Structure, ultrastructure and cation accumulation in quinoa epidermal bladder cell complex under high saline stress.

Quinoa is a facultative halophyte with excellent tolerance to salinity. In this study, the epidermal bladder cell complex (EBCc) of quinoa leaves was studied to determine their cellular characteristics and involvement in salt tolerance. We used light microscopy, confocal RAMAN microscopy, confocal fluorescence microscopy, transmission electron microscopy, and environmental scanning electron microscopy complemented by energy dispersive X-ray analysis. Ionic content was quantified with flame atomic absorption spectroscopy and with flame emission photometry. Results show that: (i) the number of EBCcs remains constant but their density and area vary with leaf age; (ii) stalk cells store lipids and exhibit thick walls, bladder cells present carotenes in small vesicles, oxalate crystals in vacuoles and lignin in their walls and both stalk and bladder cells have cuticles that differ in wax and cutin content; (iii) chloroplasts containing starch can be found on both stalk and bladder cells, and the latter also presents grana; (iv) plasmodesmata are observed between the stalk cell and the bladder cell, and between the epidermal cell and the stalk cell, and ectodesmata-like structures are observed on the bladder cell. Under high salinity conditions, (v) there is a clear tendency to accumulate greater amounts of K+ with respect to Na+ in the bladder cell; (vi) stalk cells accumulate similar amounts of K+ and Na+; (vii) Na+ accumulates mainly in the medullary parenchyma of the stem. These results add knowledge about the structure, content, and role of EBCc under salt stress, and surprisingly present the parenchyma of the stem as the main area of Na+ accumulation.

Willow seedlings from photooxidized seeds accelerate cotyledon death and anticipate first leaf emergence: a histological and biochemical study following germination.

In willow seeds, photooxidative damage is mainly restricted to the outer cotyledonary tissues, significantly reducing normal germination. Here we analyzed the damage generated in cotyledonary tissues and investigated whether the increase in reactive oxygen species (ROS) generation in seedlings from photooxidized seeds can affect the morphogenetic capacity of the shoot apical meristem. Seeds were photooxidized under different light intensities and the evolution of the damage during seedling growth was studied by light and transmission electron microscopies. The level of lipid peroxidation and changes in antioxidant capacity were measured following the time course of superoxide dismutase, catalase, ascorbate peroxidase and guaiacol peroxidase enzyme activities, and the effect of photooxidative stress on the genesis of new leaf primordia and lateral roots was examined. Early and active endocytosis and autophagy, changes in chloroplast morphology, as well as the accumulation and diffusion of ROS all play important roles in the early cell death observed in cotyledonary tissues. Following germination, seedlings from photooxidized seeds anticipated the emergence of first leaves, which complemented the altered functionality of the damaged cotyledons.

Fluctuation of oxidative stress indicators in Salix nigra seeds during priming.

Salix nigra seeds subjected to increased humidification show a decrease in normal germination (NG) during early imbibition followed by a recovery in that parameter at increasing imbibition times. Since photo-oxidized seeds contain high levels of reactive oxygen species (ROS), it is possible to infer that the atypical decrease in NG is a consequence of a higher ROS mobilization at early imbibition and the subsequent recovery from an increase in antioxidant activity. In this study, several oxidative stress indicators were evaluated in photo-oxidized seeds subjected to priming. ROS production was studied using electronic spin resonance spectroscopy, spontaneous chemiluminescence (SCL), spectrophotometry (with XTT), and histochemical (with DAB and NBT) and cytochemical (with CeCl(3)) techniques. Four indicators of molecular damage were monitored: lipid peroxidation, pigment destruction, protein oxidation, and membrane integrity. Antioxidant activity was evaluated by changes in the enzymes SOD, CAT, APX, and POX. The results revealed that the decrease in NG at the beginning of priming occurs by an oxidative burst, as determined by increases in both SCL and superoxide anion radical (O2(·-)) Such oxidative burst generates lipid peroxidation, protein oxidation, and a decrease in both pigment content and enzyme activities. With increasing hydration, damages are progressively reversed and NG restored, which coincides with the increased activity of antioxidant defences. It is proposed that these novel observations regarding the occurrence of an oxidative burst are related to the high basal ROS levels and the high membrane content retained in the mature embryo tissues.

