Direct acquisition of organic N by white clover even in the presence of inorganic N

Aim

This study was conducted to answer the question of whether clover can absorb asparagine in the presence and absence of inorganic nitrogen, as well as to determine the resulting concentration of post-uptake compounds closely involved in asparagine metabolism.

Methods

Clover was grown at two asparagine concentrations (10 μM and 1 mM) supplied in both the absence and presence of ammonium nitrate. Using dual-labeled ¹³C¹⁵N-asparagine, the uptake rate was analyzed via bulk ¹⁵N and ¹³C excess and the detection of intact ¹³C¹⁵N-asparagine in white clover.

Results

The results from the two methods indicated greater utilization of ¹³C¹⁵N-asparagine in the 10 μM treatment than in the 1 mM treatment. The ¹³C¹⁵N-asparagine uptake rate was higher when ¹³C¹⁵N-asparagine was provided alone than when it was supplemented with inorganic nitrogen. Up to nine times lower uptake rates were obtained when intact ¹³C¹⁵N-asparagine was measured than when bulk ¹⁵N and ¹³C excess were analyzed. The labeled amino acids that are closely related to ¹³C¹⁵N-asparagine metabolism (aspartic acid, glutamic acid and glutamine) were detected in clover roots and shoots.

Conclusions

Using two different methods, white clover’s potential to absorb intact asparagine, even in the presence of inorganic nitrogen, was confirmed. The dual-methodology approach employed in this study demonstrates how the post-uptake metabolism can affect quantification of amino acid uptake.

     

Phylogeography of Scots pine in Europe and Asia based on mtDNA polymorphisms

We analyzed mitochondrial DNA polymorphisms to search for evidence of the genetic structure and patterns of admixture in 124 populations (N = 1407 trees) across the distribution of Scots pine in Europe and Asia. The markers revealed only a weak population structure in Central and Eastern Europe and suggested postglacial expansion to middle and northern latitudes from multiple sources. Major mitotype variants include the remnants of Scots pine at the north-western extreme of the distribution in the Scottish Highlands; two main variants (western and central European) that contributed to the contemporary populations in Norway and Sweden; the central-eastern European variant present in the Balkan region, Finland, and Russian Karelia; and a separate one common to most eastern European parts of Russia and western Siberia. We also observe signatures of a distinct refugium located in the northern parts of the Black Sea basin that contributed to the patterns of genetic variation observed in several populations in the Balkans, Ukraine, and western Russia. Some common haplotypes of putative ancient origin were shared among distant populations from Europe and Asia, including the most southern refugial stands that did not participate in postglacial recolonization of northern latitudes. The study indicates different genetic lineages of the species in Europe and provides a set of genetic markers for its finer-scale population history and divergence inference.     

Phototropin Mediated Relocation of Myosins in Arabidopsis thaliana

Background

The mechanism of the light-dependent movements of chloroplasts is based on actin and myosin but its details are largely unknown. The movements are activated by blue light in terrestrial angiosperms. The aim of the present study was to determine the role of myosin associated with the chloroplast surface in the light-induced chloroplast responses in Arabidopsis thaliana. The localization of myosins was investigated under blue light intensities generating avoidance and accumulation responses of chloroplasts. The localization was compared in wild type plants and in phot2 mutant lacking the avoidance response.

Results

Wild type and phot2 mutant plants were irradiated with strong (36 µEm⁻²s⁻¹) and/or weak (0.8 µEm⁻²s⁻¹) blue light. The leaf tissue was immunolabeled with antimyosin antibodies. Different arrangements of myosins were observed in the mesophyll depending on the fluence rate in wild type plants. In tissue irradiated with weak blue light myosins were associated with chloroplast envelopes. In contrast, in tissue irradiated with strong blue light chloroplasts were almost myosin-free. The effect did not occur in red light and in the phot2 mutant.

