Sulfur-Oxidizing Bacteria Alleviate Salt and Cadmium Stress in Halophyte Tripolium pannonicum (Jacq.) Dobrocz.

The aim of this study was to investigate how introducing halophilic sulfur-oxidizing bacteria (SOB) Halothiobacillus halophilus to the growth substrate affects the physiological and biochemical responses of the halophyte Tripolium pannonicum (also known as sea aster or seashore aster) under salt and cadmium stress conditions. This study assessed the plant's response to these stressors and bacterial inoculation by analyzing various factors including the accumulation of elements such as sodium (Na), chloride (Cl), cadmium (Cd) and sulfur (S); growth parameters; levels of photosynthetic pigments, proline and phenolic compounds; the formation of malondialdehyde (MDA); and the plant's potential to scavenge 2,2-Diphenyl-1-picrylhydrazyl (DPPH). The results revealed that bacterial inoculation was effective in mitigating the deleterious effect of cadmium stress on some growth criteria. For instance, stem length was 2-hold higher, the growth tolerance index was 3-fold higher and there was a 20% increase in the content of photosynthetic pigments compared to non-inoculated plants. Furthermore, the SOB contributed to enhancing cadmium tolerance in Tripolium pannonicum by increasing the availability of sulfur in the plant's leaves, which led to the maintenance of an appropriate, about 2-fold-higher level of phenolic compounds (phenylpropanoids and flavonols), as well as chloride ions. The level of MDA decreased after bacterial application in all experimental variants except when both salt and cadmium stress were present. These findings provide novel insights into how halophytes respond to abiotic stress following inoculation of the growth medium with sulfur-oxidizing bacteria. The data suggest that inoculating the substrate with SOB has a beneficial effect on T. pannonicum's tolerance to cadmium stress.

Distinct co-tolerance responses to combined salinity and cadmium exposure in metallicolous and non-metallicolous ecotypes of Silene vulgaris.

This study compared co-tolerance to salinity and cadmium and investigated its mechanisms in a facultative metallophyte Silene vulgaris originating from distinct habitats. Shoots of calamine (Cal) and non-metallicolous (N-Cal) ecotypes grown in vitro were exposed to 10 and 100 mM NaCl, 5 µM CdCl2 and their combinations. Stress effects were evaluated based on growth, oxidative stress parameters, and DNA content and damage. Tolerance mechanisms were assessed by analyzing non-enzymatic antioxidants, osmolytes and ion accumulation. Irrespective of the ecotype, Cd stimulated shoot proliferation (micropropagation coefficients MC = 15.2 and 12.1 for Cal and N-Cal, respectively, growth tolerance index GTI = 148.1 and 156.7%). In Cal ecotype this was attributed to an increase in glutathione content and reorganization of cell membrane structures under Cd exposure, whereas in N-Cal to enhanced synthesis of other non-enzymatic antioxidants, mainly carotenoids and ascorbate. Low salinity stimulated growth of Cal ecotype due to optimizing Cl- content. High salinity inhibited growth, especially in Cal ecotype, where it enhanced DNA damage and disturbed ionic homeostasis. Species-specific reaction to combined salinity and Cd involved a mutual inhibition of Na+, Cl- and Cd2+ uptake. N-Cal ecotype responded to combined stresses by enhancing its antioxidant defense, presumably induced by Cd, whereas the metallicolous ecotype triggered osmotic adjustment. The study revealed that in S. vulgaris Cd application ameliorated metabolic responses to simultaneous salinity exposure. It also shed a light on distinct strategies of coping with combined abiotic stresses in two ecotypes of the species showing high plasticity in environmental conditions.

Insight into mechanisms of multiple stresses tolerance in a halophyte Aster tripolium subjected to salinity and heavy metal stress.

The study aimed at comparing metabolic reactions of a halophyte Aster tripolium to abiotic stresses. Profiling of endogenous phytohormones, soluble carbohydrates and stress-related amino acids was conducted in plants exposed to moderate and high salinity (150 and 300 mM NaCl), and heavy metal salts CdCl2 or PbCl2 (100 and 200 µM). High NaCl and Pb doses inhibited growth of A. tripolium (Stress Tolerance Index STI) of 37% and 32-35%, respectively. The plants tolerated moderate salinity and Cd (STI = 91% and STI = 83-96%, respectively). Toxic metals accumulated mainly in the roots but Cd translocation to the shoots was also observed. The stressors did not affect total concentrations of the main growth promoting phytohormones but we observed enhanced deactivation of auxins and gibberellins, and reduced accumulation of jasmonate precursor. ABA content increased under stress except for moderate salinity. A common reaction was also activation of osmotic adjustment, however it was disparately manifested under salinity and metallic stress. The distinct responses to salinity and metallic stresses involved changes in carbohydrate profile and altered interplay between salicylic acid content and the pool of active gibberellins. The content of active jasmonates diversified A. tripolium reactions to salt excess and each of the heavy metals. This parameter was linked to the accumulation of ethylene precursor. The results of the study can be used to decipher potential co-tolerance mechanism of this halophyte species to multiple environmental stresses.

A Circular Economy Approach to Restoring Soil Substrate Ameliorated by Sewage Sludge with Amendments.

