Interspecific differences in photosynthetic efficiency and spectral reflectance in two Umbilicaria species from Svalbard during controlled desiccation

This study aimed to evaluate the effective photosynthetic quantum yield ( Phi PSII) and the Photochemical Reflectance Index (PRI) for assessment of photosynthetic performance of two Umbilicaria lichens during gradual desiccation of their thalli. U. cylindrica and U. decussata exhibited curvilinear relationship (S-shape curve) of decreasing Phi PSII values with decreasing water potential (WP) of thalli. During initial phase of desiccation (WP from 0 to -10 MPa), no decrease of Phi PSII was apparent, further desiccation (WP from -10 to -20 MPa) led to fast Phi PSII decrease from 0.6 to 0.1 indicating strong inhibition of photosynthetic processes. Critical WP at which photosythetic processes are fully inhibited was found bellow -25 MPa in both lichen species. Photochemical Reflectance Index (PRI) exhibited curvilinear increase with thalli desiccation (decreasing WP). At full thallus hydration, the PRI reached the value of -0.18 in both species. Under strong dehydration (WP from -20 to -30 MPa), however, U. cylindrica showed somewhat lower value (-0.04) than U.decussata (-0.02 MPa). PRI to WP relationship is discussed and compared to existing evidence from higher plants and poikilohydric organisms.Tato publikace je zaměřena na souběžné sledování indexu PRI a efektivního kvantového výtěžku fyotoyntézy během vysychání stélek dvou druhů lišejníků rodu Umbilicaria ze souostroví Špicberky (Svalbard). Byl zjištěno, že PRI s postupujícím vysycháním roste, zatímco u listů vyšších rostlin klesá.This study aimed to evaluate the effective photosynthetic quantum yield (Phi PSII) and the Photochemical Reflectance Index (PRI) for assessment of photosynthetic performance of two Umbilicaria lichens during gradual desiccation of their thalli. U. cylindrica and U. decussata exhibited curvilinear relationship (S-shape curve) of decreasing Phi PSII values with decreasing water potential (WP) of thalli. During initial phase of desiccation (WP from 0 to -10 MPa), no decrease of Phi PSII was apparent, further desiccation (WP from -10 to -20 MPa) led to fast Phi PSII decrease from 0.6 to 0.1 indicating strong inhibition of photosynthetic processes. Critical WP at which photosythetic processes are fully inhibited was found bellow -25 MPa in both lichen species. Photochemical Reflectance Index (PRI) exhibited curvilinear increase with thalli desiccation (decreasing WP). At full thallus hydration, the PRI reached the value of -0.18 in both species. Under strong dehydration (WP from -20 to -30 MPa), however, U. cylindrica showed somewhat lower value (-0.04) than U.decussata (-0.02 MPa). PRI to WP relationship is discussed and compared to existing evidence from higher plants and poikilohydric organisms

An improved method for the visualization of conductive vessels in Arabidopsis thaliana inflorescence stems

Dye perfusion is commonly used for the identification of conductive elements important for the study of xylem development as well as precise hydraulic estimations. The tiny size of inflorescence stems, the small amount of vessels in close arrangement, and high hydraulic resistivity delimit the use of the method for quantification of the water conductivity of Arabidopsis thaliana, one of the recently most extensively used plant models. Here, we present an extensive adjustment to the method in order to reliably identify individual functional (conductive) vessels. Segments of inflorescence stems were sealed in silicone tubes to prevent damage and perfused with a dye solution. Our results showed that dyes often used for staining functional xylem elements (safranin, fuchsine, toluidine blue) failed with Arabidopsis. In contrast, Fluorescent Brightener 28 dye solution perfused through segments stained secondary cell walls of functional vessels, which were clearly distinguishable in native cross sections. When compared to identification based on the degree of development of secondary cell walls, identification with the help of dye perfusion revealed a significantly lower number of functional vessels and values of theoretical hydraulic conductivity. We found that lignified but not yet functional vessels form a substantial portion of the xylem in apical and basal segments of Arabidopsis and, thus, significantly affect the analyzed functional parameters of xylem. The presented methodology enables reliable identification of individual functional vessels, allowing thus estimations of hydraulic conductivities to be improved, size distributions and vessel diameters to be refined, and data variability generally to be reduced

Interspecific differences in photosynthetic efficiency and spectral reflectance in two Umbilicaria species from Svalbard during controlled desiccation

This study aimed to evaluate the effective photosynthetic quantum yield (FPSII) and the Photochemical Reflectance Index (PRI) for assessment of photosynthetic performance of two Umbilicaria lichens during gradual desiccation of their thalli. U. cylindrica andU. decussata exhibited curvilinear relationship (S-shape curve) of decreasing FPSII values with decreasing water potential (WP) of thalli. During initial phase of desiccation (WP from 0 to -10 MPa), no decrease of FPSII was apparent, further desiccation (WP from -10 to -20 MPa) led to fast FPSII decrease from 0.6 to 0.1 indicating strong inhibition of photosynthetic processes. Critical WP at which photosythetic processes are fully inhibited was found bellow -25 MPa in both lichen species. Photochemical Reflectance Index (PRI) exhibited curvilinear increase with thalli desiccation (decreasing WP). At full thallus hydration, the PRI reached the value of -0.18 in both species. Under strong dehydration (WP from -20 to -30 MPa), however, U. cylindrica showed somewhat lower value (-0.04) than U.decussata (-0.02 MPa). PRI to WP relationship is discussed and compared to existing evidence from higher plants and poikilohydric organisms

Interspecific differences in photosynthetic efficiency and spectral reflectance in two Umbilicaria species from Svalbard during controlled desiccation

