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1.  An ellipsometric approach towards the description of inhomogeneous polymer-based Langmuir layers 
The applicability of nulling-based ellipsometric mapping as a complementary method next to Brewster angle microscopy (BAM) and imaging ellipsometry (IE) is presented for the characterization of ultrathin films at the air–water interface. First, the methodology is demonstrated for a vertically nonmoving Langmuir layer of star-shaped, 4-arm poly(ω-pentadecalactone) (PPDL-D4). Using nulling-based ellipsometric mapping, PPDL-D4-based inhomogeneously structured morphologies with a vertical dimension in the lower nm range could be mapped. In addition to the identification of these structures, the differentiation between a monolayer and bare water was possible. Second, the potential and limitations of this method were verified by applying it to more versatile Langmuir layers of telechelic poly[(rac-lactide)-co-glycolide]-diol (PLGA). All ellipsometric maps were converted into thickness maps by introduction of the refractive index that was derived from independent ellipsometric experiments, and the result was additionally evaluated in terms of the root mean square roughness, R q. Thereby, a three-dimensional view into the layers was enabled and morphological inhomogeneity could be quantified.
PMCID: PMC5082346  PMID: 27826490
ellipsometric mapping; Langmuir monolayer; polyester; root mean square roughness; spectroscopic ellipsometry
2.  2,4-D transport and herbicide resistance in weeds 
Journal of Experimental Botany  2016;67(11):3177-3179.
PMCID: PMC4892745  PMID: 27241489
ABCB transporters; auxin mimics; Brassicaceae; herbicide resistance; translocation; weeds.
3.  Towards a novel bioelectrocatalytic platform based on “wiring” of pyrroloquinoline quinone-dependent glucose dehydrogenase with an electrospun conductive polymeric fiber architecture 
Scientific Reports  2016;6:19858.
Electrospinning is known as a fabrication technique for electrode architectures that serve as immobilization matrices for biomolecules. The current work demonstrates a novel approach to construct a conductive polymeric platform, capable not only of immobilization, but also of electrical connection of the biomolecule with the electrode. It is produced upon electrospinning from mixtures of three different highly conductive sulfonated polyanilines and polyacrylonitrile on ITO electrodes. The resulting fiber mats are with a well-retained conductivity. After coupling the enzyme pyrroloquinoline quinone-dependent glucose dehydrogenase (PQQ-GDH) to polymeric structures and addition of the substrate glucose an efficient bioelectrocatalysis is demonstrated. Depending on the choice of the sulfonated polyanilline mediatorless bioelectrocatalysis starts at low potentials; no large overpotential is needed to drive the reaction. Thus, the electrospun conductive immobilization matrix acts here as a transducing element, representing a promising strategy to use 3D polymeric scaffolds as wiring agents for active enzymes. In addition, the mild and well reproducible fabrication process and the active role of the polymer film in withdrawing electrons from the reduced PQQ-GDH lead to a system with high stability. This could provide access to a larger group of enzymes for bioelectrochemical applications including biosensors and biofuel cells.
PMCID: PMC4731776  PMID: 26822141
4.  Soilless Plant Growth Media Influence the Efficacy of Phytohormones and Phytohormone Inhibitors 
PLoS ONE  2014;9(12):e107689.
Plant growth regulators, such as hormones and their respective biosynthesis inhibitors, are effective tools to elucidate the physiological function of phytohormones in plants. A problem of chemical treatments, however, is the potential for interaction of the active compound with the growth media substrate. We studied the interaction and efficacy of propiconazole, a potent and specific inhibitor of brassinosteroid biosynthesis, with common soilless greenhouse growth media for rice, sorghum, and maize. Many of the tested growth media interacted with propiconazole reducing its efficacy up to a hundred fold. To determine the molecular interaction of inhibitors with media substrates, Fourier Transform Infrared Spectroscopy and sorption isotherm analysis was applied. While mica clay substrates absorbed up to 1.3 mg of propiconazole per g substrate, calcined clays bound up to 12 mg of propiconazole per g substrate. The efficacy of the gibberellic acid biosynthesis inhibitor, uniconazole, and the most active brassinosteroid, brassinolide, was impacted similarly by the respective substrates. Conversely, gibberellic acid showed no distinct growth response in different media. Our results suggest that the reduction in efficacy of propiconazole, uniconazole, and brassinolide in bioassays when grown in calcined clay is caused by hydrophobic interactions between the plant growth regulators and the growth media. This was further confirmed by experiments using methanol-water solvent mixes with higher hydrophobicity values, which reduce the interaction of propiconazole and calcined clay.
