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Biochemical and physiological responses of Arabidopsis thaliana seedlings exposed to cadmium, copper and zinc
No full textArabidopsis thaliana L. is considered a model plant for many studies as its genomic sequence was completely identified and its mechanisms in genomic, transcriptomic and proteomic regulation are often similar to other plant species. Seedlings of A. thaliana were exposed to cadmium, copper and zinc at two different concentrations, chosen on the basis of the levels of heavy metals realistically found in contaminated soils. After 7 and 12 days of exposure to metals, applied separately or in different combinations, plant shoots and roots were sampled and analyzed. Microscopic analysis revealed that root morphology was strongly affected by metal exposure, both alone or in combination, if compared to control plants. The different growth patterns observed for shoots and roots were likely due to a different production and proportion of auxins and cytokinins, the two most important classes of phyto-hormones affecting cell expansion and proliferation, respectively. The levels of trans-zeatin, dehydrozeatin and indolacetic acid, as well as the ratio auxins/cytokinins, were different among the plants treated with the metals above, and the perturbation given by cadmium appeared to be significant. Preliminary data on phytochelatins, thiol peptide compounds mainly produced by plants and algae, indicate that they can play an important role in metal homeostasis and detoxification of A. thaliana
Homeostatic needs and toxicity of metals: characterization of phytochelatin synthase in the liverwort Marchantia polymorpha
No full textRECOVERY IN APPLE PLANTS INFECTED WITH THE Apple Proliferation Phytoplasmas: An Ultrastructural and Biochemical Study
No full textLocalization of hydrogen peroxide (H2O2) and the roles of peroxidases, malondialdehyde, and reduced glutathione in three apple cultivars were compared in healthy trees, trees infected with apple proliferation phytoplasma (APP), and trees that had recovered from the infection. In recovered apple trees, symptoms of the disease and the pathogen had disappeared from the canopy, but phytoplasmas remained in the roots. H2O2 was detected cytochemically by its reaction with cerium chloride to produce electron-dense deposits of cerium perhydroxides.H2O2 occurred in the plasmalemma of the phloem of leaves of recovered apple trees, but not in healthy or APP-infected leaves. In all cultivars, the peroxidase activity detected in tissue from APP-diseased trees was greater than or equal to that of tissue from recovered trees, which equaled or exceeded that of tissue from healthy trees, at two sampling times (May and September). In contrast, the glutathione content of leaves decreased in the reverse order. More malondialdehyde was observed in leaves from recovered trees than in leaves from healthy or APP-infected trees in three of six cultivar-date combinations; in the other three combinations, the malondialdehyde contents of leaves from healthy, infected, and recovered trees were not significantly different from one another. The results suggest that some components of the oxidant-scavenging system in recovered leaves are not very active, leading to an overproduction of H2O2 and, possibly, to a membrane lipid peroxidation.The production of H2O2 appears to be involved in counteracting pathogen virulence
Inducibility, tissue-specificity and product variation of three phytochelatin synthase homeologs from the cadmiumtolerant reed A. donax L.
No full textPhytochelatins (PC) are a family of Cys-rich oligopeptides constituting the main defence of plants against toxicity of heavy
metals and metalloids like cadmium and arsenic. PCs are non-ribosomally synthesized from glutathione by the enzyme
phytochelatin synthase (PCS). Dicotyledonous PCS have been characterized in detail, while much less information is
available on monocotyledonous ones. In this study, we characterized three different PCS genes from giant reed (Arundo
donax L.), a biomass/bionergy crop with remarkable tolerance to cadmium, to study the evolution of this trait in monocots.
Phylogenetic reconstruction with PCS genes from fully sequenced monocotyledonous genomes indicated that the three A.
donax PCS, AdPCS1-3, are most likely homeologs - resulting from lineage-specific whole-genome polyploidization.
AdPCS1-3 genes are tissue-specifically expressed, and AdPCS1 is expressed about 5 times more than AdPCS2 and
AdPCS3. All three genes displayed cadmium-responsive expression in roots, and coded for functional PCSs, as once
overexpressed in yeast they confer enhanced tolerance to cadmium stress. Overexpression of AdPCS1-3 in Arabidopsis
thaliana further confirmed the typical phenoytype associated to overexpression of functional PCS genes. Mass-spectral
analyses detected statistically significant differences in the amount and spectral feature of the PCs synthesized, with
AdPCS2 and AdPCS1 producing, respectively, the highest and lowest amount of total PCs in yeast cells. AdPCS1
synthesized the same amount of PC2, PC3 and PC4, while both AdPCS2 and AdPCS3 enzymes produced significantly
higher amounts of PC2 and PC3 compared to PC4.
