| 1. |
- Bhalerao, Rishikesh P., et al.
(författare)
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Auxin gradients across wood – instructive or incidental?
- 2014
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Ingår i: Physiologia Plantarum. - : Wiley. - 0031-9317 .- 1399-3054. ; 151, s. 43-51
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Forskningsöversikt (refereegranskat)abstract
- Various aspects of wood formation have been linked to the action of auxin, e.g. cambial activity, dormancy, secondary cell wall deposition and tension wood formation. The presence of a radial auxin concentration gradient across wood-forming tissue has been suggested to regulate cambial activity and differentiation of cambial derivatives by providing positional information to cells within the tissue. Similar patterning mechanisms that depend on the interpretation of auxin thresholds have subsequently been proposed for shoot and root apical meristems. However, direct evidence for the existence of auxin gradients has only been obtained for the cambium of various tree species. While the auxin gradient theory is based on a plethora of descriptive and pharmacological experiments, in recent years, auxin function on wood formation has been underpinned by molecular and functional data. Here, we review the latest progress in understanding the role of auxin in wood formation and discuss how auxin concentration gradients could be established and interpreted in wood-forming tissues.
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| 2. |
- Fischer, Urs
(författare)
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The heterozygous abp1/ABP1 insertional mutant has defects in functions requiring polar auxin transport and in regulation of early auxin-regulated genes
- 2011
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Ingår i: Plant Journal. - 0960-7412 .- 1365-313X. ; 65, s. 282-294
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Tidskriftsartikel (refereegranskat)abstract
- P>AUXIN-BINDING PROTEIN 1 (ABP1) is not easily accessible for molecular studies because the homozygous T-DNA insertion mutant is embryo-lethal. We found that the heterozygous abp1/ABP1 insertion mutant has defects in auxin physiology-related responses: higher root slanting angles, longer hypocotyls, agravitropic roots and hypocotyls, aphototropic hypocotyls, and decreased apical dominance. Heterozygous plants flowered earlier than wild-type plants under short-day conditions. The length of the main root, the lateral root density and the hypocotyl length were little altered in the mutant in response to auxin. Compared to wild-type plants, transcription of early auxin-regulated genes (IAA2, IAA11, IAA13, IAA14, IAA19, IAA20, SAUR9, SAUR15, SAUR23, GH3.5 and ABP1) was less strongly up-regulated in the mutant by 0.1, 1 and 10 mu m IAA. Surprisingly, ABP1 was itself an early auxin-up-regulated gene. IAA uptake into the mutant seedlings during auxin treatments was indistinguishable from wild-type. Basipetal auxin transport in young roots was slower in the mutant, indicating a PIN2/EIR1 defect, while acropetal transport was indistinguishable from wild-type. In the eir1 background, three of the early auxin-regulated genes tested (IAA2, IAA13 and ABP1) were more strongly induced by 1 mu m IAA in comparison to wild-type, but eight of them were less up-regulated in comparison to wild-type. Similar but not identical disturbances in regulation of early auxin-regulated genes indicate tight functional linkage of ABP1 and auxin transport regulation. We hypothesize that ABP1 is involved in the regulation of polar auxin transport, and thus affects local auxin concentration and early auxin gene regulation. In turn, ABP1 itself is under the transcriptional control of auxin.
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| 3. |
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| 4. |
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| 5. |
- Kaufmann, Patrik, et al.
