Thioredoxin targets of the plant chloroplast lumen and their implications for plastid function

The light‐dependent regulation of stromal enzymes by thioredoxin (Trx)‐catalysed disulphide/dithiol exchange is known as a classical mechanism for control of chloroplast metabolism. Recent proteome studies show that Trx targets are present not only in the stroma but in all chloroplast compartments, from the envelope to the thylakoid lumen. Trx‐mediated redox control appears to be a common feature of important pathways, such as the Calvin cycle, starch synthesis and tetrapyrrole biosynthesis. However, the extent of thiol‐dependent redox regulation in the thylakoid lumen has not been previously systematically explored. In this study, we addressed Trx‐linked redox control in the chloroplast lumen of Arabidopsis thaliana. Using complementary proteomics approaches, we identified 19 Trx target proteins, thus covering more than 40% of the currently known lumenal chloroplast proteome. We show that the redox state of thiols is decisive for degradation of the extrinsic PsbO1 and PsbO2 subunits of photosystem II. Moreover, disulphide reduction inhibits activity of the xanthophyll cycle enzyme violaxanthin de‐epoxidase, which participates in thermal dissipation of excess absorbed light. Our results indicate that redox‐controlled reactions in the chloroplast lumen play essential roles in the function of photosystem II and the regulation of adaptation to light intensity.     

Habitat preferences of red-listed fungi and bryophytes in woodland key habitats in southern Sweden – analyses of data from a national survey

The aim of this study was to identify habitat preferences of red-listedepiphytic and epixylic bryophyte, lichenized and non-lichenized fungi speciesinwoodland key habitats (WKHS) (areas less than 10 ha, where foreststructures indicate occurrence of red-listed species) in southern Sweden. Therelative importance of different groups of environmental factors was assessedwith partial canonical correspondence analysis techniques and across-validationapproach using data from 7196 selected WKHs. Different woody substrates (oldtrees, logs and snags) made up the most important variable group for occurrenceof red-listed species (30% unique explainable variation). Species associatedwith Fagus sylvatica and Picea abieshabitats, but also species associated with Quercus spp.andPopulus tremula habitats showed distinct habitatpreferences. The second most important variable group (16% unique explainablevariation) was geographical location. A west–east gradient was identified, andspecies concentrated to Baltic islands in the east were separated from otherspecies. This gradient, and an identified south–north gradient, probablyreflect differences in temperatures and rainfall between different regions.Among the remaining variable groups, historical land-use, ground conditions andforest stand composition were of similar importance (5–7% uniqueexplainable variation). Traditional management regimes resulting in semi-openforest habitats (leaf harvesting, forest grazing and selective cutting) wereassociated with the occurrence of many species, probably due to differences inmicroclimate between sites of different openness. Furthermore, a groundmoisturegradient extending from species associated with dry sites (mainly lichenizedfungi) to species associated with wet sites (mainly bryophytes), and a nutrientgradient from species associated with nutrient-poor sites to species occurringat nutrient-rich sites, were identified. Thus, conservation measures are neededin a broad spectrum of habitats with different substrates. Also sites withsimilar substrates, but situated in different regions (and climates), or withdifferent ground moisture and nutrient conditions are needed to cover the fullspectrum of habitat conditions suitable for different red-listed bryophytes andfungi.     

Variation in laying date in relation to spring temperature in three species of tits (Paridae) and pied flycatchers Ficedula hypoleuca in southernmost Sweden

This study documents the advancement of laying dates in three species of tits (Paridae) in southernmost Sweden during recent decades, and the absence of a similar response in the pied flycatcher Ficedula hypoleuca. It is based on several different nestbox studies; the oldest one starting in 1969. During 1969 to 2012, mean spring temperatures in the study area increased by between 0.06 and 0.08°C per year, depending on the period considered. Great tits Parus major, blue tits Cyanistes caeruleus and marsh tits Poecile palustris, which generally start egg laying between the last week of April and the first week of May, all advanced laying date at a similar rate during the study period (0.25 d yr^–1). This indicates that these species were similarly affected by increasing temperatures. When accounting for mean spring temperature variation, we still found an advancement of laying date over the study period, mostly due to such relationships among marsh and blue tits. This result could reflect ongoing microevolution favouring earlier laying, but could also be a result of other factors such as increased intra‐ or inter‐specific competition for early breeding. Pied flycatchers, which generally lay during the third week of May, did not significantly advance the date of egg laying despite that the long‐term trend in the increase in ambient temperature during the 30‐d period preceding the start of egg laying was similar for pied flycatchers compared to the tit species.     