PMCID: PMC4259294  PMID: 25485677
5.  Carboxylated or Aminated Polyaniline—Multiwalled Carbon Nanotubes Nanohybrids for Immobilization of Cellobiose Dehydrogenase on Gold Electrodes 
Biosensors  2014;4(4):370-386.
Polymer-multiwalled carbon nanotube (MWCNT) nanohybrids, which differ in surface charge have been synthesized to study the bioelectrocatalysis of adsorbed cellobiose dehydrogenase (CDH) from Phanerochaete sordida on gold electrodes. To obtain negatively charged nanohybrids, poly(3-amino-4-methoxybenzoic acid-co-aniline) (P(AMB-A)) was covalently linked to the surface of MWCNTs while modification with p-phenylenediamine (PDA) converted the COOH-groups to positively charged amino groups. Fourier transform infrared spectroscopy (FTIR) measurements verified the p-phenylenediamine (PDA) modification of the polymer-CNT nanohybrids. The positively charged nanohybrid MWCNT-P(AMB-A)-PDA promoted direct electron transfer (DET) of CDH to the electrode and bioelectrocatalysis of lactose was observed. Amperometric measurements gave an electrochemical response with KMapp = 8.89 mM and a current density of 410 nA/cm2 (15 mM lactose). The catalytic response was tested at pH 3.5 and 4.5. Interference by ascorbic acid was not observed. The study proves that DET between the MWCNT-P(AMB-A)-PDA nanohybrids and CDH is efficient and allows the sensorial detection of lactose.
PMCID: PMC4287708  PMID: 25587429
multiwalled carbon nanotubes; polyaniline; nanohybrids; cellobiose dehydrogenase
6.  Propiconazole Is a Specific and Accessible Brassinosteroid (BR) Biosynthesis Inhibitor for Arabidopsis and Maize 
PLoS ONE  2012;7(5):e36625.
Brassinosteroids (BRs) are steroidal hormones that play pivotal roles during plant development. In addition to the characterization of BR deficient mutants, specific BR biosynthesis inhibitors played an essential role in the elucidation of BR function in plants. However, high costs and limited availability of common BR biosynthetic inhibitors constrain their key advantage as a species-independent tool to investigate BR function. We studied propiconazole (Pcz) as an alternative to the BR inhibitor brassinazole (Brz). Arabidopsis seedlings treated with Pcz phenocopied BR biosynthetic mutants. The steady state mRNA levels of BR, but not gibberellic acid (GA), regulated genes increased proportional to the concentrations of Pcz. Moreover, root inhibition and Pcz-induced expression of BR biosynthetic genes were rescued by 24epi-brassinolide, but not by GA3 co-applications. Maize seedlings treated with Pcz showed impaired mesocotyl, coleoptile, and true leaf elongation. Interestingly, the genetic background strongly impacted the tissue specific sensitivity towards Pcz. Based on these findings we conclude that Pcz is a potent and specific inhibitor of BR biosynthesis and an alternative to Brz. The reduced cost and increased availability of Pcz, compared to Brz, opens new possibilities to study BR function in larger crop species.