This study aimed to evaluate the effective photosynthetic quantum yield (FPSII) and the Photochemical Reflectance Index (PRI) for assessment of photosynthetic performance of two Umbilicaria lichens during gradual desiccation of their thalli. U. cylindrica andU. decussata exhibited curvilinear relationship (S-shape curve) of decreasing FPSII values with decreasing water potential (WP) of thalli. During initial phase of desiccation (WP from 0 to -10 MPa), no decrease of FPSII was apparent, further desiccation (WP from -10 to -20 MPa) led to fast FPSII decrease from 0.6 to 0.1 indicating strong inhibition of photosynthetic processes. Critical WP at which photosythetic processes are fully inhibited was found bellow -25 MPa in both lichen species. Photochemical Reflectance Index (PRI) exhibited curvilinear increase with thalli desiccation (decreasing WP). At full thallus hydration, the PRI reached the value of -0.18 in both species. Under strong dehydration (WP from -20 to -30 MPa), however, U. cylindrica showed somewhat lower value (-0.04) than U.decussata (-0.02 MPa). PRI to WP relationship is discussed and compared to existing evidence from higher plants and poikilohydric organisms

A heterobimetallic copper–titanium oxo cluster with a new structural motif

ABSTRACT: Mixed-metal oxo clusters Cu(4)Ti(5)O(6)(OOCR)(16) (OOCR = methacrylate, propionate) were obtained by reaction of titanium alkoxides and copper carboxylates with propionic or methacrylic acid. GRAPHICAL ABSTRACT: [Image: see text

Preparation and modification of carboxylate-substituted metal oxo clusters

Anorganisch-organische Hybridmaterialien, in denen anorganische und organische Bestandsteile kovalent miteinander verbunden sind, zweite Klasse von Hybridmaterialien, stellen eine interessante Klasse von Materialien dar, mit sehr breiten Eigenschaften und Anwendungen. Durch die Verwendung von organisch modifizierten Metallalkoxiden, die an ihre Oberfläche polymerisierbare Liganden erhalten, lassen sich Hybridmaterialien herstellen.Im ersten Teil dieser Arbeit wurden organisch modifizierte Übergangsmetallcluster durch die Reaktion der entsprechenden Alkoxide mit Carbonsäuren hergestellt. Die Reaktion von Gemischen aus Titan und Yttriumalkoxiden mit Methacrylsäure führt zur Bildung von Mischcluster unterschiedlicher Zusammensetzung. Die Reaktion von Zr(OBu)4 mit Propion-, Essig- und Dimethylacrylsäure führte zur Bildung von Zirconium Oxo Clustern mit entsprechenden Liganden durch. In gleicher Form und Größe wie bei Zirconium Oxo Clustern wurde der Hafnium Oxo Cluster in der Reaktion von Hf(OBu)4 mit Essigsäure gebildet.Im zweiten Teil dieser Arbeit wurde versucht die polymerisierbaren Liganden an Metall Oxo Clustern zu reduzieren. Das wurde sowohl bei Hydrosilylierungsreaktionen als auch beim Austausch von an die Oberfläche gebundenen Liganden gegen andere Säuren untersucht. Abhängig vom molaren Verhältnis zwischen Clustern und freien Carbonsäuren wurden gemischte Oxo Cluster mit funktionalen und nicht-funktionalen Säuren erhalten. Durch Radikalcopolymerisation der Hafnium/Titan Cluster mit Methylmethacrylaten als organisches Monomer, wurden anorganisch-organische Hybridmaterialien hergestellt. Es wurden die thermische und mechanische Eigenschaften dieser Polymere untersucht.Inorganic-organic hybrid materials, in which the inorganic and organic part are connected by a covalent linkage, class II of hybrid materials, are an interesting class of materials with many possibilities, interesting properties and applications. In this work, metal oxide clusters substituted by polymerizable groups were investigated. Such clusters can be used as co-monomers in polymerization reactions. In the first part organically modified transition metal oxo clusters were prepared by reaction of metal alkoxides with functional and non-functional carboxylic acids. Upon reaction of titanium propoxide and yttrium 2-methoxyethoxide with methacrylic acid, three different mixed-metal clusters were obtained, depending on the titanium to yttrium alkoxide ratio: Ti4Y2O4(OMc)14(MeOCH2CH2OH)2, (OMc = methacrylate), Ti4Y2O4(OMc)14(MeOH)2 and Ti4Y2O4(OMc)12(OCH2CH2OMe)2(McOH)2. Reaction of mixtures of titanium propoxide and hafnium butoxide with methacrylic acid resulted in the formation of the mixed-metal cluster Hf4Ti4O6(OPr)4(OMc)16. Zr12O8(OH)8(OProp)24, (OProp = propionate), Zr12O8(OH)8(OAc)24 or Hf12O8(OH)8(OAc)24, (OAc = acetate), were prepared by the reaction of either zirconium butoxide or hafnium butoxide with propionic acid or acetic acid. Zr12O8(OH)8(OAcrMe2)24, (OAcrMe2 = dimethylacrylate), was prepared by the reaction of zirconium butoxide with dimethylacrylic acid. In the second part of the work, attempts were made to reduce the number of polymerizable ligands of metal oxo-clusters. This was tested by either hydrosilylation reaction of methacrylate-substituted cluster or by exchange of surface bonded ligands for other carboxylates. Depending on the molar ratio of clusters and carboxylic acid, oxo clusters with both functional and non-functional carboxylic acids were obtained, for example Zr6O4(OH)4(OMc)6(OIsob)6 or Zr6O4(OH)4(OMc)7(OOCEt)5.Free radical-iniciated polymerisation of Hf4Ti4O6(OPr)4(OMc)16 with methyl methacrylate, resulted in cluster-crosslinked hybrid materials.Both thermal stability and mechanical properties of the polymers were improved by the crosslinking.9