Effects of soil resources on expression of a sexual conflict over timing of stigma receptivity in a mixed‐mating plant

While environmental factors strongly influence plant growth and reproduction, less is known about environmental effects on sexual selection and sexual conflict. In this study on mixed‐mating Collinsia heterophylla we investigated whether soil resource environment affected traits associated with sexual conflict. In C. heterophylla a sexual conflict over timing of stigma receptivity occurs. Early stigma receptivity benefits pollen parents by securing paternity while late stigma receptivity benefits female fitness in terms of increased seed production. We performed hand‐pollinations combining recipients and donors grown either in high or low resource environments and asked whether these treatments influenced sexual conflict traits – recipient‐ and donor‐based influence on timing of stigma receptivity – and conflict costs related to reduced early seed production. We also asked whether resource environment affected eight traits related to general fitness and mating system. Sexual conflict‐associated traits – timing of stigma receptivity and seed production – were generally unaffected by resource environment. While no universal effect of resources was detected, we did observe donor‐specific responses to environment, suggesting that environment can nonetheless contribute to variation in timing of stigma receptivity. Recipients grown under low resources showed pronounced differences among donors for number of seeds per capsule, indicating that recipients favour some donors over others under resource‐low conditions. Moreover, high resources increased number of flowers but reduced pollen germination rate, while other traits were unaffected, indicating variation in the response to resource environment for fitness‐ and mating system‐traits. Our results suggest that even though soil resource environment had a low impact on the sexual conflict traits and related costs in C. heterophylla, it generated variability in pollen donor‐influence on this trait and in recipient sorting among donors. Thus, it is possible that both sexual conflict and sexual selection is affected by environmental factors not only in animals but also in plants.     

To boldly go: individual differences in boldness influence migratory tendency

Partial migration, whereby only a fraction of the population migrates, is thought to be the most common type of migration in the animal kingdom, and can have important ecological and evolutionary consequences. Despite this, the factors that influence which individuals migrate and which remain resident are poorly understood. Recent work has shown that consistent individual differences in personality traits in animals can be ecologically important, but field studies integrating personality traits with migratory behaviour are extremely rare. In this study, we investigate the influence of individual boldness, an important personality trait, upon the migratory propensity of roach, a freshwater fish, over two consecutive migration seasons. We assay and individually tag 460 roach and show that boldness influences migratory propensity, with bold individuals being more likely to migrate than shy fish. Our data suggest that an extremely widespread personality trait in animals can have significant ecological consequences via influencing individual-level migratory behaviour.     

Morph‐specific selection on floral traits in a polymorphic plant

Correlations between phenotypic traits are common in many organisms, but the relative importance of nonadaptive mechanisms and selection for the evolution and maintenance of such correlations are poorly understood. In polymorphic species, morphs may evolve quantitative differences in additional characters as a result of morph‐specific selection. The perennial rosette herb Primula farinosa is polymorphic for scape length. The short‐scaped morph is less damaged by grazers and seed predators but is more strongly pollen limited than the long‐scaped morph. We examined whether morph‐specific differences in biotic interactions are associated with differences in selection on two other traits affecting floral display (number of flowers and petal size) and on one trait likely to affect pollination efficiency (corolla tube width) in three P. farinosa populations. Differences in selection between morphs were detected in one population. In this population, selection for more flowers and larger petals was stronger in the short‐scaped than in the long‐scaped morph, and although there was selection for narrower corolla tubes in the short‐scaped morph, no statistically significant selection on corolla tube width could be detected in the long‐scaped morph. In the study populations, the short‐scaped morph produced more and larger flowers and wider corolla tubes. Current morph‐specific selection was thus only partly consistent with trait differences between morphs. The results provide evidence of morph‐specific selection on traits associated with floral display and pollination efficiency, respectively.     