PMCID: PMC3348881  PMID: 22590578
7.  The compact Selaginella genome identifies changes in gene content associated with the evolution of vascular plants 
Banks, Jo Ann | Nishiyama, Tomoaki | Hasebe, Mitsuyasu | Bowman, John L. | Gribskov, Michael | dePamphilis, Claude | Albert, Victor A. | Aono, Naoki | Aoyama, Tsuyoshi | Ambrose, Barbara A. | Ashton, Neil W. | Axtell, Michael J. | Barker, Elizabeth | Barker, Michael S. | Bennetzen, Jeffrey L. | Bonawitz, Nicholas D. | Chapple, Clint | Cheng, Chaoyang | Correa, Luiz Gustavo Guedes | Dacre, Michael | DeBarry, Jeremy | Dreyer, Ingo | Elias, Marek | Engstrom, Eric M. | Estelle, Mark | Feng, Liang | Finet, Cédric | Floyd, Sandra K. | Frommer, Wolf B. | Fujita, Tomomichi | Gramzow, Lydia | Gutensohn, Michael | Harholt, Jesper | Hattori, Mitsuru | Heyl, Alexander | Hirai, Tadayoshi | Hiwatashi, Yuji | Ishikawa, Masaki | Iwata, Mineko | Karol, Kenneth G. | Koehler, Barbara | Kolukisaoglu, Uener | Kubo, Minoru | Kurata, Tetsuya | Lalonde, Sylvie | Li, Kejie | Li, Ying | Litt, Amy | Lyons, Eric | Manning, Gerard | Maruyama, Takeshi | Michael, Todd P. | Mikami, Koji | Miyazaki, Saori | Morinaga, Shin-ichi | Murata, Takashi | Mueller-Roeber, Bernd | Nelson, David R. | Obara, Mari | Oguri, Yasuko | Olmstead, Richard G. | Onodera, Naoko | Petersen, Bent Larsen | Pils, Birgit | Prigge, Michael | Rensing, Stefan A. | Riaño-Pachón, Diego Mauricio | Roberts, Alison W. | Sato, Yoshikatsu | Scheller, Henrik Vibe | Schulz, Burkhard | Schulz, Christian | Shakirov, Eugene V. | Shibagaki, Nakako | Shinohara, Naoki | Shippen, Dorothy E. | Sørensen, Iben | Sotooka, Ryo | Sugimoto, Nagisa | Sugita, Mamoru | Sumikawa, Naomi | Tanurdzic, Milos | Theißen, Günter | Ulvskov, Peter | Wakazuki, Sachiko | Weng, Jing-Ke | Willats, William W.G.T. | Wipf, Daniel | Wolf, Paul G. | Yang, Lixing | Zimmer, Andreas D. | Zhu, Qihui | Mitros, Therese | Hellsten, Uffe | Loqué, Dominique | Otillar, Robert | Salamov, Asaf | Schmutz, Jeremy | Shapiro, Harris | Lindquist, Erika | Lucas, Susan | Rokhsar, Daniel | Grigoriev, Igor V.
Science (New York, N.Y.)  2011;332(6032):960-963.
Vascular plants appeared ~410 million years ago then diverged into several lineages of which only two survive: the euphyllophytes (ferns and seed plants) and the lycophytes (1). We report here the genome sequence of the lycophyte Selaginella moellendorffii (Selaginella), the first non-seed vascular plant genome reported. By comparing gene content in evolutionary diverse taxa, we found that the transition from a gametophyte- to sporophyte-dominated life cycle required far fewer new genes than the transition from a non-seed vascular to a flowering plant, while secondary metabolic genes expanded extensively and in parallel in the lycophyte and angiosperm lineages. Selaginella differs in post-transcriptional gene regulation, including small RNA regulation of repetitive elements, an absence of the tasiRNA pathway and extensive RNA editing of organellar genes.
