Increase in Phytoextraction Potential by Genome Editing and Transformation: A Review

Soil metal contamination associated with productive activities is a global issue. Metals are not biodegradable and tend to accumulate in soils, posing potential risks to surrounding ecosystems and human health. Plant-based techniques (phytotechnologies) for the in situ remediation of metal-polluted soils have been developed, but these have some limitations. Phytotechnologies are a group of technologies that take advantage of the ability of certain plants to remediate soil, water, and air resources to rehabilitate ecosystem services in managed landscapes. Regarding soil metal pollution, the main objectives are in situ stabilization (phytostabilization) and the removal of contaminants (phytoextraction). Genetic engineering strategies such as gene editing, stacking genes, and transformation, among others, may improve the phytoextraction potential of plants by enhancing their ability to accumulate and tolerate metals and metalloids. This review discusses proven strategies to enhance phytoextraction efficiency and future perspectives on phytotechnologies.

Phytoextraction Potential of Arsenic And Cadmium And Response of Rhizosphere Microbial Community By Intercropping With Two Types of Hyperaccumulators

Intercropping with hyperaccumulators/accumulators is a promising alternative to enhance phytoextraction of heavy metal(loid)s in contaminated soil. In this research, a pot experiment was conducted to evaluate the influences of intercropping As hyperaccumulator Pteris vittata L. with Cd hyperaccumulator Sedum alfredii Hance or accumulator Hylotelephium spectabile (Boreau) H. Ohba on the plant growth, As and Cd phytoextraction, and rhizosphere bacterial microbiota. The results indicated that intercropping can promote the growth of plants. The total biomass of P. vittata, S. alfredii and H. spectabile in intercropping systems was significantly improved by 19.9% - 34.1%, 16.8% and 11.5%, respectively in comparison with corresponding plant monoculture. The As content in rhizoid and frond of P. vittata when intercropped with S. alfredii was increased by 28.3% and 19.0% (P < 0.05), respectively as compared with P. vittata monoculture, and this treatment acquired the maximum As and Cd accumulation with 2032 and 397 µg∙pot-1, respectively. Intercropping enhanced the soil bacterial community diversity. The genera of Lysobacter in S. alfredii rhizosphere soil and Massilia in P. vittata rhizosphere soil had higher abundance in the intercropping system of P. vittata and S. alfredii. And the significantly positive correlation relationships were found between Massilia, Lysobacter and plant As content, and Arthrobacter with plant Cd content, indicating that they may play important roles in As and Cd phytoextraction. The results suggested that intercropping P. vittata with S. alfredii could be a potential strategy for phytoextraction of As and Cd from co-contaminated soil.

Natural Fungal Endophytes From Noccaea caerulescens Mediate Neutral to Positive Effects on Plant Biomass, Mineral Nutrition and Zn Phytoextraction

Phytoextraction using hyperaccumulating plants is a method for the remediation of soils contaminated with trace elements (TEs). As a strategy for improvement, the concept of fungal-assisted phytoextraction has emerged in the last decade. However, the role played by fungal endophytes of hyperaccumulating plants in phytoextraction is poorly studied. Here, fungal endophytes isolated from calamine or non-metalliferous populations of the Cd/Zn hyperaccumulator Noccaea caerulescens were tested for their growth promotion abilities affecting the host plant. Plants were inoculated with seven different isolates and grown for 2 months in trace element (TE)-contaminated soil. The outcomes of the interactions between N. caerulescens and its native strains ranged from neutral to beneficial. Among the strains, Alternaria thlaspis and Metapochonia rubescens, respectively, isolated from the roots of a non-metallicolous and a calamine population of N. caerulescens, respectively, exhibited the most promising abilities to enhance the Zn phytoextraction potential of N. caerulescens related to a significant increase of the plant biomass. These strains significantly increased the root elemental composition, particularly in the case of K, P, and S, suggesting an improvement of the plant nutrition. Results obtained in this study provide new insights into the relevance of microbial-assisted phytoextraction approaches in the case of hyperaccumulating plants.

Phytoextraction and nutritional quality of forages cultivated in a constructed wetland system for wastewater treatment

This study aimed to evaluate the effects of different concentrations of sodium on the phytoextraction of nutrients and nutritional quality of forages (P. purpureum Schum and C. dactylon Pers) grown in wetland system constructed for wastewater generated in cattle slaughterhouses (WGCS) treatment. The experiment was conducted in a randomized complete block design with three replications. The treatments were tested using 2 x 5 factorial scheme, as follows: two species of grass (P. purpureum Schum and C. dactylon Pers) and five concentrations of sodium in WGCS: 70, 100, 150, 200 and 250 mg L-1. The phytoextraction potential of nutrients and the nutritional quality of forages grown in pots simulating a wetland system constructed for WGCS with sodium concentrations were assessed in terms of the contents of the nutrients nitrogen, phosphorus, potassium, calcium, magnesium and sodium in leaf tissues. The accumulations of these nutrients in the produced forages were also evaluated. Both species presented different behaviors regarding their nutrient phytoextraction potentials. The nutritional quality was changed in the forages due to the cultivation in constructed wetlands. Forage C. dactylon Pers presented higher phytoextraction potential of sodium and potassium and P. purpureum Schum presented a higher nutritional quality.

Toxic metal phytoextraction potential and health-risk parameters of some cultivated plants when grown in metal-contaminated river sediment of Danube, near an industrial town

Toxic metal phytoextraction potential of some higher plants, the white mustard (Sinapis alba L.), perennial rye grass (Lolium perenne L.) and also two cultivated plants, as green pea (Pisum sativum L. var. Rajnai törpe), radish (Raphanus sativus L. var. Szentesi óriás vaj), was studied in a field experiment, along the river Danube in close vicinity of an industrial town, Dunaújváros, Hungary. Soil/sediment and the various plant organs (leaves, stems and roots) were assessed for the contamination with some potentially toxic elements (PTE), such as the cadmium (Cd), nickel (Ni), copper (Cu), and zinc (Zn). It was found that Cd and Ni concentration was below, while the Cu and Zn elements were above the Hungarian permissible limits in each of the studied soil/sediment samples. Bioconcentration factor (BAF) was less than 1 in the shoot biomass of test plant samples and followed the order of Cu > Zn > Cd and Ni. Phytoremediation potential of selected test plants was found to be rather limited. The translocation factor (TF) was more than 1 for Cu and Zn elements, at each test plants. Cadmium was translocated into the leaves in case of the radish, only. Considering of the potential human daily intake of metals (DIM), it was less than 1 both for the adults and for the children. Health risk index (HRI) values of children, however, were higher than 1 for the Cd in case of radish, and for Zn and Cu in case of the pea. Results suggest that consumption of these plants grown in gardens of contaminated sediments can result in some risks for citizens in the industrial town of Dunaújváros. Further studies are required to identify appropriate plants with greater toxic metal phytoextraction potential.