Effects of Heavy Metals and Arbuscular Mycorrhiza on the Leaf Proteome of a Selected Poplar Clone: A Time Course Analysis

Arbuscular mycorrhizal (AM) fungi establish a mutualistic symbiosis with the roots of most plant species. While receiving photosynthates, they improve the mineral nutrition of the plant and can also increase its tolerance towards some pollutants, like heavy metals. Although the fungal symbionts exclusively colonize the plant roots, some plant responses can be systemic. Therefore, in this work a clone of Populus alba L., previously selected for its tolerance to copper and zinc, was used to investigate the effects of the symbiosis with the AM fungus Glomus intraradices on the leaf protein expression. Poplar leaf samples were collected from plants maintained in a glasshouse on polluted (copper and zinc contaminated) or unpolluted soil, after four, six and sixteen months of growth. For each harvest, about 450 proteins were reproducibly separated on 2DE maps. At the first harvest the most relevant effect on protein modulation was exerted by the AM fungi, at the second one by the metals, and at the last one by both treatments. This work demonstrates how importantly the time of sampling affects the proteome responses in perennial plants. In addition, it underlines the ability of a proteomic approach, targeted on protein identification, to depict changes in a specific pattern of protein expression, while being still far from elucidating the biological function of each protein

Ion homeostasis in the Chloroplast

peer reviewedThe chloroplast is an organelle of high demand for macro- and micro-nutrient ions, which are required for the maintenance of the photosynthetic process. To avoid deficiency while preventing excess, homeostasis mechanisms must be tightly regulated. Here, we describe the needs for nutrient ions in the chloroplast and briefly highlight their functions in the chloroplastidial metabolism. We further discuss the impact of nutrient deficiency on chloroplasts and the acclimation mechanisms that evolved to preserve the photosynthetic apparatus. We finally present what is known about import and export mechanisms for these ions. Whenever possible, a comparison between cyanobacteria, algae and plants is provided to add an evolutionary perspective to the description of ion homeostasis mechanisms in photosynthesis

Analysis of non-structural carbohydrates and xylem anatomy of leaf petioles offers new insights in the drought response of two grapevine cultivars

In grapevine, the anatomy of xylem conduits and the non-structural carbohydrates (NSCs) content of the associated living parenchyma are expected to influence water transport under water limitation. In fact, both NSC and xylem features play a role in plant recovery from drought stress. We evaluated these traits in petioles of Cabernet Sauvignon (CS) and Syrah (SY) cultivars during water stress (WS) and recovery. In CS, the stress response was associated to NSC consumption, supporting the hypothesis that starch mobilization is related to an increased supply of maltose and sucrose, putatively involved in drought stress responses at the xylem level. In contrast, in SY, the WS-induced increase in the latter soluble NSCs was maintained even 2 days after re-watering, suggesting a different pattern of utilization of NSC resources. Interestingly, the anatomical analysis revealed that conduits are constitutively wider in SY in well-watered (WW) plants, and that water stress led to the production of narrower conduits only in this cultivar

Effect of humic acids on phosphate level and energetic metabolism of tobacco BY-2 suspension cell cultures

To investigate the role of natural humic substances on plant cell phosphate level and metabolism, tobacco BY-2 suspension cell cultures were grown in the presence of humic samples of different chemical composition: soil humic acid and its three size-fractions (I-III) separated by High Pressure Size Exclusion Chromatography. The humic samples were characterized by CPMAS-NMR spectroscopy and on-line pyrolysis-gas chromatography-mass spectrometry. Suspension cell cultures, after 7 days of incubation, were facing Pi starvation. The fraction III, the most hydrophilic and smallest in molecular size among humic samples, induced a partial relief from Pi starvation, increasing total cell phosphate amount, ATP and glucose-6-phosphate levels, as well as the activity of secreted acid phosphatases. Furthermore, fraction III induced a decrease of KCN-insensitive respiration, evaluated in both suspension cells and isolated mitochondria. The low amount of acidic groups in fraction III excluded that its observed effect in relieving cells from Pi deficiency may be attributed to a partial replacement of the chelating ability of secreted acids (mainly citric and malic acids) in releasing Pi from metal-phosphate complexes. The molecular characteristics of fraction III are conducive to a flexible conformational structure due to hydrophilic domains, which are still contoured by hydrophobic moieties such as alkyl and aromatic compounds. Such flexible molecular associations may induce an efficient release of Pi from organic sources (e.g. nucleic acids), released in the media by damaged or dead cells, exerting a sort of positive effect on either the production or activity of extracellular Pi hydrolytic enzymes. This work shows that only by combining advanced molecular characterization of natural humic molecules with their effect on plant cells, it is possible to formulate sound hypotheses for structure-activity relationships