Conclusions

Myosin displacement is blue light specific, i.e., it is associated with the activation of a specific blue-light photoreceptor. We suggest that the reorganization of myosins is essential for chloroplast movement. Myosins appear to be the final step of the signal transduction pathway starting with phototropin2 and leading to chloroplast movements.Key Words: Arabidopsis, blue light, chloroplast movements, myosins, phototropins     

LSD1‐, EDS1‐ and PAD4‐dependent conditional correlation among salicylic acid,hydrogen peroxide,water use efficiency and seed yield in Arabidopsis thaliana

In Arabidopsis thaliana, LESION SIMULATING DISEASE 1 (LSD1), ENHANCED DISEASE SUSCEPTIBILITY 1 (EDS1) and PHYTOALEXIN DEFICIENT 4 (PAD4) proteins are regulators of cell death (CD) in response to abiotic and biotic stresses. Hormones, such as salicylic acid (SA), and reactive oxygen species, such as hydrogen peroxide (H₂O₂), are key signaling molecules involved in plant CD. The proposed mathematical models presented in this study suggest that LSD1, EDS1 and PAD4 together with SA and H₂O₂ are involved in the control of plant water use efficiency (WUE), vegetative growth and generative development. The analysis of Arabidopsis wild‐type and single mutants lsd1, eds1, and pad4, as well as double mutants eds1/lsd1 and pad4/lsd1, demonstrated the strong conditional correlation between SA/H₂O₂ and WUE that is dependent on LSD1, EDS1 and PAD4 proteins. Moreover, we found a strong correlation between the SA/H₂O₂ homeostasis of 4‐week‐old Arabidopsis leaves and a total seed yield of 9‐week‐old plants. Altogether, our results prove that SA and H₂O₂ are conditionally regulated by LSD1/EDS/PAD4 to govern WUE, biomass accumulation and seed yield. Conditional correlation and the proposed models presented in this study can be used as the starting points in the creation of a plant breeding algorithm that would allow to estimate the seed yield at the initial stage of plant growth, based on WUE, SA and H₂O₂ content.     

Actin cytoskeleton in Arabidopsis thaliana under blue and red light

BACKGROUND INFORMATION: Actin cytoskeleton is the basis of chloroplast-orientation movements. These movements are activated by blue light in the leaves of terrestrial angiosperms. Red light has been shown to affect the spatial reorganization of F-actin in water plants, where chloroplast movements are closely connected with cytoplasmic streaming. The aim of the present study was to determine whether blue light, which triggers characteristic responses of chloroplasts, i.e. avoidance and accumulation, also influences F-actin organization in the mesophyll cells of Arabidopsis thaliana. Actin filaments in fixed mesophyll tissue were labelled with Alexa Fluor 488-conjugated phalloidin. The configuration of actin filaments, expressed as a form factor (4 pi x area/perimeter(2)), was determined for all actin formations which were measured in fluorescence confocal images. RESULTS: In the present study, we compare form-factor distributions and the median form factors for strong and weak, blue- and red-irradiated tissues. Spatial organization of the F-actin network did not undergo any changes which could be attributed specifically to blue light. Actin patterns were similar in blue-irradiated wild-type plants and phot2 (phototropin 2) mutants which lack the avoidance response of chloroplasts. However, significant differences in the shape and distribution of F-actin formations were observed between mesophyll cells of phot2 mutants irradiated with strong and weak red light. These differences were absent in wild-type leaves. CONCLUSIONS: Actin does not appear to be the main target for the blue-light chloroplast-orientation signal. The modes of actin involvement in chloroplast translocations are different in water and terrestrial angiosperms. The results suggest that co-operation occurs between blue- and red-light photoreceptors in the control of the actin cytoskeleton architecture in Arabidopsis.     

Study on the Materials Formed by Self‐Assembling Hydrophobic,Aromatic Peptides Dedicated to Be Used for Regenerative Medicine

The aims of this study were to identify the short aromatic peptides which are able to form highly ordered amyloid‐like structures in self‐assembling processes, to test the influence of length of hydrophobic peptides on tendency to aggregation, and to check if aggregated peptides fulfill requirements expected for materials useful for scaffolding. All tested hydrophobic peptides were prepared on solid phase by using DMT/NMM/TsO^? as a coupling reagent. The progress of aggregation was studied by set of independent tests. All aggregated peptides were found stable under in vitro conditions. All fibrous material formed by self‐assembling of peptides does not show any cytotoxic effects on L929 fibroblast cells. Peptides containing tyrosine and tryptophan residues even effectively accelerated the proliferation and stimulated the activity of L929 fibroblasts.     