This study examined the use of an artificial soil substrate in a mine waste reclamation area and its effect on plant metabolic functions. Research was conducted by determining the relationship between the plants' biochemical features and the properties of plant growth medium derived from post-flotation coal waste, sewage sludge, crushed stone and fly ash on the surface of the mine waste disposal area. Trees and shrubs were established on the material and allowed to grow for eight years. The study determined that the applied plants and the naturally occurring Taraxacum officinale were suitable for physio-biochemical assessment, identification of derelict areas and reclamation purposes. An evaluation of a soil substrate applied to post-mining areas indicated that it was beneficial for plant growth since it activated the metabolic functions of herbaceous plants, shrubs, and trees. The study showed that soil substrate can be targeted to improve plant stress tolerance to potentially toxic elements (PTEs). These data suggest the potential for growth and slower susceptible response to Cd, Cr, Cu, Fe, Mn, Ni, Pb and Zn. It is possible that the constructed soil-substitute substrate (biosolid material) would be an effective reclamation treatment in areas where natural soil materials are polluted by PTEs. This observation may reflect a more efficient use of soil substrate released from the cycling of organic biogene pools, in accordance with the circular economy approach. In further studies related to land reclamation using sewage sludge amendments, it would be necessary to extend the research to other stress factors, such as salinity or water deficiency.

Beet Molasses Enhance Salinity Tolerance in Thymus serpyllum-A Study under Greenhouse Condition.

The growing demand for Thymus serpyllum biomass to produce drugs, cosmetics and spices necessitates the search for innovative methods mitigating the negative effects of environmental stressors in order to improve its yield under unfavorable conditions. Due to the exposure of plants to salinity stress (SS), we investigated the effect of sugar beet molasses (SBM) on the growth and biochemical parameters related to plants' response to SS. Wild thyme plants were treated for 5 weeks to sodium chloride and 3% molasses solution using two modes of application (soil irrigation or foliar sprays). Plants irrigated by SBM showed slighter stem growth inhibition than control plants, high stress tolerance index and maintained a constant root water content under salt stress. Moreover plants treated with 100 mM NaCl and soil-applied SBM had lower lipid peroxidation level, showed lower POD activity, higher total soluble protein content and maintained a more even free amino acids level, compared to the control treatments. The concentration of potassium ions was higher in the case of plant roots irrigation with sugar beet molasses compared to control plants. In this experiment, most of the growth and biochemical parameters from foliar molasses-sprayed plants did not differ significantly from the control. We provided evidence that soil-applied SBM beneficially changed the plant's biochemical response to salt stress. On the basis of the obtained results, we conclude that this soil amendment contributes to the strengthening of plant protection against this harmful environmental factor.

Differential Tolerance to Lead and Cadmium of Micropropagated Gypsophila fastigiata Ecotype.

In vitro techniques may provide a suitable tool for effective propagation and conservation of plant species representing various ecological niches. The elaboration of such protocols is also prerequisite for selection of heavy-metal-tolerant plant material that could be afterwards used for restoration or remediation of polluted sites. In this study, culture protocol for Gypsophila fastigiata propagation was developed. The highest multiplication coefficient, which reached 6.5, and the best growth parameters were obtained on modified MS medium supplemented with 1.0 mg L-1 2iP and 0.2 mg L-1 IAA. The obtained cultures were treated with different concentrations of lead nitrate (0.1, 0.5, and 1.0 mM Pb(NO3)2) or cadmium chloride (0.5, 2.5, and 5.0 µM CdCl2). The growth parameters, photosynthetic pigments, and phenolic compound content were examined in order to evaluate whether tested metal salts can have an adverse impact on studied culture. It was ascertained that Pb ions induced growth disturbances and contributed to shoot wither. On the contrary, the proliferative shoot cultures were established on media containing Cd ions and the multiplication coefficients and shoot length increased on all media enriched with CdCl2. Chlorophylls and carotenoid contents were negatively affected by application of 5.0 µM of cadmium; nevertheless, in shoots treated with 2.5 µM CdCl2, increased accumulation of photosynthetic pigments occurred and their amount was similar to untreated culture. Adaptation to Cd was associated with stimulation of phenolic compound synthesis. Hence, we have reported on unambiguous positive result of in vitro selection procedure to obtain vigorous shoot culture tolerant to cadmium.

Recent strategies of increasing metal tolerance and phytoremediation potential using genetic transformation of plants.

Avoidance and reduction of soil contamination with heavy metals is one of the most serious global challenges. Nowadays, science offers us new opportunities of utilizing plants to extract toxic elements from the soil by means of phytoremediation. Plant abilities to uptake, translocate, and transform heavy metals, as well as to limit their toxicity, may be significantly enhanced via genetic engineering. This paper provides a comprehensive review of recent strategies aimed at the improvement of plant phytoremediation potential using plant transformation and employing current achievements in nuclear and cytoplasmic genome transformation. Strategies for obtaining plants suitable for effective soil clean-up and tolerant to excessive concentrations of heavy metals are critically assessed. Promising directions in genetic manipulations, such as gene silencing and cis- and intragenesis, are also discussed. Moreover, the ways of overcoming disadvantages of phytoremediation using genetic transformation approachare proposed. The knowledge gathered here could be useful for designing new research aimed at biotechnological improvement of phytoremediation efficiency.