Chronic toxicity, bioavailability and bioaccumulation of Zn, Cu and Pb in Lactuca sativa exposed to waste from an abandoned gold mine.

Abandoned mines with untreated waste cause environmental pollution. The complex mixture of mining waste includes high metal content, anthropogenic chemicals and sterile rocks. Adverse effects of contaminated soils have been widely assessed by the use of plants. The aim of this study was to assess the chronic toxicity of a contaminated soil by waste from an abandoned gold mine on Lactuca sativa and its relationship with the bioavailability and bioaccumulation of Zn, Cu and Pb. Soil samples were taken from the site of mining waste stacking and a reference site in La Planta (Argentina). Contamination indices were calculated and acute and chronic exposures on L. sativa were carried out. Phytotoxicity indices, morphological and biochemical parameters, and concentrations of Zn, Cu and Pb in pseudo total and bioavailable soil fractions and in plant tissue were determined. Concentration- and time-dependent toxicity effects were observed, especially on plant width, fresh aerial biomass, leaf area and percentage of plants with completely necrotic aerial biomass. High levels of Zn (1453.3 ± 220.3 µg g-1) were found in plant tissue compared to Pb (277.2 ± 18.0 µg g-1) and Cu (255.3 ± 25.6 µg g-1). Toxicological endpoints correlated with metal uptake and mining waste concentration. In addition, bioaccumulation factors correlated with mobilisable and water soluble fractions. The concentration of Pb in aerial biomass surpassed the permissible concentrations in leaf vegetables, even at the reference site, indicating that lettuce crop consumption could be risky for the local population's health. This study demonstrated a strong relationship between metal bioavailability, toxicity endpoints and bioaccumulation, contributing with novel information to future ecotoxicological risk assessments and remediation plans.

Phytoextraction of Cu, Cd, Zn and As in four shrubs and trees growing on soil contaminated with mining waste.

Mining activity has degraded large extensions of soil and its waste is composed of metals, anthropogenic chemicals, and sterile rocks. The use of native species in the recovery of polluted soils improves the conditions for the emergence of other species, tending to a process of ecosystem restoration. The objective of this study was to evaluate the bioaccumulation of metal(loid)s in four species of native plants and the effect of their distribution and bioavailability in soil with waste from an abandoned gold mine. Soil samples were taken from two sites in La Planta, San Juan, Argentina: Site 1 and Site 2 (mining waste and reference soil, respectively). In Site 1, vegetative organ samples were taken from Larrea cuneifolia, Bulnesia retama, Plectrocarpa tetracantha, and Prosopis flexuosa. The concentration of metal(loid)s in soil from Site 1 were Zn > As > Cu > Cd, reaching values of 7123, 6516, 240 and 76 mg kg-1, respectively. The contamination indices were among the highest categories of contamination for all four metal(loid)s. The spatial interpolation analysis showed the effect of the vegetation as the lowest concentration of metal(loid)s were found in rhizospheric soil. The maximum concentrations of As, Cu, Cd and Zn found in vegetative organs were 371, 461, 28, and 1331 mg kg-1, respectively. L. cuneifolia and B. retama presented high concentrations of Cu and Zn. The most concentrated metal(loid)s in P. tetracantha and P. flexuosa were Zn, As and Cu. Cd was the least concentrated metal in all four species. The values of BAF and TF were greater than one for all four species. In conclusion, the different phytoextraction capacities and the adaptations to arid environments of these four species are an advantage for future phytoremediation strategies. Their application contributes to the ecological restoration and risk reduction, allowing the recovery of ecosystem services.

Effects of photooxidation on membrane integrity in Salix nigra seeds.

