SUMMARY
SUMMARY
Environmental stresses such as salinity, drought, heat, cold, flooding and
heavy metal toxicity are major threat to the agricultural productivity worldwide
(Gaafar et al., 2012). They are given special attention throughout the world due to
their toxic effects even at very low concentrations or at high concentrations (Stevovic,
et al., 2010). Today, several cases of human diseases, disorders, malfunction and
malformation of organs due to metal toxicity have been reported (Itumoh et al., 2013).
Once the heavy metals contaminate the ecosystem, they remain a potential threat for
many years. Thus, heavy metal contaminants causing ecological problems are of
global concern.
Cd is a heavy metal that normally occurs in low concentrations in soils and up
to 100-120 mg/kg dry weight was reported by Nwaichi et al. (2010). In plants, the
accumulation of Cd can cause numerous morphological and physiological changes.
Plants grown in soil containing high levels of Cd show visible symptoms of injury
reflected in terms of chlorosis, necrosis, leaf roll, growth inhibition, browning of root
tips and finally death (Sanita di Toppi and Gabbrielli, 1999; Wojcik and Tukiendorf,
2004; Benavides et al., 2005; Guo et al., 2008).
Generally, chromium is not considered as an essential element for plant
growth and development. Devries et al. (2002) reported that chromium is toxic to
higher plants at 100 μM kg-1. Moreover, hexavalent chromium compounds due to
their high solubility (James, 1996), easy permeability through biological membranes
and subsequent interaction with protein components and nucleic acids inside the cell
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SUMMARY
are comparatively more toxic than trivalent chromium. Chromium distribution in
crops has a stable character that is independent of the soil properties and content of
the element; usually the major concentration of the contaminant element is always
found in roots with minimum levels present in the vegetative and reproductive organs
(Golovatyj et al., 1999; Iyaka, 2009).
Keeping above details in view, this study was aimed to investigate:
1.
The effect of heavy metals on seed germination, growth and biomass
characteristics of pea and maize plants.
2.
The effect of heavy metals (cadmium and chromium) on physiological and
biochemical characteristics on pea and maize crop plants.
Pisum sativum L. is an annual crop, belongs to family Leguminoseae having
significant acceptance as green pea and also as pulses upon seed drying for the masses
in North India. Therefore, pea seeds were used to reveal cadmium contaminated
inhibition of water affecting seed germination, establishment and growth
characteristics in petriplates. Cadmium chloride (CdCl2) irrigation levels arranged
from 1 – 16ppm having cadmium contamination on short-term basis (till 15 days).
The long-term (upto 60 days) cadmium contaminated irrigation levels were applied in
earthern pots under field conditions. Accordingly, effect of cadmium toxicity was
elucidated in Pisum sativum to observe its consequences on plant growth,
physiological, biochemical and biomass characteristics of Pisum sativum. The plants
were grown as per protocol described in material and methods. The seeds were
subjected under short-term (till 15 days) to various cadmium concentrations to reveal
quick responses of pea seedlings in relation to their growth characteristics.
The fast kinetics for hydration/ imbibation found to be getting saturated within
6-8 hrs. It was found that germination percent decreased from 83 to 56%, and 39%
incase of 4 and 8 ppm cadmium contaminated water applied during seed germination
in petriplates. Almost 67% loss in seed germination reported while applying 16 ppm
concentration. The appearance of root, shoot and there biodynamics found to be
directelty influenced by the application of cadmium contaminated water irrigation.
The appearance of lateral roots also found to be affected depending upon the
treatment levels and duration along with loss in their voluminous growth. The root
and shoot biomass/ fresh mass found to be significantly correlated with the cadmium
treatment levels and duration both. Hence, higher the treatment levels and duration
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SUMMARY
both have affected much in impairing shoot and root fresh biomss. Consequently,it
has shown a strong correlation with the loss of photosynthetic pigments sugar and
proteins.
The bochemical molecules for ex. Sugar did down-regulated in contrast to the
stress inducible enzymes, i.e. CAT, POD, MDA and proline found to be up-regulated
to extend an ability of seedlings under stress. The amylase and metal tolerance (%) as
affected by higher cadmium accumulation gradually reduced. The loss in leaf number,
leaf and plant biomass, fruiting and seed yield etc. found to be impaired along with
higher levels and durations of the irrigation. Consequently gradual loss in harvest
index also found to be 49% (16 ppm).
Apart from all these, higher cadmium
contamination in irrigation water may also cause necrosis, chlorosis in pea.
In
conclusion Pisum sativum L. found to be differently susceptible as cadmium
contaminated water applied based either on short –long term irrigation duration under
laboratory and field conditions or both.
Maize (Zea mays L.) is world’s one of the three most popular cereal crops for
both livestock feed and human nutrition. With its high content of carbohydrates, fats,
proteins, some of the important vitamins and minerals, maize is the main food of the
lower-socio-economic populations and in some regions it represents more than 80%
of daily food consumption. Maize is widely cultivated throughout the world, and a
greater weight of maize is produced each year than any other grain.