Mannose,but not glucose or sucrose,disturbs actin cytoskeleton in <Emphasis Type="Italic">Arabidopsis thaliana</Emphasis> leaves

A dynamic cytoskeleton able to recognize and respond to both abiotic and biotic stimuli is necessary for the proper functioning of a living cell. The cytoskeleton is involved in cell growth and division, maintenance of cell shape, cytoplasmic streaming, and organelle movements. Numerous studies have focused on the relationships between sugar metabolism, sugar signaling, and the cytoskeleton in yeast and animal cells. Data on such connections in plants are scarce. In the present study we investigated the effects of exogenously delivered sugars on the plant actin cytoskeleton. Detached Arabidopsis thaliana leaves were incubated with sugars for 2 days and the cytoskeleton was visualized using fluorescent-labeled phalloidin. Glucose and sucrose did not influence the pattern of the actin cytoskeleton. In contrast, mannose caused the disappearance of filamentous structures and generated actin foci. The symptoms started to be visible after 24 h of the exposure to mannose. The effect did not occur in Nicotiana tabacum mesophyll cells. This insensitivity was probably due to the presence of phosphomannose isomerase in tobacco cells. Mannose is commonly used as a selection marker for the transformation of plants lacking the enzymes responsible for the metabolism of mannose-6-phosphate. Exposure to this hexose has been linked with DNA fragmentation and a release of cytochrome c from mitochondria. Both responses are treated as features of programmed cell death. However, in our experiments no DNA laddering was observed in mannose-treated Arabidopsis leaves.     

The expression patterns of heat shock genes and proteins and their role during vertebrate's development

Highly evolutionary conserved heat shock proteins (HSPs) act as molecular chaperones in regulation of cellular homeostasis and promoting survival. Generally they are induced by a variety of stressors whose effect could be disastrous on the organism, but they are also widely constitutively expressed in the absence of stress. Varied HSP expressions seem to be very essential in the critical steps of embryonic and extra-embryonic structures formation and may correspond to cell movements, proliferation, morphogenesis and apoptosis, which occur during embryonic development. While our knowledge of detailed HSP expression patterns is in constant progress, their functions during embryonic development are not yet fully understood. In the paper, we review available data on HSP expression and discuss their role during vertebrate development.     

Soil application of Beauveria bassiana GHA against apple sawfly,Hoplocampa testudinea (Hymenoptera: Tenthredinidae): Field mortality and fungal persistence

Low impact alternatives to synthetic insecticides for the control of apple sawfly (Hoplocampa testudinea Klug) are scarce encumbering pest management in organic apple orchards. We investigated the soil persistence and field efficacy of the entomopathogenic fungus Beauveria bassiana (Balsamo) Vuillemin (BotaniGard) against apple sawfly under common organic orchard practices. We also assessed the efficacy of B. bassiana GHA and Metarhizium brunneum Petch (indigenous strain) against sawfly in the laboratory. Larvae treated with either fungus in the laboratory died faster than control larvae and displayed 49.4%–68.4% mycosis. In the field, B. bassiana density remained high in the week after application, during larval descent to the soil. Fungal density decreased to 25% at 49 d after application and to 0.4% after 55 weeks. Molecular markers revealed that the majority of fungal isolates recovered comprised the applied B. bassiana strain GHA. Larvae pupating in soil cages in the orchard for 49 d displayed 17% mycosis. The high efficacy under laboratory conditions was not seen in the field. B. bassiana application resulted in densities above the upper natural background level during the growing season, but reversion to background levels occurred within a year. It remains to be investigated whether this has a detrimental effect on nontarget organisms. Additional work is needed to bridge the knowledge gap between laboratory and field efficacy in orchards.