Plants as effective bioindicators for heavy metal pollution monitoring.

This study investigated the bioindicator potential of Amaranthus retroflexus L., Plantago lanceolata L., Rumex acetosa L., and Trifolium pratense L. including the use of Lolium multiflorum L. as a reference species, for heavy metal pollution monitoring, in particular Zinc (Zn), Cadmium (Cd), Nickel (Ni), and Lead (Pb). Controlled heavy metal contamination was applied through irrigation with metal nitrate solutions two levels of contamination (low and high). The study also focused on analyzing heavy metals concentration in plant tissues and related physiological responses. Distinct physiological responses to heavy metal stress were observed among the investigated species, highlighting unique variations in their reactions. Hydrogen peroxide, malondialdehyde content, and enzymatic activities emerged as reliable indicators of plant stress induced by heavy metal solutions. P. lanceolata displayed elevated Zn concentrations in both roots and leaves (3271 ± 337 and 4956 ± 82 mg kg-1). For Pb, L. multiflorum and P. lanceolata showed highest root concentrations (2964 ± 937 and 1605 ± 289 mg kg-1), while R. acetosa had higher leaf concentration (1957 ± 147 mg kg-1). For Ni, L. multiflorum had the highest root concentration (1148 ± 93 mg kg-1), and P. lanceolata exhibited the highest leaf concentration (2492 ± 28 mg kg-1). P. lanceolata consistently demonstrated the highest Cd concentrations in both roots (126 ± 21 mg kg-1) and leaves (163 ± 12 mg kg-1). These results provide valuable insights for selecting effective bioindicator species to establish control strategies for heavy metal pollution.

High-throughput method for Oxygen Consumption Rate measurement (OCR) in plant mitochondria.

BACKGROUND: Conventional methods to measure oxygen consumption, such as Clark-type electrodes, have limitations such as requiring a large amount of starting material. Moreover, commercially available kits for high-throughput methods are usually optimized for animal cells and mitochondria. Here, we present a novel method to measure the oxygen consumption rate using a high-throughput assay in isolated mitochondria of European beech seeds. To perform the measurements, we adapted the Agilent Seahorse XF Cell Mito Stress Test Kit protocol for measurements on plant mitochondria. RESULTS: The optimized protocol for OCR measurement of mitochondria isolated from beech seeds allowed the observation of storage period-dependent gradual decreases in non-phosphorylating respiration, phosphorylating respiration and maximal FCCP-stimulated respiration. The longer the seeds were stored, the greater the impairment of respiratory function. CONCLUSIONS: Thanks to this method it is possible to minimize the amount of plant material and conduct research to obtain information on the respiratory condition and activity of plant mitochondria, including the efficiency of oxidative phosphorylation and the maximum oxidative capacity of the respiratory chain. We demonstrated that the improved protocol is suitable for study of plant material.

Insight into the Phytoremediation Capability of Brassica juncea (v. Malopolska): Metal Accumulation and Antioxidant Enzyme Activity.

Metal hyperaccumulating plants should have extremely efficient defense mechanisms, enabling growth and development in a polluted environment. Brassica species are known to display hyperaccumulation capability. Brassica juncea (Indiana mustard) v. Malopolska plants were exposed to trace elements, i.e., cadmium (Cd), copper (Cu), lead (Pb), and zinc (Zn), at a concentration of 50 µM and were then harvested after 96 h for analysis. We observed a high index of tolerance (IT), higher than 90%, for all B. juncea plants treated with the four metals, and we showed that Cd, Cu, Pb, and Zn accumulation was higher in the above-ground parts than in the roots. We estimated the metal effects on the generation of reactive oxygen species (ROS) and the levels of protein oxidation, as well as on the activity and gene expression of antioxidant enzymes, including superoxide dismutase (SOD), catalase (CAT), and ascorbate peroxidase (APX). The obtained results indicate that organo-specific ROS generation was higher in plants exposed to essential metal elements (i.e., Cu and Zn), compared with non-essential ones (i.e., Cd and Pb), in conjunction with SOD, CAT, and APX activity and expression at the level of encoding mRNAs and existing proteins. In addition to the potential usefulness of B. juncea in the phytoremediation process, the data provide important information concerning plant response to the presence of trace metals.

Evaluation of P5CS and ProDH activity in Paulownia tomentosa (Steud.) as an indicator of oxidative changes induced by drought stress.

The aim of the study was to investigate changes in proline metabolism in seedlings of tree species during drought stress. One month old Paulownia tomentosa seedlings were exposed to moisture conditions at various levels (irrigation at 100, 75, 50 and 25% of field capacity), and then the material (leaves and roots) was collected three times at 10-day intervals. The activity of enzymes involved in proline metabolism was closely related to drought severity; however, proline content was not directly impacted. The activity of pyrroline-5-carboxylate synthetase (P5CS), which catalyzes proline biosynthesis, increased in response to hydrogen peroxide accumulation, which was correlated with soil moisture. In contrast, the activity of proline dehydrogenase (ProDH), which catalyzes proline catabolism, decreased. Compared to proline, the activity of these enzymes may be a more reliable biochemical marker of stress-induced oxidative changes. The content of proline is dependent on numerous additional factors, i.e., its degradation is an important alternative energy source. Moreover, we noted tissue-specific differences in this species, in which roots appeared to be proline biosynthesis sites and leaves appeared to be proline catabolism sites. Further research is needed to examine a broader view of proline metabolism as a cycle regulated by multiple mechanisms and differences between species.