PMCID: PMC3166216  PMID: 21551031
8.  Geometric Constraints and the Anatomical Interpretation of Twisted Plant Organ Phenotypes 
The study of plant mutants with twisting growth in axial organs, which normally grow straight in the wild-type, is expected to improve our understanding of the interplay among microtubules, cellulose biosynthesis, cell wall structure, and organ biomechanics that control organ growth and morphogenesis. However, geometric constraints based on symplastic growth and the consequences of these geometric constraints concerning interpretations of twisted-organ phenotypes are currently underestimated. Symplastic growth, a fundamental concept in plant developmental biology, is characterized by coordinated growth of adjacent cells based on their connectivity through cell walls. This growth behavior implies that in twisting axial organs, all cell files rotate in phase around the organ axis, as has been illustrated for the Arabidopsis spr1 and twd1 mutants in this work. Evaluating the geometry of such organs, we demonstrate that a radial gradient in cell elongation and changes in cellular growth anisotropy must occur in twisting organs out of geometric necessity alone. In-phase rotation of the different cell layers results in a decrease of length and angle toward organ axis from the outer cell layers inward. Additionally, the circumference of each cell layer increases in twisting organs, which requires compensation through radial expansion or an adjustment of cell number. Therefore, differential cell elongation and growth anisotropy cannot serve as arguments for or against specific hypotheses regarding the molecular cause of twisting growth. We suggest instead, that based on mathematical modeling, geometric constraints in twisting organs are indispensable for the explanation of the causal connection of molecular and biomechanical processes in twisting as well as normal organs.
PMCID: PMC3355744  PMID: 22645544
Arabidopsis thaliana, developmental biomechanics; spiral1 (spr1) mutant; symplastic growth; tissue geometry; tissue tension; twisted dwarf1 (twd1) mutant; twisting growth
9.  Arabidopsis brassinosteroid biosynthetic mutant dwarf7-1 exhibits slower rates of cell division and shoot induction 
BMC Plant Biology  2010;10:270.
Plant growth depends on both cell division and cell expansion. Plant hormones, including brassinosteroids (BRs), are central to the control of these two cellular processes. Despite clear evidence that BRs regulate cell elongation, their roles in cell division have remained elusive.
Here, we report results emphasizing the importance of BRs in cell division. An Arabidopsis BR biosynthetic mutant, dwarf7-1, displayed various characteristics attributable to slower cell division rates. We found that the DWARF4 gene which encodes for an enzyme catalyzing a rate-determining step in the BR biosynthetic pathways, is highly expressed in the actively dividing callus, suggesting that BR biosynthesis is necessary for dividing cells. Furthermore, dwf7-1 showed noticeably slower rates of callus growth and shoot induction relative to wild-type control. Flow cytometric analyses of the nuclei derived from either calli or intact roots revealed that the cell division index, which was represented as the ratio of cells at the G2/M vs. G1 phases, was smaller in dwf7-1 plants. Finally, we found that the expression levels of the genes involved in cell division and shoot induction, such as PROLIFERATING CELL NUCLEAR ANTIGEN2 (PCNA2) and ENHANCER OF SHOOT REGENERATION2 (ESR2), were also lower in dwf7-1 as compared with wild type.
Taken together, results of callus induction, shoot regeneration, flow cytometry, and semi-quantitative RT-PCR analysis suggest that BRs play important roles in both cell division and cell differentiation in Arabidopsis.
PMCID: PMC3017067  PMID: 21143877
10.  Evaluating the function of putative hormone transporters 
Plant Signaling & Behavior  2009;4(2):147-148.
Hormones typically serve as long distance signaling molecules. To reach their site of action, hormones need to be transported from the sites of synthesis. Many plant hormones are mobile, thus requiring specific transport systems for the export from their source cells as well as subsequent import into target cells. Hormone transport in general is still poorly understood. Auxin is probably the most intensively studied plant hormone concerning transport in the moment. To advance our understanding of hormone transport we need two principal data sets: information on the properties of the transport systems including substrate specificity and kinetics, and we need to identify candidate genes for the respective transporters. Physiological transport data can provide an important basis for identifying and characterizing candidate transporters and to define their in vivo role. A recent publication in Plant Physiology highlights how kinetic and specificity studies may help to identify cytokinin transporters.1
PMCID: PMC2637505  PMID: 19649195
kinetin; zeatin; adenine; phytohormone; transport
11.  Crystallization and preliminary X-ray analysis of immunophilin-like FKBP42 from Arabidopsis thaliana  
The crystallization of FKBP42, a multi-domain member of the FK506-binding protein family, from the plant A. thaliana is reported.
