Ivan Paponov

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(+47) 404 80 316
ivan.paponov@nibio.no

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Postvegen 213, NO-4353 Klepp stasjon

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Sammendrag

Auxin is a molecule, which controls many aspects of plant development through both transcriptional and non-transcriptional signaling responses. AUXIN BINDING PROTEIN1 (ABP1) is a putative receptor for rapid non-transcriptional auxin-induced changes in plasma membrane depolarization and endocytosis rates. However, the mechanism of ABP1-mediated signaling is poorly understood. Here we show that membrane depolarization and endocytosis inhibition are ABP1-independent responses and that auxin-induced plasma membrane depolarization is instead dependent on the auxin influx carrier AUX1. AUX1 was itself not involved in the regulation of endocytosis. Auxin-dependent depolarization of the plasma membrane was also modulated by the auxin efflux carrier PIN2. These data establish a new connection between auxin transport and non-transcriptional auxin signaling.

Sammendrag

Rhodiola rosea is a perennial flowering plant with a long history as a medicine plant. The plant contain a range of bioactive compounds including salidroside, rosavin, rosarian and rosin. Some of the compounds are characterized as adaptogens, meaning they can increase the body’s resistance to various stressors. An increased demand for better pharmaceuticals has stimulated the development of new methods for agricultural as well as in vitro cultivation of medicinal plants. A new technology, called rhizosecretion of biologically active chemicals, can provide a continuous supply of biologically active compounds over the lifetime of plants. The plants will then be grown under controlled conditions. In order to increase the production of bioactive compounds in Rhodiola rosea under these conditions it is therefore hypothesized that the biosynthesis can be upregulated by growing it under specific temperature and light quality treatments. An experiment with different light and temperature regimes was established for optimal accumulation of biologically active compounds. Four different clones of Rhodiola rosea were grown under three different light conditions (red, blue and white) combined with two different temperatures (9 and 18 °C) for three weeks. The gene expression of Tyrosine decarboxylase (TyrDC), found to have a key role in the biosynthesis of salidroside, were investigated. In addition, the content of various bioactive compounds were quantified before and after treatment. The results indicate that use if high producing clones is most important for high production and that there is a short-term upregulation during blue light treatment. During the three-week treatment, there was no significant effect of the temperature treatments.

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The Earth magnetic field (or geomagnetic field, GMF) is a natural component of our planet and variations of the GMF are perceived by plants with a still uncharacterized magnetoreceptor. The purpose of this work was to assess the effect of near null magnetic field (NNMF, ∼40 nT) on Arabidopsis thaliana Col0 root ion modulation. A time-course (from 10 min to 96 h) exposure of Arabidopsis to NNMF was compared to GMF and the content of some cations (NH4 +, K+, Ca2+ and Mg2+) and anions (Cl−, SO4 =, NO3 − and PO4 =) was evaluated by capillary electrophoresis. The expression of several cation and anion channel- and transporter-related genes was assessed by gene microarray. A few minutes after exposure to NNMF, Arabidopsis roots responded with a significant change in the content and gene expression of all nutrient ions under study, indicating the presence of a plant magnetoreceptor that responds immediately to MF variations by modulating channels, transporters and genes involved in mineral nutrition. The response of Arabidopsis to reduced MF was a general reduction of plant ion uptake and transport. Our data suggest the importance to understand the nature and function of the plant magnetoreceptor for future space programs involving plant growth in environments with a reduced MF.

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 Auxin gradients are sustained by series of influx and efflux carriers whose subcellular local- ization is sensitive to both exogenous and endogenous factors. Recently the localization of the Arabidopsis thaliana auxin efflux carrier PIN-FORMED (PIN) 6 was reported to be tissue- specific and regulated through unknown mechanisms.  Here, we used genetic, molecular and pharmacological approaches to characterize the molecular mechanism(s) controlling the subcellular localization of PIN6.  PIN6 localizes to endomembrane domains in tissues with low PIN6 expression levels such as roots, but localizes at the plasma membrane (PM) in tissues with increased PIN6 expression such as the inflorescence stem and nectary glands. We provide evidence that this dual local- ization is controlled by PIN6 phosphorylation and demonstrate that PIN6 is phosphorylated by mitogen-activated protein kinases (MAPKs) MPK4 and MPK6. The analysis of transgenic plants expressing PIN6 at PM or in endomembrane domains reveals that PIN6 subcellular localization is critical for Arabidopsis inflorescence stem elongation post-flowering (bolting). In line with a role for PIN6 in plant bolting, inflorescence stems elongate faster in pin6 mutant plants than in wild-type plants.  We propose that PIN6 subcellular localization is under the control of developmental signals acting on tissue-specific determinants controlling PIN6-expression levels and PIN6 phosphorylation.