3. Phyto remediation

Removing heavy metals from the environment is very difficult because their degradation, like other pollutants, is not possible either biologically or chemically

An innovative technique that is non-invasive, economical, and visually beautiful is phytoremediation. “phytoremediation,” uses plants to clean up the environment as they can extract, accumulate, and depollute the substrate (soil, air, and water) from the contaminants through physical, chemical, or biological processes. 

Metallothioneins, phytochelatins, metalloenzymes, metal-activated enzymes, and numerous metal storage, carrier, and channel proteins are among the many plant-based metal-binding proteins (MBPs) that play a major role in the phytoremediation of heavy metals.

 To increase their ability for phytoremediation, plants undergo genetic modification. Bacillus megaterium's expression of the mercuric ion-binding protein enhances Arabidopsis's ability to accumulate metals.

Phytoextraction

Plants uptake pollutants from soil, water, or sediments by their roots and transfer them to the aboveground biomass where they accumulate, such as in shoots or other harvestable parts of the plant. This is known as phytoextraction

Phytostabilization

Phytostabilization means establishing a plant covering the surface of polluted sites to limit the movement of contaminants within the vadose zone by root accumulation or immobilization inside the rhizosphere, therefore lessening off-site pollution. 

Phytovolatilization

Phytovolatilization refers to the use of plants to absorb heavy metal pollutants and transform them into volatile, less hazardous chemical species via transpiration. Some of the heavy metals, such as, Hg, and Se, may exist in the environment as gaseous species .

A small number of naturally occurring or genetically engineered plants, such as muskgrass (Chara canescens), Indian mustard (Brassica juncea), and Arabidopsis thaliana, have been shown to absorb heavy metals and transform them to gaseous forms within the plant before releasing them into the environment 

Metal-binding proteins in plants

Phytochelatins (PCs)

Plant PCs are cysteine-rich low-molecular-weight polypeptides that are synthesized enzymatically, and their formation is stimulated by the presence of heavy metals .PCs chelate heavy metals by using their thiol groups. The complexes of metals and PCs that are produced as a consequence are stored in vacuoles.

Metallothionein

Plants have developed some adaptations to tackle metal ion concentrations’ increase in soil. An excessive amount of essential metal ions also causes toxicity similar to the non-essential metal ions; the foresaid mechanism provides metal tolerance as well as plays a significant role in the detoxification of excessive metal ions. MT was first discovered in animals than in plants; plant MTs have been discovered only approximately 30 years ago.

Transporter proteins

The transporter proteins of the plants can uptake, translocate and, sequester the heavy metals to provide tolerance to the plants and eventually remediate the contaminated soil.