uptake by the plant. Due to this, physiological processes and various metabolic
activities get improved and adverse effects of physiological drought could minimize
in plants (Saxena et al. 2017).
1.2.5 Heavy Metal Stress
Extensive activities related to agriculture, industrialization, and urbanization are
adding enormous amount of heavy metals; for example, Arsenic (As), Cadmium
(Cd), Chromium, Lead (Pb), Mercury (Hg) in environment. Addition of excessive
amount of heavy metals damage and alter the soil texture, pH, thus affecting plant
growth and development. These toxic elements promote morphological, metabolic
abnormalities and thus disrupt cell homeostasis (Amari et al. 2017; Tiwari and Lata
2018).
Some of these metals are vital micronutrients, and are accountable for numerous
metabolic processes in a plant, but, if they exceed the threshold limit, these metals
can have detrimental effects on metabolic pathways, physiological processes, plant
growth and development, and finally senescence (Ghori et al. 2019). As a first line of
resistance exhibited, plants reduce the heavy metal uptake, through cellular and root
exudates that restrict entry of metals inside the cells (Shahid et al. 2015; Ghori et al.
2019). The second line of resistance involves adopting other mechanisms for
detoxification by transports, sequestration of these heavy metal ions, and chelates
in the plant’s vacuoles (Ghori et al. 2019). One of the most destructive effects caused
by heavy metals in plants is disruption of bio-membranes by lipid per-oxidation
(Demiral and Türkan 2005; Yadav 2010). Some of the harmful effects induced by
heavy metals are described below:
High concentration of Zinc results in stunted growth, chlorosis, senescence, and
changed root and shoot ratio (Fontes and Cox 1998; Yadav 2010). Another heavy
metal chromium is released from tanning industry. The excess availability of
chromium can bring chlorosis in young leaves, inhibit plant growth, nutrient imbalance, root injury, and wilting of tips (Scoccianti et al. 2006; Yadav 2010). Lead in
soil resulting from various sources like municipal sewage sludge, mining and
smelting activities, paints, gasoline and explosives, etc. It deteriorates plant growth,
morphology, and photosynthesis. Many enzymatic activities are inhibited when lead
concentration is very high, membrane permeability is lost, disturbs uptake of
mineral, and causes water imbalance (Sharma and Dubey 2005; Yadav 2010).
Recently, several studies revealed the physiological and molecular mechanisms of
arsenic toxicity, its accumulation, detoxification, and tolerance in various
concentrations in plants such as carrot, lettuce, rice, and spinach can cause several
physiological disorders (Kumar et al. 2015; Tiwari and Lata 2018).
1 Abiotic Stress in Plants: An Overview
9
activities get improved and adverse effects of physiological drought could minimize
in plants (Saxena et al. 2017).
1.2.5 Heavy Metal Stress
Extensive activities related to agriculture, industrialization, and urbanization are
adding enormous amount of heavy metals; for example, Arsenic (As), Cadmium
(Cd), Chromium, Lead (Pb), Mercury (Hg) in environment. Addition of excessive
amount of heavy metals damage and alter the soil texture, pH, thus affecting plant
growth and development. These toxic elements promote morphological, metabolic
abnormalities and thus disrupt cell homeostasis (Amari et al. 2017; Tiwari and Lata
2018).
Some of these metals are vital micronutrients, and are accountable for numerous
metabolic processes in a plant, but, if they exceed the threshold limit, these metals
can have detrimental effects on metabolic pathways, physiological processes, plant
growth and development, and finally senescence (Ghori et al. 2019). As a first line of
resistance exhibited, plants reduce the heavy metal uptake, through cellular and root
exudates that restrict entry of metals inside the cells (Shahid et al. 2015; Ghori et al.
2019). The second line of resistance involves adopting other mechanisms for
detoxification by transports, sequestration of these heavy metal ions, and chelates
in the plant’s vacuoles (Ghori et al. 2019). One of the most destructive effects caused
by heavy metals in plants is disruption of bio-membranes by lipid per-oxidation
(Demiral and Türkan 2005; Yadav 2010). Some of the harmful effects induced by
heavy metals are described below:
High concentration of Zinc results in stunted growth, chlorosis, senescence, and
changed root and shoot ratio (Fontes and Cox 1998; Yadav 2010). Another heavy
metal chromium is released from tanning industry. The excess availability of
chromium can bring chlorosis in young leaves, inhibit plant growth, nutrient imbalance, root injury, and wilting of tips (Scoccianti et al. 2006; Yadav 2010). Lead in
soil resulting from various sources like municipal sewage sludge, mining and
smelting activities, paints, gasoline and explosives, etc. It deteriorates plant growth,
morphology, and photosynthesis. Many enzymatic activities are inhibited when lead
concentration is very high, membrane permeability is lost, disturbs uptake of
mineral, and causes water imbalance (Sharma and Dubey 2005; Yadav 2010).
Recently, several studies revealed the physiological and molecular mechanisms of
arsenic toxicity, its accumulation, detoxification, and tolerance in various
concentrations in plants such as carrot, lettuce, rice, and spinach can cause several
physiological disorders (Kumar et al. 2015; Tiwari and Lata 2018).
1 Abiotic Stress in Plants: An Overview
9