Two fragments of FKBP42 from Arabidopsis thaliana covering differing lengths of the molecule have been expressed, purified and crystallized. For each construct, crystals belonging to two different space groups were obtained and subjected to preliminary X-ray analysis.
PMCID: PMC1952426  PMID: 16511041
FKBP42; FK506-binding proteins
12.  Arabidopsis Immunophilin-like TWD1 Functionally Interacts with Vacuolar ABC Transporters 
Molecular Biology of the Cell  2004;15(7):3393-3405.
Previously, the immunophilin-like protein TWD1 from Arabidopsis has been demonstrated to interact with the ABC transporters AtPGP1 and its closest homologue, AtPGP19. Physiological and biochemical investigation of pgp1/pgp19 and of twd1 plants suggested a regulatory role of TWD1 on AtPGP1/AtPGP19 transport activities. To further understand the dramatic pleiotropic phenotype that is caused by loss-of-function mutation of the TWD1 gene, we were interested in other TWD1 interacting proteins. AtMRP1, a multidrug resistance-associated (MRP/ABCC)-like ABC transporter, has been isolated in a yeast two-hybrid screen. We demonstrate molecular interaction between TWD1 and ABC transporters AtMRP1 and its closest homologue, AtMRP2. Unlike AtPGP1, AtMRP1 binds to the C-terminal tetratricopeptide repeat domain of TWD1, which is well known to mediate protein-protein interactions. Domain mapping proved that TWD1 binds to a motif of AtMRP1 that resembles calmodulin-binding motifs; and calmodulin binding to the C-terminus of MRP1 was verified. By membrane fractionation and GFP-tagging, we localized AtMRP1 to the central vacuolar membrane and the TWD1-AtMRP1 complex was verified in vivo by coimmunoprecipitation. We were able to demonstrate that TWD1 binds to isolated vacuoles and has a significant impact on the uptake of metolachlor-GS and estradiol-β-glucuronide, well-known substrates of vacuolar transporters AtMRP1 and AtMRP2.
PMCID: PMC452592  PMID: 15133126
13.  TWISTED DWARF1, a Unique Plasma Membrane-anchored Immunophilin-like Protein, Interacts with Arabidopsis Multidrug Resistance-like Transporters AtPGP1 and AtPGP19 
Molecular Biology of the Cell  2003;14(10):4238-4249.
Null-mutations of the Arabidopsis FKBP-like immunophilin TWISTED DWARF1 (TWD1) gene cause a pleiotropic phenotype characterized by reduction of cell elongation and disorientated growth of all plant organs. Heterologously expressed TWD1 does not exhibit cis-trans-peptidylprolyl isomerase (PPIase) activity and does not complement yeast FKBP12 mutants, suggesting that TWD1 acts indirectly via protein-protein interaction. Yeast two-hybrid protein interaction screens with TWD1 identified cDNA sequences that encode the C-terminal domain of Arabidopsis multidrugresistance-like ABC transporter AtPGP1. This interaction was verified in vitro. Mapping of protein interaction domains shows that AtPGP1 surprisingly binds to the N-terminus of TWD1 harboring the cis-trans peptidyl-prolyl isomerase-like domain and not to the tetratrico-peptide repeat domain, which has been shown to mediate protein-protein interaction. Unlike all other FKBPs, TWD1 is shown to be an integral membrane protein that colocalizes with its interacting partner AtPGP1 on the plasma membrane. TWD1 also interacts with AtPGP19 (AtMDR1), the closest homologue of AtPGP1. The single gene mutation twd1-1 and double atpgp1-1/atpgp19-1 (atmdr1-1) mutants exhibit similar phenotypes including epinastic growth, reduced inflorescence size, and reduced polar auxin transport, suggesting that a functional TWD1-AtPGP1/AtPGP19 complex is required for proper plant development.
PMCID: PMC207015  PMID: 14517332

Results 1-13 (13)