Size- and Ligand-Dependent Transport of Nanoparticles in Matricaria chamomilla as Demonstrated by Mass Spectroscopy and X-ray Fluorescence Imaging.

Matricaria chamomilla flowers were incubated with gold nanoparticles of different sizes ranging from 1.4 to 94 nm. After different incubation times of 6, 12, 24, and 48 h, the gold distribution in the flowers was destructively measured by inductively coupled plasma mass spectrometry (ICP-MS) and non-destructively measured by X-ray fluorescence imaging (XFI) with high lateral resolution. As a control, the biodistribution of iodine ions or iodine-containing organic molecules (iohexol) was determined, in order to demonstrate the feasibility of mapping the distribution of several elements in parallel. The results show a clear size-dependent transport of the nanoparticles. In addition, the surface chemistry also plays a decisive role in disposition. Only the 1.6 nm nanoparticles coated with acetylcysteine could be efficiently transported through the stem of the flowers into the petals. In this case, almost 80% of the nanoparticles which were found within each flower were located in the petals. The study also highlights the potential of XFI for in situ recording of in vivo analyte biodistribution.

Growth inhibition of an Araucaria angustifolia (Coniferopsida) fungal seed pathogen, Neofusicoccum parvum, by soil streptomycetes.

BACKGROUND: Araucariaceae are important forest trees of the southern hemisphere. Life expectancy of their seedlings can largely be reduced by fungal infections. In this study we have isolated and characterized such a fungus and investigated the potential of Streptomyces Actinobacteria from the respective rhizosphere to act as antagonists. RESULTS: The pathogenic fungus from Araucaria angustifolia seeds was identified by morphological markers (pore-associated Woronin-bodies) as belonging to the Pezizomycotina. Molecular data identified the fungus as Neofusicoccum parvum (Botryosphaeriaceae). Co-cultures on agar of this fungus with certain streptomycete isolates from the rhizosphere, and from the surface of Araucaria roots significantly reduced the growth of the fungus. HPLC analysis of the agar yielded streptomycete-specific exudate compounds which were partly identified. There were differences in compounds between single (bacteria, fungus) and dual cultures (bacteria + fungus). CONCLUSION: Streptomycetes from the rhizosphere of Araucariaceae produce exudates which can suppress the development of pathogenic fungi in their seeds.

Carbon allocation in ectomycorrhizal plants at limited optimal N supply: an attempt aat unraveling conflicting theories.

With regard to mycorrhiza, conflicting theories try to explain how the balance between fungal demand for carbohydrates and the plant's needs for nutrients varies, resulting in conflicting predictions. In order to evaluate current concepts, we investigated some metabolic parameters, which are indicative for plant carbon allocation in response to mycorrhization at limited and optimal N supply. Pinus pinaster seedlings were inoculated with living or dead (control) cultures of Pisolithus tinctorius, supplied with ammonium at 4 (limiting) or 7% d−1 (non-limiting) N relative addition rate (RARN), and followed development for 29 days. Mycorrhizal colonization of roots was quantified by the determination of ergosterol. A series of enzymes (sucrose and trehalose metabolism, anaplerosis) and metabolites (soluble carbohydrate, including trehalose; fructose 2,6 bisphosphate, free amino acids) relevant in the C/N exchange between symbionts, and in the carbon allocation and sink strength within the plant were assayed for 2-day-intervals for up to 14 days, and at 5-day-intervals for the rest of the experiment. The first 10 days reflected the establishment of mycorrhizal interaction, and the carbon allocation to the root was higher in M plants independent of N supply. Following this period, carbon allocation became N-related, higher at low, and lower at high N supply. The belowground C investment of M plants was dependent on N availability, but not on N gain. Finally, increased belowground C allocation was accompanied by a shift from plant to fungal metabolism.

Microgenomic analysis reveals cell type-specific gene expression patterns between ray and fusiform initials within the cambial meristem of Populus.

The vascular cambium is the meristem in trees that produce wood. This meristem consists of two types of neighbouring initials: fusiform cambial cells (FCCs), which give rise to the axial cell system (i.e. fibres and vessel elements), and ray cambial cells (RCCs), which give rise to rays. There is little molecular information on the mechanisms whereby the differing characteristics of these neighbouring cells are maintained. A microgenomic approach was adopted in which the transcriptomes of FCCs and RCCs dissected out from the cambial meristem of poplar (Populus trichocarpa x Populus deltoïdes var. Boelare) were analysed, and a transcriptional database for these two cell types established. Photosynthesis genes were overrepresented in RCCs, providing molecular support for the presence of photosynthetic systems in rays. Genes that putatively encode transporters (vesicle, lipid and metal ion transporters and aquaporins) in RCCs were also identified. In addition, many cell wall-related genes showed cell type-specific expression patterns. Notably, genes involved in pectin metabolism and xyloglucan metabolism were overrepresented in RCCs and FCCs, respectively. The results demonstrate the use of microgenomics to reveal differences in biological processes in neighbouring meristematic cells, and to identify key genes involved in these processes.

Expression of genes encoding chalcone synthase, flavanone 3-hydroxylase and dihydroflavonol 4-reductase correlates with flavanol accumulation during heartwood formation in Juglans nigra.

Heartwood formation is generally characterized by the accumulation of phenolic substances that increase the natural color and durability of wood. Although there is evidence that these substances are synthesized in aging sapwood cells, little is known about heartwood formation at the molecular level. We monitored seasonal changes in flavanol concentration across the stems of 23-year-old Juglans nigra L. trees by sampling growth rings extending from the differentiating xylem to the heartwood. We also analyzed expression of phenylpropanoid and flavonoid structural genes in these samples. In the sapwood-heartwood transition zone, flavanol accumulation was correlated with the transcription levels of the chalcone synthase (CHS) and flavanone 3-hydroxylase (F3H) genes. We also observed correlations between flavanol accumulation and the amount of dihydroflavonol 4-reductase (DFR) gene transcript in October, January and May. Although transcription of phenylalanine ammonia-lyase (PAL) and 4-coumarate:CoA ligase (4CL) genes did not correlate with flavanol accumulation, PAL genes were strongly expressed in the transition zone of samples collected in autumn, suggesting that their transcription in these tissues contributes to phenolic biosynthesis. Western immunoblotting showed that accumulation of CHS protein correlated with the amount of CHS gene transcript, whereas accumulation of PAL protein did not correlate with the the transcription levels PAL genes. Preliminary analyses revealed that PAL and CHS activities were higher in the transition zone than in the inner sapwood in autumn, winter, and spring. Thus, CHS activity could be regulated mainly at the transcriptional level, whereas post-translational modifications could modulate PAL activity. We conclude that flavanols are synthesized de novo in J. nigra sapwood cells that are undergoing transformation to heartwood.