Toxic Metals/Metalloids Accumulation, Tolerance, and Homeostasis in Brassica Oilseed Species

Abstract

Brassica oilseed are economically important crops with greater heavy metals/metalloids tolerance ability and produce higher biomass (due to their genetically inherited traits). These species have different adaptive mechanisms to handle the toxic metal ions which attract plant scientists to fully understand the accumulation and tolerance mechanisms in order to minimize/remove the heavy metals/metalloids phytotoxicity. At physiological level, toxic heavy metal/metalloids impair the carbon assimilation (photosynthesis, etc.) and nitrate assimilation process that lead to yield reduction. A very common response of higher plants against heavy metals/metalloids toxicity is the overproduction of reactive oxygen species (ROS) and methylglyoxal (MG) which can cause proteins oxidation, enzymes inactivation/dysfunction, lipid peroxidation as MDA, DNA damages and interaction with cellular components. At the cellular level, toxic metal ions restrict the mechanisms of nutrients transport, disturbance in polynucleotide functions, disruption in cellular integrity which may be due to their interaction with biomolecules. These higher plants evolved antioxidant defense and glyoxalase enzymatic systems to scavenge the ROS-MG components. Also, the entry of toxic metal ions into the cell is restricted/sequestered (via efflux mechanisms) through the involvement of amino acids, glutathione, particularly heavy metals/metalloids binding ligands. GSH, being a central molecule of the defense system, directly/indirectly control (via metabolic enzymes, etc.) the reaction products of ROS-MG in plant cells, hence protection against heavy metals/metalloids induced oxidative damages. Brassica species synthesized chelating ligands (phytochelatins, metallothionein’s and organic acids etc.) ensured the detoxification, complexation, and compartmentation of toxic heavy metals/metalloids. These plants also possess transporter genes for their resistance against toxic metal ions and homeostasis. Thus, Brassica oilseed species utilize accumulation and transport mechanisms for improved tolerance. That’s, why Brassica species are ideal candidates to clean up the heavy metals/metalloids contaminated soils and their adaptive mechanisms against harsh environmental condition enhanced the suitability for phytoremediation technology. The adaptive potential of these plant species can assist to boost our understandings concerning the heavy metals/metalloids tolerance mechanisms and crops cultivation in contaminated soils.