Pollinator sharing in dioecious figs (Ficus: Moraceae)

As one of the most specialized pollination syndromes, the fig (Ficus)–fig wasp (Agaonidae) mutualism can shed light on how pollinator behaviour and specificity affect plant diversification through processes such as reproductive isolation and hybridization. Pollinator sharing among species has important implications for Ficus species delimitation and the evolutionary history of the mutualism. Although agaonid wasp pollinators are known to visit more than one host species in monoecious figs, pollinator sharing has yet to be documented in dioecious figs. The present study investigated the frequency of pollinator sharing among sympatric, closely‐related dioecious figs in Ficus sections Sycocarpus and Sycidium. Molecular and morphological species identification established the associations between pollinating agaonid wasp species and host fig species. Cytochrome oxidase I was sequenced from 372 Ceratosolen pollinators of Ficus section Sycocarpus and 210 Kradibia pollinators of Ficus section Sycidium. The association between fig species and morphologically distinct clades of pollinator haplotypes was predominantly one‐to‐one. In Ceratosolen, six of 372 pollinators (1.5%) visited fig species other than the predominant host. No pollinator sharing was detected between the two Sycidium host species, although a rare hybrid shared Kradibia pollinators with both parental species. These findings point to low rates of pollinator sharing among closely‐related dioecious fig species in sympatry, and perhaps lower rates than among monoecious figs. Such rare events could be evolutionarily important as mechanisms for gene flow among fig species. Differences in rates of pollinator sharing among fig lineages might explain the conflicting phylogenetic patterns inferred among monoecious figs, dioecious figs, and their respective pollinators. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 103 , 546–558.     

Bryophytes attenuate anthropogenic nitrogen inputs in boreal forests

Productivity in boreal ecosystems is primarily limited by available soil nitrogen (N), and there is substantial interest in understanding whether deposition of anthropogenically derived reactive nitrogen (N_r) results in greater N availability to woody vegetation, which could result in greater carbon (C) sequestration. One factor that may limit the acquisition of N_r by woody plants is the presence of bryophytes, which are a significant C and N pool, and a location where associative cyanobacterial N‐fixation occurs. Using a replicated stand‐scale N‐addition experiment (five levels: 0, 3, 6, 12, and 50 kg N ha^?1 yr^?1; n=6) in the boreal zone of northern Sweden, we tested the hypothesis that sequestration of N_r into bryophyte tissues, and downregulation of N‐fixation would attenuate N_r inputs, and thereby limit anthropogenic N_r acquisition by woody plants. Our data showed that N‐fixation per unit moss mass and per unit area sharply decreased with increasing N addition. Additionally, the tissue N concentrations of Pleuorzium schreberi increased and its biomass decreased with increasing N addition. This response to increasing N addition caused the P. schreberi N pool to be stable at all but the highest N addition rate, where it significantly decreased. The combined effects of changed N‐fixation and P. schreberi biomass N accounted for 56.7% of cumulative N_r additions at the lowest N_r addition rate, but only a minor fraction for all other treatments. This ‘bryophyte effect’ can in part explain why soil inorganic N availability and acquisition by woody plants (indicated by their δ¹⁵N signatures) remained unchanged up to N addition rates of 12 kg ha^?1 yr^?1 or greater. Finally, we demonstrate that approximately 71.8% of the boreal forest experiences N_r deposition rates at or below 3 kg ha^?1 yr^?1, suggesting that bryophytes likely limit woody plant acquisition of ambient anthropogenic N_r inputs throughout a majority of the boreal forest.     

A class III peroxidase specifically expressed in pathogen-attacked barley epidermis contributes to basal resistance

Higher plants possess large multigene families encoding secreted class III peroxidase (Prx) proteins. In barley, two Prx cDNAs encoding HvPrx07 and HvPrx08 have been isolated and characterized to some extent with respect to a resistance-mediating function upon attack by the powdery-mildew fungus Blumeria graminis f.sp. hordei ( Bgh ). Here we present evidence for the tissue-specific accumulation of a new Prx mRNA, HvPrx40 , in Bgh -attacked epidermis of barley ( Hordeum vulgare ). The encoded protein is predicted to be secreted into the apoplastic space of epidermal cells due to the absence of a C-terminal extension, which distinguishes it from other Prx proteins reported to accumulate in leaf epidermis. Transient overexpression of HvPrx40 enhanced the resistance of wheat ( Triticum aestivum ) and barley against Blumeria graminis f.sp. tritici (wheat powdery mildew) and Bgh , respectively. These findings were complemented by transient-induced gene silencing showing hypersusceptibility of barley leaf epidermal cells to Bgh . The local accumulation of oxidized 3,3-diaminobenzidine that reflects H₂O₂ production at sites of attempted fungal penetration was not reduced in HvPrx40 -silenced cells, suggesting a role of this peroxidase other than the production of reactive oxygen species.     