(författare)
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Ammonium and non-sea salt sulfate in the EPICA ice cores as indicator of biological activity in the Southern Ocean
- 2010
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Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 29:02-jan, s. 313-323
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Tidskriftsartikel (refereegranskat)abstract
- Sulfate (SO42-) and ammonium (NH4+) flux records over the last 150,000 years from both Antarctic EPICA ice cores (European Project for Ice Coring in Antarctica) are presented. The ice core record from Dome C is influenced by the Indian sector of the Southern Ocean (SO), whereas Dronning Maud Land is facing the Atlantic sector. Generally, they reflect the past atmospheric aerosol load and, thus, potentially reveal the fingerprint of marine biogenic sources from the SO. The most important feature of both, the nssSO(4)(2-) as well as NH4+ flux records, is the absence of any significant glacial cycles, in contrary to the distinct transitions for mineral dust and sea salt aerosol over the last 150,000 years. This finding challenges the iron fertilization hypothesis on long time scales, as the significant changes in dust, e.g. from the last glacial maximum toward the Holocene have neither an impact on nssSO(4)(2-) nor on NH4+ fluxes found in interior Antarctica. The inter-site correlation of both species is weak, r(2) = 0.42 for the nssSO(4)(2-) flux and r(2) = 0.12 for the NH4+ flux respectively, emphasizing the local Source characteristics of biogenic aerosol from the SO. Millennial variability in NH4+ and nssSO(4)(2-) is within the uncertainty of our flux estimates. Correlation with mineral dust and sea ice derived sodium shows only a very weak influence of dust deposition on those insignificant changes in nssSO(4)(2-) flux for the Atlantic sector of the Southern Ocean, but also small transport changes or terrigeneous sulfate contributions may contribute to those variations at EDML.
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| 6. |
- Liebsch, Daniela, et al.
(författare)
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Class I KNOX transcription factors promote differentiation of cambial derivatives into xylem fibers in the Arabidopsis hypocotyl
- 2014
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Ingår i: Development. - : The Company of Biologists. - 0950-1991 .- 1477-9129. ; 141, s. 4311-4319
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Tidskriftsartikel (refereegranskat)abstract
- The class I KNOX transcription factors SHOOT MERISTEMLESS (STM) and KNAT1 are important regulators of meristem maintenance in shoot apices, with a dual role of promoting cell proliferation and inhibiting differentiation. We examined whether they control stem cell maintenance in the cambium of Arabidopsis hypocotyls, a wood-forming lateral meristem, in a similar fashion as in the shoot apical meristem. Weak loss-of-function alleles of KNAT1 and STM led to reduced formation of xylem fibers - highly differentiated cambial derivatives - whereas cell proliferation in the cambium was only mildly affected. In a knat1;stm double mutant, xylem fiber differentiation was completely abolished, but residual cambial activity was maintained. Expression of early and late markers of xylary cell differentiation was globally reduced in the knat1; stm double mutant. KNAT1 and STM were found to act through transcriptional repression of the meristem boundary genes BLADE-ON-PETIOLE 1 (BOP1) and BOP2 on xylem fiber differentiation. Together, these data indicate that, in the cambium, KNAT1 and STM, contrary to their function in the shoot apical meristem, promote cell differentiation through repression of BOP genes.
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| 7. |
- Lundberg-Felten, Judith, et al.
(författare)
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Arabidopsis WAT1 is a vacuolar auxin transport facilitator required for auxin homoeostasis
- 2013
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Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 4
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Tidskriftsartikel (refereegranskat)abstract
- The plant hormone auxin (indole-3-acetic acid, IAA) has a crucial role in plant development. Its spatiotemporal distribution is controlled by a combination of biosynthetic, metabolic and transport mechanisms. Four families of auxin transporters have been identified that mediate transport across the plasma or endoplasmic reticulum membrane. Here we report the discovery and the functional characterization of the first vacuolar auxin transporter. We demonstrate that WALLS ARE THIN1 (WAT1), a plant-specific protein that dictates secondary cell wall thickness of wood fibres, facilitates auxin export from isolated Arabidopsis vacuoles in yeast and in Xenopus oocytes. We unambiguously identify IAA and related metabolites in isolated Arabidopsis vacuoles, suggesting a key role for the vacuole in intracellular auxin homoeostasis. Moreover, local auxin application onto wat1 mutant stems restores fibre cell wall thickness. Our study provides new insight into the complexity of auxin transport in plants and a means to dissect auxin function during fibre differentiation.
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