BACKGROUND AND AIMS: Salix nigra seeds are desiccation-tolerant, as are orthodox seeds, although in contrast to other orthodox seeds they lose viability in a few weeks at room temperature. They also differ in that the chloroplasts of the embryo tissues conserve their chlorophyll and endomembranes. The aim of this paper was to investigate the role of chlorophyll in seed deterioration. METHODS: Seeds were aged at different light intensities and atmospheric conditions. Mean germination time and normal and total germination were evaluated. The formation of free radicals was assessed using electronic spin resonance spectroscopy, and changes in the fatty acid composition from phospholipids, galactolipids and triglycerides using gas-liquid chromatography. Membrane integrity was studied with electronic spin resonance spin probe techniques, electrolyte leakage and transmission electron microscopy. KEY RESULTS: Light and oxygen played an important role in free-radical generation, causing a decrease in normal germination and an increase in mean germination time. Both indices were associated with a decrease in polyunsaturated fatty acids derived from membrane lipids as phospholipids and galactolipids. The detection of damage in thylakoid membranes and an increase in plasmalemma permeability were consistent with the decrease in both types of lipids. Triglycerides remained unchanged. Light-induced damage began in outermost tissues and spread inwards, decreasing normal germination. CONCLUSIONS: Salix nigra seeds were very susceptible to photooxidation. The thylakoid membranes appeared to be the first target of the photooxidative process since there were large decreases in galactolipids and both these lipids and the activated chlorophyll are contiguous in the structure of that membrane. Changes in normal germination and mean germination time could be explained by the deteriorative effects of oxidation.

The control of root growth by reactive oxygen species in Salix nigra Marsh. seedlings.

The production of reactive oxygen species (ROS) in specific regions of Salix seedlings roots seems essential for the normal growth of this organ. We examined the role of different ROS in the control of root development in Salix nigra seedlings, and explored possible mechanisms involved in the regulation of ROS generation and action. Root growth was not significantly affected by OH quenchers, while it was either partially or completely inhibited in the presence of H2O2 or O2·â» scavengers, respectively. O2·â» production was elevated in the root apex, particularly in the subapical meristem and protodermal zones. Apical O2·â» generation activity was correlated to a high level of either Cu/Zn superoxide dismutase protein as well as carbonylated proteins. While NADPH-oxidase (NOX) was probably the main source of O2·â» generation, the existence of other sources should not be discarded. O2·â» production was also high in root hairs during budding, but it markedly decreased when the hair began to actively elongate. Root hair formation increased in the presence of H2O2 scavengers, and was suppressed when H2O2 or peroxidase inhibitors were supplied. The negative effect of H2O2 was partially counteracted by a MAPKK inhibitor. Possible mechanisms of action of the different ROS in comparison with other plant model systems are discussed.

The ZFHX1A gene is differentially autoregulated by its isoforms.

The Zfhx1a gene expresses two different isoforms; the full length Zfhx1a-1 and a truncated isoform termed Zfhx1a-2 lacking the first exon. Deletion analysis of the Zfhx1a-1 promoter localized cell-specific repressors, and a proximal G-string that is critically required for transactivation. Transfection of Zfhx1a-1 cDNA, but not Zfhx1a-2, downregulates Zfhx1a-1 promoter activity. Mutation of an E2-box disrupted the binding of both Zfhx1a isoforms. Consistent with this, transfected Zfhx1a-1 does not regulate the transcriptional activity of the E-box mutated Zfhx1a-1 promoter. Competitive EMSAs and transfection assays show that Zfhx1a-2 can function as a dominant negative isoform since it is able to compete and displace Zfhx1a-1 from its binding site and overcome Zfhx1a-1 induced repression of the Zfhx1a-1 promoter in cells. Hence, the Zfhx1a-1 gene is autoregulated in part by negative feedback on its own promoter which is, in turn, modified by the availability of the negative dominant isoform Zfhx1a-2.