasture during summer, and Campylobacter spp. were enumerated by enrichment broth culture. The counts in three pats were below detection limits. Counts of Campylobacter spp. in the other seven pats fell below detection limits within 14 days. The geometric means of the counts up to 7 days produced a T ₉₀ of 2·2 days. Characterization of Campylobacter spp. by PCR and pulsed field gel electrophoresis indicated the presence of at least six genotypes of Campylobacter jejuni , Campylobacter coli and Campylobacter lari .
Conclusions:  Campylobacter spp. naturally present in cow faeces exhibited a similar survival rate to that previously determined using laboratory-cultured strains. The highly variable counts of naturally occurring Campylobacter spp., and the predominance of lower counts, also support the earlier decision to use laboratory-cultured strains in survival experiments.
Significance and Impact of the Study:  This study reaffirms the short survival of Campylobacter spp. in cow faeces deposited on pasture. This information will be incorporated into a 'reservoir model' for Campylobacter spp. in cow pats on New Zealand pastures.     

Factors associated with bovine neonatal pancytopenia (BNP) in calves: a case-control study

Bovine neonatal pancytopenia (BNP; previously known as idiopathic haemorrhagic diathesis and commonly known as bleeding calf syndrome) is a novel haemorrhagic disease of young calves which has emerged in a number of European countries during recent years. Data were retrospectively collected during June to November 2010 for 56 case calves diagnosed with BNP between 17 March and 7 June of the same year. These were compared with 58 control calves randomly recruited from herds with no history of BNP. Multivariable logistic regression analysis showed that increased odds of a calf being a BNP case were associated with its dam having received PregSure? BVD (Pfizer Animal Health) vaccination prior to the birth of the calf (odds ratio (OR) 40.78, p<0.001) and its herd of origin being located in Scotland (OR 9.71, p?=?0.006). Decreased odds of a calf being a BNP case were associated with the calf having been kept outside (OR 0.11, p?=?0.006). The longer that a cattle herd had been established on the farm was also associated with decreased odds of a calf in that herd being a BNP case (OR 0.97, p?=?0.011).     

Mitochondrial DNA diversity of <Emphasis Type="Italic">Cleruchoides noackae</Emphasis> (Hymenoptera: Mymaridae): a potential biological control agent for <Emphasis Type="Italic">Thaumastocoris peregrinus</Emphasis> (Hemiptera: Thaumastocoridae)

Thaumastocoris peregrinus Carpintero and Dellapé (Hemiptera: Thaumastocoridae) is a native Australian Eucalyptus sap-feeding insect that has become invasive and seriously damaging to commercially grown Eucalyptus in the Southern Hemisphere. Cleruchoides noackae Lin and Huber (Hymenoptera: Mymaridae) was recently discovered as an egg parasitoid of the Thaumastocoridae in Australia. Mitochondrial DNA (mtDNA; cytochrome c oxidase subunit I, COI) sequence diversity amongst 104 individuals from these native C. noackae populations revealed 24 sequence haplotypes. The COI haplotypes of individuals collected from the Sydney and Southeast Queensland clustered in distinct groups, indicating limited spread of the insect between the regions. Individuals collected from Perth in Western Australia were represented by four COI haplotypes. Although this population is geographically more isolated from other populations, two COI haplotypes were identical to haplotypes found in the Sydney region. The results suggest that C. noackae has recently been introduced into Perth, possibly from the Sydney area. The high mtDNA diversity and limited spread that is suggested for C. noackae is in contrast to the lack of geographic associated mtDNA diversity and extensive spread of T. peregrinus. If implemented as a biological control agent, this factor will need to be considered in collecting and releasing C. noackae.