Arleta Małecka

Accumulation and detoxification of lead ions in legumes.

This study focuses on lead accumulation in roots, stems and leaves of three plant species of the Fabacea family: Vicia faba, Pisum sativum and Phaseolus vulgaris grown hydroponically in a medium supplemented with 1 mM concentration of lead. The largest amount of lead, up to 75 mg Pb/g dry weight, was accumulated in roots of P. vulgaris. The highest rate of Pb ions uptake from the medium took place during the first 10 h of incubation with lead and after 96 h of incubation lead content in the medium decreased by half. Thus, it was suggested that P. vulgaris could be used in rhizofiltration--the use of plant roots to absorb pollutants from water contaminated with lead. At the same time we studied the influence of lead on acid soluble thiol, glutathione, homoglutathione contents and the synthesis of phyto- and homophytochelatins in roots of V. faba, P. sativum and P. vulgaris grown hydroponically. Activation of the detoxicative-phytochelatin system was observed in the cytosol of root cells of the tested plants. This system was composed of phytochelatins (PCs) in roots of V. faba, homophytochelatins (hPCs) in P. vulgaris roots and both PCs and hPCs in P. sativum roots. The total content of PCs and hPCs in roots of P. sativum was very high and reached around 4800 (expressed in nmol SH x g(-1)FW) and induction of their synthesis occurred after only 2 h of treatment with 1 mM Pb.

The production, localization and spreading of reactive oxygen species contributes to the low vitality of long-term stored common beech (Fagus sylvatica L.) seeds.

The common beech (Fagus sylvatica L.) is propagated by seeds, but the seed set is irregular with five to ten years in between crops. It is therefore necessary to store the seeds. However, beech seeds lose germinability during long-term storage. In this study, beech seeds were stored at -10°C under controlled conditions for 2, 5, 8, 11 and 13 years. Our results show that beech seeds lose germinability during storage in proportion to the duration of storage. The decrease in germinability correlated with increased electrolyte leakage and accumulation of superoxide anion radicals, hydrogen peroxide and hydroxyl radicals. Furthermore, a strong positive correlation was observed among the releases of superoxide anion radicals, hydrogen peroxide and hydroxyl radicals. In situ localization showed that superoxide anion radicals and hydrogen peroxide were first detectable in root cap cells. When the seed storage time was extended, the reactive oxygen species fluorescence expanded to more areas of the radicle, reaching the root apical meristem. A storage time-dependent decrease in catalase activity, observed in both embryonic axes and cotyledons, was also positively correlated with germinability. DNA fragmentation was observed in beech seeds during storage and occurred predominantly in embryonic axes stored for 5 years and more. Altogether, these results suggest that the loss of germinability in beech seeds during long-term storage depends on several factors, including strong of reactive oxygen species accumulation accompanied by reduced catalase activity as well as membrane injury and DNA alternations, which may be aging-related and ROS-derived. We suggest that the accumulating reactive oxygen species that spread to the root apical meristem are key factors that affect seed germinability after long-term storage.

Rhizoremediation of Diesel-Contaminated Soil with Two Rapeseed Varieties and Petroleum degraders Reveals Different Responses of the Plant Defense Mechanisms

Plant-assisted bioremediation (rhizoremediation) stands out as a potential tool to inactivate or completely remove xenobiotics from the polluted environment. Therefore, it is of key importance to find an adequate combination of plant species and microorganisms that together enhance the clean-up process. To understand the response of plants upon bioaugmentation, the antioxidative and detoxification system was analyzed in high and low erucic acid rapeseed varieties (HEAR and LEAR, respectively), after 8 weeks of their treatment with petroleum degraders and 6000 mg diesel oil/kg dry soil. The oxidative stress was enhanced in LEAR being exposed to sole diesel oil, in comparison with HEAR. However, when LEAR plants were additionally inoculated with bacteria, suppression of total catalase (CAT) and ascorbate peroxidase (APX) activity were observed. Interestingly, glutathione transferase (GST) activity was found in these plants at a much higher level than in HEAR, which correlated with a more efficient diesel removal performed by LEAR in the polluted soil and upon bioaugmentation. A distinct profile of polycyclic aromatic hydrocarbons (PAH) was detected in leaves of these plants. Neither LEAR nor HEAR experienced any changes in the photosynthetic capacity upon diesel pollution and presence of petroleum degraders, which supports the usefulness of rhizoremediation with rapeseed.

