Mon. 12 Oct, 2015 - Sun. 18 Oct, 2015
Thu. 15 Oct, 2015
Seminar - Stefano Manzoni
Thu. 15 Oct, 2015 14:00 - 16:00
Speaker: Stefano Manzoni – Department of Physical Geography, Stockholm University
Title: Eco-hydrological optimality explains global patterns in plant hydraulic traits
Time & Place: Thursday 15th October 2015 14:00-15:00 Room KB3B3
Abstract: Plant hydraulic traits exhibit both trade-offs (e.g., xylem safety vs. efficiency) and coordination (e.g., correlation of liquid- and gas-phase conductances). While some of these patterns can be explained by physiological features at the conduit scale, here we present the hypothesis that trait coordination and trade-offs can emerge from eco-hydrological optimality criteria. In the short-term and in moist conditions, plants need to transport water fast to match the atmospheric evaporative demand, which causes a steep water potential gradient between leaves and soil. The larger this gradient, the higher the transpiration rate, until cavitation ensues and xylem hydraulic conductivity is decreased. Hence, there is a tradeoff between hydraulic efficiency and driving force, resulting in maximum transpiration rates at intermediate values of leaf water potential. Using a minimalist model of plant hydraulics, we show that maximum transpiration can be attained when saturated hydraulic conductivity and resistance to cavitation are inversely proportional (i.e., there is a xylem safety vs. efficiency trade-off), and that indeed maximum rates are reached across biomes. Plants also need to use soil water effectively when it becomes limiting. To do so, two strategies might be selected for: avoidance of hydraulic failure in dry periods and long-term maximization of transpiration rate (assumed as a proxy for plant fitness). Results show that both strategies require that stomatal closure is coordinated with loss of conductivity due to cavitation. Moreover, the optimal combinations of xylem and stomatal traits depend on both total rainfall and its distribution during the growing season. Drier conditions or intense rainfall events interspaced by prolonged dry spells favor plants with high resistance to cavitation and delayed stomatal closure as soils dry. In contrast, plants in mesic conditions benefit from cavitation prevention through earlier stomatal closure. The proposed eco-hydrological optimality criteria can be used as analytical tools to interpret variability in plant water use and predict trends in plant productivity and species composition under future climates.
Title: Eco-hydrological optimality explains global patterns in plant hydraulic traits
Time & Place: Thursday 15th October 2015 14:00-15:00 Room KB3B3
Abstract: Plant hydraulic traits exhibit both trade-offs (e.g., xylem safety vs. efficiency) and coordination (e.g., correlation of liquid- and gas-phase conductances). While some of these patterns can be explained by physiological features at the conduit scale, here we present the hypothesis that trait coordination and trade-offs can emerge from eco-hydrological optimality criteria. In the short-term and in moist conditions, plants need to transport water fast to match the atmospheric evaporative demand, which causes a steep water potential gradient between leaves and soil. The larger this gradient, the higher the transpiration rate, until cavitation ensues and xylem hydraulic conductivity is decreased. Hence, there is a tradeoff between hydraulic efficiency and driving force, resulting in maximum transpiration rates at intermediate values of leaf water potential. Using a minimalist model of plant hydraulics, we show that maximum transpiration can be attained when saturated hydraulic conductivity and resistance to cavitation are inversely proportional (i.e., there is a xylem safety vs. efficiency trade-off), and that indeed maximum rates are reached across biomes. Plants also need to use soil water effectively when it becomes limiting. To do so, two strategies might be selected for: avoidance of hydraulic failure in dry periods and long-term maximization of transpiration rate (assumed as a proxy for plant fitness). Results show that both strategies require that stomatal closure is coordinated with loss of conductivity due to cavitation. Moreover, the optimal combinations of xylem and stomatal traits depend on both total rainfall and its distribution during the growing season. Drier conditions or intense rainfall events interspaced by prolonged dry spells favor plants with high resistance to cavitation and delayed stomatal closure as soils dry. In contrast, plants in mesic conditions benefit from cavitation prevention through earlier stomatal closure. The proposed eco-hydrological optimality criteria can be used as analytical tools to interpret variability in plant water use and predict trends in plant productivity and species composition under future climates.
