350
P. Talukder
Plants and the metals in the soil have had a long and intimate evolutionary association
that has resulted in many complex interactions. Copper is an essential micronutrient
for plants. Plants maintain low copper concentration in the cells because at higher
concentrations, it behaves as a cytotoxic stress factor by generating reactive oxygen
species (ROS) and other free radicals (Cho and Seo 2005). Copper is an essential
micronutrient. Being a redox-active metal, excess accumulation of copper generates reactive oxygen species (ROS) (Stohs and Bagchi 1995). Copper toxicity is
accompanied with high rate of oxidative stress and lipid peroxidation (Díaz et al.
2001). Apart from producing ROS, heavy metals affect the plants either by binding
to the essential –SH groups of enzymes and hence inactivates them and make them
nonfunctional or they are also capable of replacing the essential functional elements
in prosthetic groups of the enzymes and interrupts their ability of catalysis. Among
the several mechanisms by which plants can cope with the ill-effects exerted by heavy
metals is the activation of the genes responsible for metallothionein and phytochelatin
production. Metallothioneins (MTs) are low molecular weight (7–8 kDa), Cysteinerich, metal-binding proteins (Blindauer and Leszczyszyn 2010); they can bind to a
variety of metals like zinc, copper, cadmium by forming mercaptide bonds. On the
other hand, Phytochelatins (PCs) are nonprotein, cysteine-rich peptides which are
biosynthesized enzymatically from the precursor Glutathione (GSH); heavy metals
like Cd, Pb, Zn, Cu can induce PC biosynthesis metallothionein combats oxidative
stress-induced heavy metals and phytochelatins, on the other hand, are involved in
nullifying oxidative stress induced by heavy metals only (Ghoshal et al. 2015).
Food habit in human has evolved over the course of human evolution and human
civilization. One of the main ingredients of our diet is vegetables. Brinjal [Solanum
melongena L. (Solanaceae)] is known to be the chief vegetable source of our diet. It is
the second most important vegetable in India after potato. In India, it is an important
part of our daily diet as it is a rich source of macro- and micronutrients (Shishira
et al. 2016). Being a fast-growing developing nation with such a huge population, it
is of utmost importance to increase the production of agricultural products including
vegetables such as brinjal. Due to rapid urbanization and industrialization, the amount
of agricultural land is decreasing day by day and farmers are now growing vegetables
in small hamlets nearer to the suburban areas. Unfortunately, the soil of those areas
is highly contaminated with heavy metals including copper due to various industrial
and anthropogenic activities. Hence, this present study is aimed to understand how
the plants can mitigate the effect of heavy metal toxicity by enhancing the expression
of the important genes of metallothionein and phytochelatin biosynthesis pathways
and hence by higher production of MT and PC which are capable of quenching the
heavy metals. This study would enable us to deduce a mechanism by which we can
reduce the amount of heavy metal-induced toxicity in vegetables which we consume
on a daily basis.
P. Talukder
Plants and the metals in the soil have had a long and intimate evolutionary association
that has resulted in many complex interactions. Copper is an essential micronutrient
for plants. Plants maintain low copper concentration in the cells because at higher
concentrations, it behaves as a cytotoxic stress factor by generating reactive oxygen
species (ROS) and other free radicals (Cho and Seo 2005). Copper is an essential
micronutrient. Being a redox-active metal, excess accumulation of copper generates reactive oxygen species (ROS) (Stohs and Bagchi 1995). Copper toxicity is
accompanied with high rate of oxidative stress and lipid peroxidation (Díaz et al.
2001). Apart from producing ROS, heavy metals affect the plants either by binding
to the essential –SH groups of enzymes and hence inactivates them and make them
nonfunctional or they are also capable of replacing the essential functional elements
in prosthetic groups of the enzymes and interrupts their ability of catalysis. Among
the several mechanisms by which plants can cope with the ill-effects exerted by heavy
metals is the activation of the genes responsible for metallothionein and phytochelatin
production. Metallothioneins (MTs) are low molecular weight (7–8 kDa), Cysteinerich, metal-binding proteins (Blindauer and Leszczyszyn 2010); they can bind to a
variety of metals like zinc, copper, cadmium by forming mercaptide bonds. On the
other hand, Phytochelatins (PCs) are nonprotein, cysteine-rich peptides which are
biosynthesized enzymatically from the precursor Glutathione (GSH); heavy metals
like Cd, Pb, Zn, Cu can induce PC biosynthesis metallothionein combats oxidative
stress-induced heavy metals and phytochelatins, on the other hand, are involved in
nullifying oxidative stress induced by heavy metals only (Ghoshal et al. 2015).
Food habit in human has evolved over the course of human evolution and human
civilization. One of the main ingredients of our diet is vegetables. Brinjal [Solanum
melongena L. (Solanaceae)] is known to be the chief vegetable source of our diet. It is
the second most important vegetable in India after potato. In India, it is an important
part of our daily diet as it is a rich source of macro- and micronutrients (Shishira
et al. 2016). Being a fast-growing developing nation with such a huge population, it
is of utmost importance to increase the production of agricultural products including
vegetables such as brinjal. Due to rapid urbanization and industrialization, the amount
of agricultural land is decreasing day by day and farmers are now growing vegetables
in small hamlets nearer to the suburban areas. Unfortunately, the soil of those areas
is highly contaminated with heavy metals including copper due to various industrial
and anthropogenic activities. Hence, this present study is aimed to understand how
the plants can mitigate the effect of heavy metal toxicity by enhancing the expression
of the important genes of metallothionein and phytochelatin biosynthesis pathways
and hence by higher production of MT and PC which are capable of quenching the
heavy metals. This study would enable us to deduce a mechanism by which we can
reduce the amount of heavy metal-induced toxicity in vegetables which we consume
on a daily basis.