From Accumulation to Degradation: Reprogramming Polyamine Metabolism Facilitates Dark-Induced Senescence in Barley Leaf Cells

The aim of this study was to analyze whether polyamine (PA) metabolism is involved in dark-induced Hordeum vulgare L. ‘Nagrad’ leaf senescence. In the cell, the titer of PAs is relatively constant and is carefully controlled. Senescence-dependent increases in the titer of the free PAs putrescine, spermidine, and spermine occurred when the process was induced, accompanied by the formation of putrescine conjugates. The addition of the anti-senescing agent cytokinin, which delays senescence, to dark-incubated leaves slowed the senescence-dependent PA accumulation. A feature of the senescence process was initial accumulation of PAs at the beginning of the process and their subsequent decrease during the later stages. Indeed, the process was accompanied by both enhanced expression of PA biosynthesis and catabolism genes and an increase in the activity of enzymes involved in the two metabolic pathways. To confirm whether the capacity of the plant to control senescence might be linked to PA, chlorophyll fluorescence parameters, and leaf nitrogen status in senescing barley leaves were measured after PA catabolism inhibition and exogenously applied γ-aminobutyric acid (GABA). The results obtained by blocking putrescine oxidation showed that the senescence process was accelerated. However, when the inhibitor was applied together with GABA, senescence continued without disruption. On the other hand, inhibition of spermidine and spermine oxidation delayed the process. It could be concluded that in dark-induced leaf senescence, the initial accumulation of PAs leads to facilitating their catabolism. Putrescine supports senescence through GABA production and spermidine/spermine supports senescence-dependent degradation processes, is verified by H2O2 generation.

Effects of binary metal combinations on zinc, copper, cadmium and lead uptake and distribution in Brassica juncea

The interaction between lead, copper, cadmium and zinc in their binary combinations was investigated in Indian mustard seedlings (Brassica juncea L. var. Malopolska). Fourteen-days-old seedlings were treated with Pb(NO3)2, CuSO4, CdCl2, ZnSO4 at 50μmol of metal ion concentration and at 25μmol of each metal ion in combinations. Metal combinations were generally more inhibiting in terms of biomass production. This inhibiting effect followed an order: Cu+Cd>Cu+Zn, Cd+Pb>Cu+Pb>Zn+Pb, Cu>Cd>Zn>Zn+Cd>Pb. We observed synergistic and antagonistic effects of metal uptake in binary metal treatments, suggesting metal crosstalk at the plant uptake site. Metal content in plant tissues varied among different combinations. The metal concentrations followed an order of Pb>Cu>Zn>Cd in roots, Zn>Cu>Pb>Cd in the stem and Zn>Cu>Cd>Pb in leaves. Presence of metals altered the distribution of micronutrients (Cu, Zn) in plants: Cu concentration was lowered in roots and leaves and increased in stems; Zn content was increased in plants, with stems having up to 4 or 5 times more Zn than in control plants.

High Peroxide Level May Be a Characteristic Trait of a Hyperaccumulator

Under various abiotic stresses, plants overproduce reactive oxygen species (ROS) such as superoxide anion (O2•−), hydroxyl radical (OH•), and hydrogen peroxide (H2O2). When in excess, these highly reactive molecules cause oxidative stress, thus damaging proteins, lipids, and DNA. Therefore, plants evolved an enzymatic defense machinery that involves such enzymes as superoxide dismutase (SOD), catalase (CAT), and ascorbate peroxidase (APOX). Various plant families, species and even specimens differ in their ability to withstand the abiotic stress. A study has been undertaken to assess the differences in response to trace metals between two species: a resistant hyperaccumulator Indiana mustard (Brassica juncea) and a metal-sensitive pea (Pisum sativum). We observed that trace elements (Cu, Zn, Cd, Pb) changed the activity of antioxidative enzymes (SOD, APOX, CAT) and the rate of ROS generation. However, in the control plants and at a point 0′ of the treatment, we have noticed a large disproportion in the hydrogen peroxide level, with B. juncea maintaining naturally higher H2O2 level (up to 40 times higher). We believe that this may be a distinguishing trait common to plants being resistant to oxidative stress.