Fri. 16 Oct, 2015
Seminar - Simon Hawkins
Fri. 16 Oct, 2015 10:00 - 11:00
Speaker: Simon Hawkins – Plant Fiber Team, UGSF, UMR CNRS 8576. University of Lille 1, France
Title: Organ-specific proteomics and targeted cell wall analyses in flax
Time & Place: Friday 16th October 2015 10:00-11:00 Room KB3B3
Abstract: Flax (Linum usitatissimum L.) is a fiber plant species that has been used since antiquity for the fabrication of textiles (linen), as well as for the production of oil (linseed). Flax is also an excellent model to study cell wall biology as the inner- and outer-stem tissues of this plant contain cells with highly contrasted wall compositions. Cells from the inner xylem core have heavily lignified secondary cell walls containing up to 31 % lignin whereas the thick secondary cell walls of the long bast fibers present in outer stem tissues are richer in cellulose and contain only 4 % lignin. The use of an organ-specific proteomics approach allowed us to identify 1,242 non-redundant proteins present in 3 different fractions (soluble, membrane and cell wall) from 4 different flax organs (inner-/outer-stems, leaves and roots). Subsequent analyses of these proteins, as well as of other published flax proteomics data, enabled us to identify 405 proteins potentially involved in cell wall metabolism in this species. A study of potential protein networks using STRING (http://string-db.org) underlined organ-/tissue-specific differences in protein networks potentially related to contrasted cell wall structure/metabolisms. Phylogenetic analyses of the flax cell wall proteins also allowed us to identify a marked paralogy in the XTH (Xyloglucan endotransglucosylase/hydrolase) IIIA family involved in cell wall remodeling events and potentially associated with the differentiation of flax bast fibers.
Title: Organ-specific proteomics and targeted cell wall analyses in flax
Time & Place: Friday 16th October 2015 10:00-11:00 Room KB3B3
Abstract: Flax (Linum usitatissimum L.) is a fiber plant species that has been used since antiquity for the fabrication of textiles (linen), as well as for the production of oil (linseed). Flax is also an excellent model to study cell wall biology as the inner- and outer-stem tissues of this plant contain cells with highly contrasted wall compositions. Cells from the inner xylem core have heavily lignified secondary cell walls containing up to 31 % lignin whereas the thick secondary cell walls of the long bast fibers present in outer stem tissues are richer in cellulose and contain only 4 % lignin. The use of an organ-specific proteomics approach allowed us to identify 1,242 non-redundant proteins present in 3 different fractions (soluble, membrane and cell wall) from 4 different flax organs (inner-/outer-stems, leaves and roots). Subsequent analyses of these proteins, as well as of other published flax proteomics data, enabled us to identify 405 proteins potentially involved in cell wall metabolism in this species. A study of potential protein networks using STRING (http://string-db.org) underlined organ-/tissue-specific differences in protein networks potentially related to contrasted cell wall structure/metabolisms. Phylogenetic analyses of the flax cell wall proteins also allowed us to identify a marked paralogy in the XTH (Xyloglucan endotransglucosylase/hydrolase) IIIA family involved in cell wall remodeling events and potentially associated with the differentiation of flax bast fibers.
PhD Thesis defence - Henrik Serk
Fri. 16 Oct, 2015 13:30 - 14:30
Title: Cellular Aspects of Lignin Biosynthesis in Xylem Vessels of Zinnia and Arabidopsis
Defendant: Henrik Srk
Opponent: Prof. Simon Hawkins, Department of Functional and Structural Glycobiology, University of Lille, France.
Time & Place: 16:th of October 2016, 13.30
Abstract:
Lignin is the second most abundant biopolymer on earth and is found in the xylem (wood) of vascular land plants. To transport the hydro-mineral sap, xylem forms specialized cells, called tracheary elements (TEs), which are hollow dead cylinders reinforced with lateral secondary cell walls (SCW). These SCWs incorporate lignin to gain mechanical strength, water impermeability and resistance against pathogens. The aim of this thesis is to understand the spatio-temporal deposition of lignin during TE differentiation and the relationship with its neighbouring cells. In vitro TE differentiating cell cultures of Zinnia elegans and Arabidopsis thaliana are ideal tools to study this process: cells differentiate simultaneously into 30-50% TEs while the rest remain parenchymatic (non-TEs). Live-cell imaging of such TEs indicated that lignification occurs after programmed cell death (PCD), in a non-cell autonomous manner, in which the non-TEs provide the lignin monomers.