Therefore, maize seeds were used to reveal chromium contaminated inhibition
of water affecting seed germination, establishment and growth characteristics in
petriplates. Chromium trioxide (CrO3) irrigation levels arranged from 1 – 16ppm
having chromium contamination on short-term basis (till 15 days). The long-term
(upto 90 days) chromium contaminated irrigation levels (upto 16 ppm) were applied
in earthen pots under field conditions. Accordingly, effect of chromium toxicity was
elucidated in Zea mays to observe its consequences on plant growth, physiological,
biochemical and biomass characteristics of Zea mays. The seeds were subjected under
short-term (till 15 days) to various chromium concentrations to reveal quick responses
of maize seedlings in relation to their growth characteristics.
The fast kinetics for hydration/ imbibation found to be getting saturated within
6-8 hrs. It was found that germination percent decreased from 87 to 57%, and 43%
incase of 4 and 8ppm chromium contaminated water applied during seed germination
in petriplates. Almost 57% loss in seed germination reported while applying 16 ppm
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SUMMARY
concentration. The morphological appearance such as root, shoot length,leaves per
plant and there biodynamics found to be down regulated parallel by the application of
chromium contaminated water irrigation. The appearance of roots also found to be
affected depending upon the treatment levels and duration along with loss in their
voluminous growth. The root and shoot biomass/ fresh mass found to be significantly
correlated with the chromium treatment levels and duration both. Hence, higher the
treatment levels and duration both have affected much in impairing shoot and root
fresh biomss. The morphological appearance based on retention/biogenesis of
photosynthetic pigments (chlorophylls and carotenoids) also found to be directly
down regulated with chromium levels and durations.
The biochemical molecules for example sugar did get down regulated in
contrast to the stress inducible enzymes, i.e. CAT, POD, MDA and proline found to
be up-regulated to extend an ability of seedlings under chromium stress. The
amylaseand metal tolerance (%) as affected by higher chromium accumulation
gradually reduced. The loss in flower, cobs and seed yield etc. were found to be
impaired along with higher levels and durations of the irrigation. Consequently
gradual loss in harvest index also found ca. 52% (16 ppm). Apart from all these,
higher chromium contamination in irrigation water may also cause necrosis and
chlorosis in maize. Thus it can be concluded that chromium irrigation had negative
impact over maize cultivar starting from seed germination to seedlings establishment
their growth and development processes. It may be due to adverse effects of
chromium over plant, based either on short-long term irrigation duration under
laboratory and field conditions or both. The biochemical molecules for example
protein did get down-regulated in contrast to the stress inducible enzymes for example
lipid peroxidase, proline, catalase and peroxidase as observed up-regulated under the
influence of cadmium and chromium treatments may be helping affected plants
intrinsically to support them for their viability.
The flower, pods and seed characteristics have also been reported and found
progressively reduced parallel with increasing levels of cadmium and chromium
irrigation. Consequently, biomass and harvest characteristics both found to be
impaired under the influence of cadmium and chromium as reported in the study.
Consequently, it is concluded that cadmium and chromium irrigation had negative
impact over pea and maize cultivars starting from seed germination to seedling
establishment their growth and development processes may be due to adverse effects
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SUMMARY
of cadmium and chromium over plants’ water holding capacity to retain ionic balance
coupled with osmotic stress or ion cytotoxicity due to excess heavy metals in plant
cell and its related functioning.
A long term exposure to heavy metals such as cadmium and chromium
produces oxidative stress in roots as already reported earlier. This s is being
confirmed through enzymatic and non enzymatic antioxidant defense system. Our
study also confirms that the cadmium and chromium disturbs the uptake and
distribution of essential nutrients such as nitrogen (N), iron (Fe) and zinc (Zn) due to
which certain essential metabolic processes are being disturbed in our experimental
plants i.e. pea and maize. It appears that sugar and chlorophyll concentrations were
adversely affected by the interference of cadmium and chromium in the Fe
metabolism in the plants. The disturbance in the protein synthesis in the studied plants
might have occurred due to the disturbance in the nitrogen metabolism of the plants,
caused by cadmium and chromium. The activities of antioxidative enzymes specially
Fe containing enzymes were also adversely affected by the toxic amount of two
studied heavy metals. As, these heavy metals might have interfered with Fe
metabolism in the plants. So far as the plant growth is concerned, it might have
adversely affected due to the interference of availability of two studied heavy metals.
Consequently our findings as reported have extended an overview about pea
and maize cultivation under the influence of differential levels of the cadmium and
chromium. It is found that pea and maize may be preferred to be cultivated in agroclimate areas either free from cadmium and chromium or may be less affected to
ensure crop improvement and crop productivity in relation to national economy
(socio-economy) and food safety security for the masses.
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