Taken together, these results indicate that the genetic bases of A. donax high capability to tolerate the presence of heavy
metals is, at least in part, related to the high functional specialization of its PCS genes from a transcriptional as well as
enzymatic point of view. Thus, transcriptional neofunctionalization and specialization seems to have played a major role in
the evolution of Cd tolerance in A. donax
Retaining unlogged patches in Mediterranean oak forests may preserve threatened forest macrolichens
Full text linkForest management practices may heavily impact epiphytic (tree inhabiting)
organisms. Retaining tree patches and buffer strips in logged stands may contribute
to preserve ecosystem functioning and the vitality of epiphytic organisms
in managed forests. To test these statements, the threatened forest
macrolichen Lobaria pulmonaria (L.) Hoffm. was used as a model species,
since it is a “flag” indicator species of forest ecosystems with long ecological
continuity. To this purpose, photosynthetic performances, thallus anatomy and
water holding capacity (WHC) of samples of L. pulmonaria were investigated in
a logged mixed oak forest (Tuscany, Italy), confronting lichen thalli from retained-
forest patches and retained-isolated trees, 18 months after logging.
Compared with those of retained-forest patches, thalli on the trunks of retained-
isolated trees were thinner and showed lower vitality (as indicated by
the potential quantum yield of primary photochemistry – FV/FM and the index
of overall photosynthetic performance – PIABS), as well as lower water holding
capacity. In contrast, thalli from forest patches had performances comparable
to those of healthy samples from unlogged forests
Divergent patterns of metal/metalloid responsiveness and detoxification of two Medicago truncatula Gaertn. phytochelatin synthase genes
Full text linkIntracellular and extracellular thiol-peptides modulate the response of Marchantia polymorpha to physiological needs, excess, and starvation of zinc, copper, and iron
No full textThiol-peptides, such as glutathione and phytochelatins, are believed to play a crucial role in regulating metal micronutrient needs (in particular, copper, iron, and zinc), and in detoxifying their excessive amounts. This study provides insight into the mechanisms involved in detoxification, starvation, and physiological control of the aforesaid metals in the liverwort Marchantia polymorpha. The results show that the phytochelatin synthase activity in gametophytes of M. polymorpha is induced mainly by zinc, followed by copper, and iron. Interestingly, the amount of phytochelatins produced seems to be controlled by the enzyme activity, rather than by the expression level of its gene. Moreover, when gametophytes are deprived of zinc, copper, and iron, phytochelatin levels decrease, compared with normal nutrient supply. Phytochelatins and glutathione, on the other hand, appear to play a key role in detoxification of excess zinc, copper, and iron, particularly when these thiol-peptides are released extracellularly. This suggests a potential novel function for phytochelatins and glutathione as detoxifying compounds also in the extracellular environmen
Auxin accumulation and transport in Arabidopsis Thaliana (L.) Heynh adventitious roots are modified by cadmium and arsenic
No full textWater availability modifies tolerance to photo-oxidative pollutants in transplants of the lichen Flavoparmelia caperata
No full textThe hypothesis that a daily water supply allows a lichen to endure the negative effects of environmental concentrations of NOx and O3 was tested with a transplant experiment. Five groups (0, A–D) of Flavoparmelia caperata samples derived from the same thalli were used for destructive, pre-exposure measurements (0), or exposed for 5 weeks in the rural collection site (A), and in a urban site with high levels of NOx and O3 (B–D). Two groups (C, D) were daily watered half an hour before the daily peak of NOx (C), and O3 (D). The comparison between pre- and post-exposure measurements of stress biomarkers revealed that the different thallus hydration regime modified the pollution tolerance as well as the physiology of the exposed samples. The non-watered group B suffered an evident decrease in Fv/Fm and reduced glutathione, but increased ion leakage, whereas the watered groups C and D showed only decreased non-photosynthetic-quenching, possibly derived from NOx exposure. Ozone, which was hi
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