Melanins in IGR 1 Melanoma Cells

Information on the composition of melanins is obtained by analysis both of 4-amino-3-hydroxyphenylalanine (AHP) after hydriodic acid degradation and of pyrrole-2,3,5-tricarboxylic acid (PTCA) after potassium permanganate oxidation. Analysis of thiazole-4,5-dicarboxylic acid (TDCA) and pyrrole-2,3-dicarboxylic acid (PDCA) after permanganate oxidation, provides additional information on the composition, TDCA on pheomelanin residues, and PDCA on indolic residues without carboxy groups. Using model melanins formed from dopa and cysteinyldopa in different proportions, we found the TDCA/(PTCA+PDCA) ratio to yield a reliable estimate of the relative proportions of pheomelanin and eumelanin. The PDCA/PTCA ratio reflects the relationship between indole residues with and without carboxy groups. We have analyzed degradation products from cultures of IGR 1, an extensively studied melanoma cell line. Cell cultures were harvested after 2, 4, and 7 days. Culture media were changed after 2 days in all series, and also after 4 days in one series harvested at 7 days. Cells without medium change had seven times the amount of melanin found in cultures with medium change. The PDCA/PTCA ratio decreased with increasing amounts of melanin. With increased melanization, eumelanin is increased relatively more than pheomelanin. The cell content of 5-S-cysteinyldopa (5-S-CD) was similar in all cultures, while 6-hydroxy-5-methoxyindole-2-carboxylic acid (6H5MICA), a eumelanin precursor metabolite, was found in increased amounts of media of heavily pigmented cultures.     

Subsidy‐stress and multiple‐stressor effects along gradients of deposited fine sediment and dissolved nutrients in a regional set of streams and rivers

1. Stream managers need to understand relationships between multiple stressors and ecological responses. We examined responses of benthic invertebrates and algae along two land‐use‐related stressor gradients of concern in running waters. Our correlative study of the consequences of augmented deposited fine sediment and nutrient concentrations was conducted in a regional set of streams and rivers monitored by a water management authority in New Zealand and incorporated a wide range of catchment geologies and stream orders. 2. We used multiple linear regression analysis and an information‐theoretic approach to select the best predictive models for our biological response variables by testing multiple competing hypotheses that include nonlinear subsidy‐stress relationships and interactive effects between the two stressors. 3. Patterns consistent with a subsidy‐stress response to increasing dissolved inorganic nitrogen concentration were found for the relative abundances of the common invertebrate genera Pycnocentrodes and Deleatidium and for the relative abundance of total individuals in the EPT orders (Ephemeroptera, Plecoptera, Trichoptera). 4. Fine sediment seemed the more pervasive stressor, apparently counteracting and overwhelming any initial subsidy effect of increased nutrients, and accounting for more of the variance in biological response variables. Relationships with high nutrient concentrations were weaker and modelled with less certainty, probably reflecting the indirect modes of action of nutrients compared to those underlying sediment effects. Nevertheless, in several cases, the models indicated that nutrients interacted synergistically with fine sediment, lending further weight to the conclusion that managers need to address both stressors to achieve the best outcomes.     

Neuromelanin and its Possible Protective and Destructive Properties

The function of neuromelanin is not known, but some properties of the pigment suggest a protective action. Its unique ability to accumulate and retain several compounds, such as various amines and a number of metals, may protect the pigment-containing neurons from high exposure to harmful substances. This possible mechanism of protection may however in certain instances be of a double-edged nature, as accumulation of neurotoxic agents with a high melanin affinity may cause toxic concentrations in the neuro-melanin-containing cells. MPTP (l-methyl-4-phenyl-l,2,3,6-tetrahydropyridine) seems to be such a compound, as it has been found to preferentially destroy neuromelanin-containing cells. The degree of MPTP neurotoxicity seems to be related to the amount of neuromelanin present in the particular species. It is possible that also manganese, which is known to cause an extrapyramidal disorder resembling Parkinson's disease, causes injury to neuromelanin-bearing neurons due to its melanin affinity. This mechanism may be involved in other forms of chemically induced Parkin-sonism and possibly also in idiopathic Parkinson's disease, although the offending agent remains to be discovered.