Apart from this, restarted growth (specially roots), chlorosis and necrosis of leaf
like symptoms observed in plants exposed to heavy metals represent some phytotoxic responses followed by abscission as well as senescence that ultimately results
into less nutrient uptake and which in turn interfere with the acquired biomass. For
instance, Cd and Cu cause many abnormal structures related to morphological (such
as breaking of roots, necrosis and colony disintegration, root break-up) and physiological (such as photosynthesis, pigment synthesis and enzyme activity) parameters
of aquatic plants (Khellaf and Zerdaoui 2010; Xing et al. 2010). However, these
responses depend on various factors like metal concentration, time of exposure,
presence of more than one metal ion in the solution etc. For e.g., Eichhornia
crassipes at 6 mg/l As concentration caused death on exposure to the metal at
8 days period but the plants are able to survive in Zn metal exposure at the same
concentration i.e. 6 mg/l (Hasan et al. 2007). An Emergent Aquatic plant Typha
capensis in the presence of As, Hg, Cd and Pb (multimetal solution) showed
inhibition in the absorption (Wiafe et al. 2019). Nirogen metabolism which plays a
crucial role in regulating growth and development of plant right from metabolism to
distribution of resources among various plant parts is severely affected once heavy
metal enter accumulated by plant body.
Like terrestrial plants, Aquatic Plants respond to detrimental effects of heavy
metals through several mechanism. At first, they sense this heavy metal stress
stimuli, alert transduction and transmission of signals into the cell, activating
congruous measures to escape the negative effects heavy metal stress by
harmonising molecular, physiological and biochemical status of the cell.
1.2.4 Adaptive Strategies of Aquatic Macrophytes
Plants possess a sophisticated and interrelated network of defence strategies due to
which they can either avoid or tolerate intoxication to heavy metals. Physical fence
are the first line of developing shield against metals in plants. These include presence
of thick cuticle and trichomes (which are biologically active tissues), cell walls and
also symbiosis with mycorrhiza (in terrestrial plants.) (Hall 2002; Wong et al. 2004;
Harada et al. 2010). Structures like trichomes can store heavy metal ions; thus, helps
in detoxification process and they also secrete secondary metabolites which protect
the plants against hazardous effects of metals.
On the other hand, if heavy metal ions enter into cells and tissues of plants; they
commence several cellular defence mechanisms which weaken and nullify harmful
effects of metal ions. The primary way to endure or neutralize toxicity of metal ions,
the plants synthesize various biomolecules such as low-molecular weight proteins
like phytochelatins (PCs) and metallothionein (MT) which function as metal chelators. These chelators are the best designated sulphur-containing metal-binding
ligands. They are known to contribute to metal homeostasis, the purpose being
again detoxification. This they accomplished by buffering cytosolic metal concentrations (Verkleij and Sachat 1990). Heavy metals are known to bind to the thiol (–
SH) that have low molecular weight showing a very high affinity for metals specially
15 Potential of Free Floating Macrophytes for Bioremediation of Heavy Metals. . .
323
like symptoms observed in plants exposed to heavy metals represent some phytotoxic responses followed by abscission as well as senescence that ultimately results
into less nutrient uptake and which in turn interfere with the acquired biomass. For
instance, Cd and Cu cause many abnormal structures related to morphological (such
as breaking of roots, necrosis and colony disintegration, root break-up) and physiological (such as photosynthesis, pigment synthesis and enzyme activity) parameters
of aquatic plants (Khellaf and Zerdaoui 2010; Xing et al. 2010). However, these
responses depend on various factors like metal concentration, time of exposure,
presence of more than one metal ion in the solution etc. For e.g., Eichhornia
crassipes at 6 mg/l As concentration caused death on exposure to the metal at
8 days period but the plants are able to survive in Zn metal exposure at the same
concentration i.e. 6 mg/l (Hasan et al. 2007). An Emergent Aquatic plant Typha
capensis in the presence of As, Hg, Cd and Pb (multimetal solution) showed
inhibition in the absorption (Wiafe et al. 2019). Nirogen metabolism which plays a
crucial role in regulating growth and development of plant right from metabolism to
distribution of resources among various plant parts is severely affected once heavy
metal enter accumulated by plant body.
Like terrestrial plants, Aquatic Plants respond to detrimental effects of heavy
metals through several mechanism. At first, they sense this heavy metal stress
stimuli, alert transduction and transmission of signals into the cell, activating
congruous measures to escape the negative effects heavy metal stress by
harmonising molecular, physiological and biochemical status of the cell.
1.2.4 Adaptive Strategies of Aquatic Macrophytes
Plants possess a sophisticated and interrelated network of defence strategies due to
which they can either avoid or tolerate intoxication to heavy metals. Physical fence
are the first line of developing shield against metals in plants. These include presence
of thick cuticle and trichomes (which are biologically active tissues), cell walls and
also symbiosis with mycorrhiza (in terrestrial plants.) (Hall 2002; Wong et al. 2004;
Harada et al. 2010). Structures like trichomes can store heavy metal ions; thus, helps
in detoxification process and they also secrete secondary metabolites which protect
the plants against hazardous effects of metals.
On the other hand, if heavy metal ions enter into cells and tissues of plants; they
commence several cellular defence mechanisms which weaken and nullify harmful
effects of metal ions. The primary way to endure or neutralize toxicity of metal ions,
the plants synthesize various biomolecules such as low-molecular weight proteins
like phytochelatins (PCs) and metallothionein (MT) which function as metal chelators. These chelators are the best designated sulphur-containing metal-binding
ligands. They are known to contribute to metal homeostasis, the purpose being
again detoxification. This they accomplished by buffering cytosolic metal concentrations (Verkleij and Sachat 1990). Heavy metals are known to bind to the thiol (–
SH) that have low molecular weight showing a very high affinity for metals specially
15 Potential of Free Floating Macrophytes for Bioremediation of Heavy Metals. . .
323