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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.

Combating environmental stress related to the presence of toxic elements is one of the most important challenges in plant production. The majority of plant species suffer from developmental abnormalities caused by an exposure to toxic concentrations of metals and metalloids, mainly Al, As, Cd, Cu, Hg, Ni, Pb, and Zn. However, defense mechanisms are activated with diverse intensity and efficiency. Enhancement of defense potential can be achieved though exogenously applied treatments, resulting in a higher capability of surviving and developing under stress and become, at least temporarily, tolerant to stress factors. In this review, I present several already recognized as well as novel methods of the priming process called priming, resulting in the so-called “primed state” of the plant organism. Primed plants have a higher capability of surviving and developing under stress, and become, at least temporarily, tolerant to stress factors. In this review, several already recognized as well as novel methods of priming plants towards tolerance to metallic stress are discussed, with attention paid to similarities in priming mechanisms activated by the most versatile priming agents. This knowledge could contribute to the development of priming mixtures to counteract negative effects of multi-metallic and multi-abiotic stresses. Presentation of mechanisms is complemented with information on the genes regulated by priming towards metallic stress tolerance. Novel compounds and techniques that can be exploited in priming experiments are also summarized.

The increased frequency and intensity of drought periods is becoming a serious thread for agriculture, prompting the identification of crop species and cultivars with enhanced water stress tolerance. Drought responses were studied in four ornamental Sedum species under controlled greenhouse conditions, by withholding watering of the plants for four weeks. Determination of growth parameters (stem length, fresh weight) allowed establishing the relative degree of tolerance of the selected species as S. spurium > S. ochroleucum > S. sediforme > S. album. The levels of photosynthetic pigments (chlorophylls a and b and total carotenoids), oxidative stress [using malondialdehyde (MDA) as marker], non-enzymatic antioxidants (total phenolic componds and total flavonoids) and osmolytes (proline and total soluble sugars) were measured in leaves of control and stressed plants, to correlate drought tolerance with the activation of specific response mechanisms. The results obtained indicate that a higher tolerance to water deficit in Sedum is associated with: a) relatively lower stressinduced degradation of chlorophills and carotenoids, especially of the latter (which does not decrease in water-stressed plants of S. spurium, the most tolerant species); b) no increase in MDA levels; that is, lack of drought-induced oxidative stress and, consequently, no requirement to activate the synthesis and accumulation of antioxidant compounds; and c) higher proline levels in the non-stressed controls, which could be the basis of constitutive mechanisms of tolerance. However, proline concentrations are too low to have any significant osmotic effect, and its likely contribution to water deficit resistance in Sedumwould be due to its activity as 'osmoprotectant'. The identification of these biochemical markers of drought tolerance should help to develop rapid and efficient screening procedures to select Sedum taxa with enhanced tolerance when comparing different species within the genus, or different cultivars within a given species. Abbreviations Caro -total carotenoidsChl a -chlorophyll a Chl b -chlorophyll b MDA -Malondialdehyde (MDA),

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Two species of Pb-adapted shrubs, Alyssum montanum and Daphne jasminea, were evaluated in vitro for their tolerance to elevated concentrations of cadmium. Shoot cultures were treated with 0.5, 2.5, and 5.0 μM CdCl2 for 16 weeks and analyzed for their organogenic response, biomass accretion, pigment content, and macronutrient status. Cadmium accumulation and its root-to-shoot translocation were also determined. In both species, rooted microplantlets, suitable for acclimatization, were obtained in the presence of Cd applied as selection agent. In A. montanum, low and moderate dose of Cd stimulated multiplication, rooting, and biomass production. Growth tolerance index (GTI) in Cd-treated shoots ranged from 120 to 215%, while in the roots 51–202%. In turn, in Cd-treated D. jasminea proliferation and rooting were inhibited, and GTI for shoots decreased with increasing doses of Cd. However, roots exposed to Cd had higher biomass accretion. Both species accumulated Cd in developed organs, and its content increased with increasing CdCl2 dose. Interestingly, D. jasminea accumulated higher amounts of Cd in the roots than A. montanum and immobilized this metal in the root system. On the contrary, A. montanum translocated some part of accumulated Cd to the shoots, but with low efficiency. In the presence of Cd, A. montanum maintained macronutrient homeostasis and synthesized higher amounts of phytosynthetic pigments in the shoots. D. jasminea accumulated root biomass, immobilized Cd, and restricted its translocation at the expense of nutrient balance. Considering remediation potential, A. montanum could be exploited in phytoextraction, while D. jasminea in phytostabilization of polluted substrate.

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The importance of vanadium (V) in the functioning of land systems is extremely diverse, as this element may exert both positive and harmful effects on terrestrial organisms. It recently become considered an element of beneficial character with a range of applications for human welfare. The health-ameliorative properties of this transition element depend on its degree of oxidation and on optimal concentration in the target cells. It was found that a similar relationship applies to vascular plants. However, excessive amounts of vanadium in the environment contaminate the soil and negatively affect the majority of living organisms. A significantly elevated level of V results in the destabilization of plant physiological balance, slowing down the growth of biomass which significantly reduces yield. In turn, low doses of the appropriate vanadium ions can stimulate plant growth and development, exert cytoprotective effects, and effectively enhance the synthesis of some biologically active compounds. We present the scientific achievements of research teams dealing with such topics. The issues discussed concern the role of vanadium in the environment, particular organisms, and highlight its dualistic influence on plants. Achievements in the field of V bioremediation, with the use of appropriately selected microorganisms and plant species, are emphasized.