This thesis confirms that lignification occurs and continues long after TE PCD in both in vitro TE cultures and whole plants. The cooperative supply of lignin monomers by the non-TEs was first demonstrated by using in vitro TE cultures and confirmed in whole plants by using lignin monomer synthesis gene mutants that exhibit a reduction in TE lignification. The XP specific complementation of these mutants led to nearly completely rescuing the TE lignin reduction of the mutants. Experiments with in vitro TE cultures further revealed that non-TEs supply reactive oxygen species (ROS) to TEs and that ROS are required for TE post-mortem lignification. Non-TEs exhibit further an enlarged nucleus with increased DNA content, thus indicating that non-TEs are in fact endoreplicated xylem parenchyma (XP) cells. Microscopic analysis of the spatial distribution of lignin in in vitro TE cultures and whole plants revealed that lignification is restricted to TE SCWs in both protoxylem and metaxylem. These specific lignin deposition domains were found to be established by phenoloxidases, i.e. laccases and peroxidases. Laccases were cell-autonomously produced by developing TEs, indicating that the deposition domains are defined before PCD.
Altogether, these results highlight that the hydro-mineral sap conduction through TEs is enabled by the spatially and temporally controlled lignification of the SCW. Lignification occurs post-mortem by the supply of monomers and ROS from neighboring XP cells and is restricted to specific deposition domains, defined by the pre-mortem production of phenoloxidases.
Defendant: Henrik Srk
Opponent: Prof. Simon Hawkins, Department of Functional and Structural Glycobiology, University of Lille, France.
Time & Place: 16:th of October 2016, 13.30
Abstract:
Lignin is the second most abundant biopolymer on earth and is found in the xylem (wood) of vascular land plants. To transport the hydro-mineral sap, xylem forms specialized cells, called tracheary elements (TEs), which are hollow dead cylinders reinforced with lateral secondary cell walls (SCW). These SCWs incorporate lignin to gain mechanical strength, water impermeability and resistance against pathogens. The aim of this thesis is to understand the spatio-temporal deposition of lignin during TE differentiation and the relationship with its neighbouring cells. In vitro TE differentiating cell cultures of Zinnia elegans and Arabidopsis thaliana are ideal tools to study this process: cells differentiate simultaneously into 30-50% TEs while the rest remain parenchymatic (non-TEs). Live-cell imaging of such TEs indicated that lignification occurs after programmed cell death (PCD), in a non-cell autonomous manner, in which the non-TEs provide the lignin monomers.
This thesis confirms that lignification occurs and continues long after TE PCD in both in vitro TE cultures and whole plants. The cooperative supply of lignin monomers by the non-TEs was first demonstrated by using in vitro TE cultures and confirmed in whole plants by using lignin monomer synthesis gene mutants that exhibit a reduction in TE lignification. The XP specific complementation of these mutants led to nearly completely rescuing the TE lignin reduction of the mutants. Experiments with in vitro TE cultures further revealed that non-TEs supply reactive oxygen species (ROS) to TEs and that ROS are required for TE post-mortem lignification. Non-TEs exhibit further an enlarged nucleus with increased DNA content, thus indicating that non-TEs are in fact endoreplicated xylem parenchyma (XP) cells. Microscopic analysis of the spatial distribution of lignin in in vitro TE cultures and whole plants revealed that lignification is restricted to TE SCWs in both protoxylem and metaxylem. These specific lignin deposition domains were found to be established by phenoloxidases, i.e. laccases and peroxidases. Laccases were cell-autonomously produced by developing TEs, indicating that the deposition domains are defined before PCD.
Altogether, these results highlight that the hydro-mineral sap conduction through TEs is enabled by the spatially and temporally controlled lignification of the SCW. Lignification occurs post-mortem by the supply of monomers and ROS from neighboring XP cells and is restricted to specific deposition domains, defined by the pre-mortem production of phenoloxidases.