The chances in the redox priming of nondormant recalcitrant seeds by spermidine.

The problems posed by seed sensitivity to desiccation and aging have motivated the development of various techniques for mitigating their detrimental effects. The redox priming of seeds in antioxidant solution to improve their postharvest performance is one of the approaches. Spermidine (Spd) was tested as an invigorating solution on nondormant recalcitrant (desiccation-sensitive) seeds of the silver maple (Acer saccharinum L.). The treatment resulted in an 8-10% increase in germination capacity in seeds subjected to mild and severe desiccation, while in aged seeds stored for 6 months, no significant change was observed. The cellular redox milieu, genetic stability, mitochondrial structure and function were investigated to provide information about the cellular targets of Spd activity. Spermidine improved the antioxidative capacity, especially the activity of catalase, and cellular membrane stability, protected genome integrity from oxidative damage and increased the efficiency of mitochondria. However, it also elicited a hydrogen peroxide burst. Therefore, it seems that redox priming in nondormant seeds that are highly sensitive to desiccation, although it positively affected desiccated seed performance, may not be a simple solution to reinvigorate stored seeds with a low-efficiency antioxidant system.

Relationship between mitochondrial changes and seed aging as a limitation of viability for the storage of beech seed (Fagus sylvatica L.).

Aging is one of the most fundamental biological processes occurring in all forms of eukaryotic life. Beech trees (Fagus sylvatica L.) produce seeds in intervals of 5-10 years. Its yearly seed yield is usually very low, so there is a need for long-term seed storage to enable propagation of this species upon demand. Seeds for sowing must be of high quality but they are not easy to store without viability loss. Understanding the mechanism responsible for seed aging is therefore very important. We observed the generation of reactive oxygen species (ROS) in mitochondria of embryonic axes and cotyledons of beech seeds during natural aging. The presence of ROS led to changes in compromised mitochondrial membrane integrity and in mitochondrial metabolism and morphology. In this study, we pointed to the involvement of mitochondria in the natural aging process of beech seeds, but the molecular mechanisms underlying this involvement are still unknown.

Activation of antioxidative and detoxificative systems in Brassica juncea L. plants against the toxicity of heavy metals.

Plant metal hyperaccumulators, to which Brassica juncea belongs, must have very efficient defence mechanisms that enable growth and development in an environment polluted with various heavy metals. B. juncea (Indiana mustard) v. Malopolska was exposed to the activity of trace elements such as cadmium (Cd), copper (Cu), lead (Pb), and zinc (Zn) in combinations: CuPb, CuCd, CuZn, PbCd, PbZn, and ZnCd in a concentration of 25 µM each for 96 h during control cultivation. We observed a clear tendency for metal uptake and accumulation in above-ground parts which is characteristic of hyperaccumulators. The combinations of CuCd, CuZn, and PbCd inhibited the development of the seedlings the most. The used metal combinations increased the levels of reactive oxygen species (ROS) such as: hydrogen peroxide (H2O2), superoxide anion (O2.-) and oxidized proteins in B. juncea organs, generating oxidative stress conditions in the cells. We determined the level of transcription of the respective defence proteins of the detoxification and antioxidant systems. We have shown that in the first 24 h of stress condiction, activation of glutamylcysteine-γ synthetase (yECS) and glutathione reductase (GR1) enzymes related to the detoxification of heavy metals is important for B. juncea plants. In addition, the data provide important information on how plants respond to the presence of heavy metals in the first days of stress conditions.

Combined use of companion planting and PGPR for the assisted phytoextraction of trace metals (Zn, Pb, Cd).

Biomass production and metal accumulation in plant tissue (bioconcentration) are two critical factors limiting the phytoextraction rate. Metal translocation to aboveground organs should be accounted for as the third most important factor, as harvesting of the plant roots is usually economically disadvantageous. These three parameters could be potentially increased with the use of companion planting, a well-known agricultural technique, and inoculation with plant growth-promoting bacteria (PGPB). The aim of the study was to determine whether intercropping and inoculation with endophytic PGPB (Burkholderia phytofirmans PsJNT) can increase the efficiency of phytoextraction of Zn, Pb, and Cd. The study was conducted on Brassica juncea (L.) Czern. "Malopolska" grown in a monoculture or co-planted with Zea mays L. "Codimon" and Medicago sativa L. "Sanditi." Results show that companion planting and inoculation with rhizobacteria can increase the efficiency of metal phytoextraction, mainly by increasing the yield of dry biomass and the survival rate of plants grown on contaminated soil. We have shown that the simultaneous planting of B. juncea with M. sativa and inoculation with PGPB were the most efficient variants of assisted phytoextraction reaching a recovery of 95% Zn, 90% Cd, and on average about 160% Pb compared with control B. juncea plants grown in monoculture.

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.