Specificity in Arabidopsis thaliana recruitment of root fungal communities from soil and rhizosphere

Biotic and abiotic conditions in soil pose major constraints on growth and reproductive success of plants. Fungi are important agents in plant soil interactions but the belowground mycobiota associated with plants remains poorly understood. We grew one genotype each from Sweden and Italy of the widely-studied plant model Arabidopsis thaliana. Plants were grown under controlled conditions in organic topsoil local to the Swedish genotype, and harvested after ten weeks. Total DNA was extracted from three belowground compartments: endosphere (sonicated roots), rhizosphere and bulk soil, and fungal communities were characterized from each by amplification and sequencing of the fungal barcode region ITS2. Fungal species diversity was found to decrease from bulk soil to rhizosphere to endosphere. A significant effect of plant genotype on fungal community composition was detected only in the endosphere compartment. Despite A. thaliana being a non-mycorrhizal plant, it hosts a number of known mycorrhiza fungi in its endosphere compartment, which is also colonized by endophytic, pathogenic and saprotrophic fungi. Species in the Archaeorhizomycetes were most abundant in rhizosphere samples suggesting an adaptation to environments with high nutrient turnover for some of these species. We conclude that A. thaliana endosphere fungal communities represent a selected subset of fungi recruited from soil and that plant genotype has small but significant quantitative and qualitative effects on these communities.     

Zinc, Copper, and Selenium Tissue Levels and Their Relation to Subcutaneous Abscess, Minor Surgery, and Wound Healing in Humans

Trace element involvement in wounds left to heal by secondary intention needs clarification. We have previously reported faster healing of wounds following acute surgery compared with elective excision of pilonidal sinus disease. The effect of topical zinc on the closure of the excisional wounds was mediocre compared with placebo. In contrast, parenteral zinc, copper, and selenium combined appear effective for wound healing in humans. We have investigated zinc, copper, and selenium with respect to (a) impact of acute versus chronic pilonidal sinus and (b) regional concentrations within granulating wounds treated topically with placebo or zinc in 42 (33 males) pilonidal disease patients. Baseline serum and skin concentrations of copper correlated (r _S?=?0.351, p?=?0.033, n?=?37), but not of zinc or selenium. Patients with abscesses had elevated serum C-reactive protein (CRP) and copper levels (+29 %; p?<?0.001) compared with the elective patients consistent with the strong correlation between serum copper and CRP (r _S?=?0.715, p?<?0.0005, n?=?41). Seven days after elective surgery, serum CRP and copper levels were elevated (p?=?0.010) versus preoperative values. The copper concentration in wound edges was higher than in periwound skin (p?<?0.0005) and wound base (p?=?0.010). Selenium levels were increased in wound edge compared to wound base (p?=?0.003). Topical zinc oxide treatment doubled (p?<?0.050) zinc concentrations in the three tissue localizations without concomitant significant changes of copper or selenium levels. In conclusion, copper and selenium are mobilized to injured sites possibly to enhance host defense and early wound healing mechanisms that are complementary to the necessity of zinc for matrix metalloproteinase activity.     

Pollen Tube Cytoskeleton: Structure and Function

   apd: 3 July 2001     

Endocytotic uptake of cationized ferritin tracer into glomus cells dissociated from the adult rat carotid body

Summary Glomus cells from carotid bodies of adult rats dissociated by means of collagenase or collagenase + trypsin were used to study by electron microscopy the endocytotic uptake of cationized ferritin (CF) tracer into subcellular compartments. The glomus cells were incubated with the tracer (1) in a basic salt medium (BM), or (2) in the BM into which calcium ionophore A23187 had been added, or (3) in a potassium-rich medium.Incubation of the cells in BM containing CF for 30 min resulted in attachment of the tracer to the cell membrane and uptake of a few solitary tracer particles into small vesicles and multivesicular bodies. No uptake into the cisternae of the Golgi apparatus was observed. Further incubation in BM containing CF for another 30 min resulted in increased uptake of the tracer into small vesicles and multivesicular bodies. A similar pattern of uptake was observed when the dissociated glomus cells were first preincubated in BM with CF for 30 min and then incubated for 1 min or 30 min in the BM solution containing both the ionophore and CF. Upon such incubation, CF particles were seen to penetrate into coated pits and sites of exocytosis at the cell surface. When the 30-min preincubation in BM was followed by incubation in a CF-containing potassium-rich medium for 15–30 min, uptake into vesicles, small lysosomes and occasionally also into profiles of the smooth endoplasmic reticulum was seen. Endocytotic mechanisms of the glomus cells are outlined.