Long-term mannitol-induced osmotic stress leads to stomatal closure, carbohydrate accumulation and changes in leaf elasticity in Phaselous vulgaris leaves

The effect of long-term osmotic stress was investigated in leaves of two common bean lines, with contrasting tolerance: Flamingo (tolerant) and coco blanc (sensitive). Water relations, organic solute, ion accumulation and amino acids content as well as osmotic adjustment (OA) were studied during an extended exposure to osmotic stress. Osmotic stress was applied by means of 50 mM mannitol for 15 days. At the end of the stress period, both osmotic potential at full turgor (Ψ100) and at turgor loss point (Ψ0) decreased significantly in stressed plants compared with the control. The decrease being greater in the sensitive line, showed a greater OA compared with flamingo. Sugars contents increased in stressed plants and seem to be the major components of osmotic adjustment in stressed common bean leaves. The increase was more marked in coco blanc. Osmotic stress tolerance could thus not be associated with higher OA. The possible role of decreased leaf cell elasticity (εmax) is discussed in relation to osmotic stress tolerance in this species.Key words: Common bean, carbohydrate accumulation, growth, osmotic stress, osmotic adjustment, P-V curve, water relations

Absolute quantification of Medicago truncatula sucrose synthase isoforms and N-metabolism enzymes in symbiotic root nodules and the detection of novel nodule phosphoproteins by mass spectrometry

Mass spectrometry (MS) has become increasingly important for tissue specific protein quantification at the isoform level, as well as for the analysis of protein post-translational regulation mechanisms and turnover rates. Thanks to the development of high accuracy mass spectrometers, peptide sequencing without prior knowledge of the amino acid sequence—de novo sequencing—can be performed. In this work, absolute quantification of a set of key enzymes involved in carbon and nitrogen metabolism in Medicago truncatula ‘Jemalong A17’ root nodules is presented. Among them, sucrose synthase (SuSy; EC 2.4.1.13), one of the central enzymes in sucrose cleavage in root nodules, has been further characterized and the relative phosphorylation state of the three most abundant isoforms has been quantified. De novo sequencing provided sequence information of a so far unidentified peptide, most probably belonging to SuSy2, the second most abundant isoform in M. truncatula root nodules. TiO2-phosphopeptide enrichment led to the identification of not only a phosphorylation site at Ser11 in SuSy1, but also of several novel phosphorylation sites present in other root nodule proteins such as alkaline invertase (AI; EC 3.2.1.26) and an RNA-binding protein

Session 17 Ecophysiology

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Dynamics in poly(n-alkyl methacrylates): A neutron scattering, calorimetric, and dielectric study

13 páginas, 15 figuras, 4 tablas.-- El pdf del artículo es la versión post-print.Combining neutron diffraction, neutron spin echo, differential scanning calorimetry, and dielectric spectroscopy, we have investigated the structure and dynamics of poly(n-butyl methacrylate) (PBMA) and poly(n-hexyl methacrylate) (PHMA). Signatures of the occurrence of a glass transition associated with the freezing of the intermolecular correlations within alkyl nanodomains are present in the structural data. Exploiting isotopic labeling, neutron scattering has revealed collective dynamics at the main-chain and side-group levels for both polymers and the self-motions of hydrogen atoms in the side groups of PHMA, adding valuable microscopic information to comprehensive relaxation maps and putting the relaxation results into a perspective. Moreover, we find exotic dynamical behavior for the side groups, characterized by extremely stretched (nearly logarithmic-like) decays of the correlation functions. For PHMA, a complete dynamical decoupling of side-group dynamics from the main-chain motions is found. The side groups of this polymer show an extremely “strong” temperature dependence of the structural relaxation time and much faster characteristic times for self than collective motions. The analogies found between the self-motions of the side-group H atoms in PHMA and the γ-relaxation process in semicrystalline polyethylene (PE) strengthen the picture of confined PE-like dynamics within alkyl nanodomains. We discuss possible origins for the observed phenomenology.This research project has been supported by the European Commission NoE SoftComp, Contract NMP3-CT-2004-502235, the “Donostia International Physics Center”. A.A. and J.C. acknowledge support from the projects MAT2007-63681, IT-436-07 (GV), and the Spanish Ministerio de Educacion y Ciencia (Grant CSD2006-53).Peer reviewe

A novel biosensor to monitor proline in pea root exudates and nodules under osmotic stress and recovery

Background and aims: Plant and bacteria are able to synthesise proline, which acts as a compound to counteract the negative effects of osmotic stresses. Most methodologies rely on the extraction of compounds using destructive methods. This work describes a new proline biosensor that allows the monitoring of proline levels in a non-invasive manner in root exudates and nodules of legume plants. Methods: The proline biosensor was constructed by cloning the promoter region of pRL120553, a gene with high levels of induction in the presence of proline, in front of the lux cassette in Rhizobium leguminosarum bv. viciae. Results: Free-living assays show that the proline biosensor is sensitive and specific for proline. Proline was detected in both root exudates and nodules of pea plants. The luminescence detected in bacteroids did not show variations during osmotic stress treatments, but significantly increased during recovery. Conclusions: This biosensor is a useful tool for the in vivo monitoring of proline levels in root exudates and bacteroids of symbiotic root nodules, and it contributes to our understanding of the metabolic exchange occurring in nodules under abiotic stress conditions.</p

Dynamics in poly(n-alkyl methacrylates): A neutron scattering, calorimetric and dielectric study

Combining neutron diffraction, neutron spin echo, differential scanning calorimetry, and dielectric spectroscopy, we have investigated the structure and dynamics of poly(n-butyl methacrylate) (PBMA) and poly(n-hexyl methacrylate) (PHMA). Signatures of the occurrence of a glass transition associated with the freezing of the intermolecular correlations within alkyl nanodomains are present in the structural data. Exploiting isotopic labeling, neutron scattering has revealed collective dynamics at the main-chain and side-group levels for both polymers and the self-motions of hydrogen atoms in the side groups of PHMA, adding valuable microscopic information to comprehensive relaxation maps and putting the relaxation results into a perspective. Moreover, we find exotic dynamical behavior for the side groups, characterized by extremely stretched (nearly logarithmic-like) decays of the correlation functions. For PHMA, a complete dynamical decoupling of side-group dynamics from the main-chain motions is found. The side groups of this polymer show an extremely "strong" temperature dependence of the structural relaxation time and much faster characteristic times for self than collective motions. The analogies found between the self-motions of the side-group H atoms in PHMA and the gamma-relaxation process in semicrystalline polyethylene (PE) strengthen the picture of confined PE-like dynamics within alkyl nanodomains. We discuss possible origins for the observed phenomenology