1.2.3 Responses of Aquatic Macrophytes to Heavy Metals
Some metals like Cu and Zn are required because of their role as micronutrients
needed for growth and upkeep by aquatic plants. But excessive amounts of these
metals can become toxic to plants. In response to heavy metal exposure, aquatic
plants, like terrestrial plants develop basic strategies to grow in metal contaminated
environment and they either grow as metal excluders or metal indicators or accumulators (Baker and Walker 1990). Wide range of aquatic plant species, such as
water hyacinths Eichhornia sp., (E. crassipes, E. azurea, E. diversifolia,
E. paniculata), Salvinia sp., (S. molesta, S auriculata, S. minima), water lettuce
(Pistia stratiotes), giant duckweed, duckweed (Lemna minor), Azolla sp., submerged
species such as Potamogeton sp. Myriophyllum sp. emergent species like Typha sp.
Scirpus sp. Limnocharis flava, Spartina sp., Cyperus sp. and Phragmites
sp. capabilities to reduce the concentration of heavy metals from polluted water
bodies (Soda et al. 2012; Rodriquez and Brisson 2015) because of this potential
aquatic plant species have gained attention to use in phytoremediation process.
Accumulation capacities of aquatic plants may vary from floating plants to emergent
plants.
Aquatic macrophytes respond to heavy metals towards biochemical parameters
after they accumulate metal ions from the environment which are very much specific
-specific. These responses depend on inherent characteristic of plants (Nayek et al.
2010). Loss in chlorophyll pigment (due to chloroplast destruction and replacement
of Mg
+2 of chloroplast by metal ion), Reduced sugar (corresponded with the
inhibition of photosynthesis or photosynthetic inhibition or respiration stimulation
for more energy requirement in metal stress condition. (John et al. 2008). In many
Aquatic macrophytes increase in total protein because of higher synthesis of metal
binding content due to the higher synthesis of metal binding proteins also known as
phytochelatins, high proline accumulation (due to increased biosynthesis of proline,
hyperactivity of antioxidant activities of catalase; CAT and peroxidase; POD (due to
over-production of reactive oxygen species (ROS) related to excess metal accumulation in leafy parts of aquatic macrophyte (Nayek et al. 2010). However, ascorbate
peroxidase (APX) may reduced or remained unchanged which may be due to
variation in the enzyme response that may vary with the plant species which produce
free radicles (Mazhoudi et al. 1997).
Aquatic plants cannot show avoidance towards unwanted changes in the surrounding environment. When concentration of heavy metals exceeds optimal level,
they trigger a sweeping physiological and biochemical amendment and also exert
adverse impacts on the plants both directly and indirectly. Heavy metals are known
to modify metabolic pathways of plants subjected to metal ions. This may prove
even detrimental to these plants. Heavy metals induce oxidative stress by producing
reactive oxygen species (ROS), Reduced or photosynthesis inhibition, respiration
and disintegration of cell organelles and finally the death of plants (Zhang et al.
2017; Sooksawat et al. 2013; Sneller et al. 2000).
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P. Parikh and K. Unadkat
Some metals like Cu and Zn are required because of their role as micronutrients
needed for growth and upkeep by aquatic plants. But excessive amounts of these
metals can become toxic to plants. In response to heavy metal exposure, aquatic
plants, like terrestrial plants develop basic strategies to grow in metal contaminated
environment and they either grow as metal excluders or metal indicators or accumulators (Baker and Walker 1990). Wide range of aquatic plant species, such as
water hyacinths Eichhornia sp., (E. crassipes, E. azurea, E. diversifolia,
E. paniculata), Salvinia sp., (S. molesta, S auriculata, S. minima), water lettuce
(Pistia stratiotes), giant duckweed, duckweed (Lemna minor), Azolla sp., submerged
species such as Potamogeton sp. Myriophyllum sp. emergent species like Typha sp.
Scirpus sp. Limnocharis flava, Spartina sp., Cyperus sp. and Phragmites
sp. capabilities to reduce the concentration of heavy metals from polluted water
bodies (Soda et al. 2012; Rodriquez and Brisson 2015) because of this potential
aquatic plant species have gained attention to use in phytoremediation process.
Accumulation capacities of aquatic plants may vary from floating plants to emergent
plants.
Aquatic macrophytes respond to heavy metals towards biochemical parameters
after they accumulate metal ions from the environment which are very much specific
-specific. These responses depend on inherent characteristic of plants (Nayek et al.
2010). Loss in chlorophyll pigment (due to chloroplast destruction and replacement
of Mg
+2 of chloroplast by metal ion), Reduced sugar (corresponded with the
inhibition of photosynthesis or photosynthetic inhibition or respiration stimulation
for more energy requirement in metal stress condition. (John et al. 2008). In many
Aquatic macrophytes increase in total protein because of higher synthesis of metal
binding content due to the higher synthesis of metal binding proteins also known as
phytochelatins, high proline accumulation (due to increased biosynthesis of proline,
hyperactivity of antioxidant activities of catalase; CAT and peroxidase; POD (due to
over-production of reactive oxygen species (ROS) related to excess metal accumulation in leafy parts of aquatic macrophyte (Nayek et al. 2010). However, ascorbate
peroxidase (APX) may reduced or remained unchanged which may be due to
variation in the enzyme response that may vary with the plant species which produce
free radicles (Mazhoudi et al. 1997).
Aquatic plants cannot show avoidance towards unwanted changes in the surrounding environment. When concentration of heavy metals exceeds optimal level,
they trigger a sweeping physiological and biochemical amendment and also exert
adverse impacts on the plants both directly and indirectly. Heavy metals are known
to modify metabolic pathways of plants subjected to metal ions. This may prove
even detrimental to these plants. Heavy metals induce oxidative stress by producing
reactive oxygen species (ROS), Reduced or photosynthesis inhibition, respiration
and disintegration of cell organelles and finally the death of plants (Zhang et al.
2017; Sooksawat et al. 2013; Sneller et al. 2000).
322
P. Parikh and K. Unadkat