Journal of Environmental Biology ?January, 2007?
Biochemical parameters of plants as indicators of air pollution
A. K. Tripathi and Mukesh Gautam*
Ecology and Environment Division, Forest Research Institute, Dehradun-248 006, India
(Received: August 5, 2005 ; Revised received: December 22, 2005; Accepted: January 14, 2006)
Abstract: In the present study, species like Mangifera indica, Linn., Cassia fistula, Linn., and Eucalyptus hybrid were exposed to different air pollution
load for short duration (active biomonitoring). Variation in biochemical parameters like chlorophyll, protein, soluble sugar, free amino acid, ascorbic acid,
nitrate reductase, superoxide dismutase and peroxidase in the leaves were found to be pollution load dependent. These variations can be used as
indicators of air pollution for early diagnosis of stress or as a marker for physiological damage to trees prior to the onset of visible injury symptoms. Just
by analyzing these biochemical indicators air quality can also be assessed.
Key words: Bioindicators, Superoxide dismutase, Nitrate reductase, Peroxidase
Air pollution is one of the severe problems world facing
today. It deteriorates ecological condition and can be defined as
the fluctuation in any atmospheric constituent from the value that
would have existed without human activity. Various efforts have
been done for environmental restoration in India but still it seems
to be a formidable task. Dehradun valley is no exception. Its
environment has undergone irreparable damage due to the
population growth and its subsequent requirements in terms of
housing and traffic density. Continuously increasing road traffic
is a primary culprit. The changed ambient environment due to
the air pollutants in urban area of Dehradun has exerted a
profound influence on the morphological, biochemical and
physiological status of plants, and therefore its responses. To
assess the seriousness of the air pollution threat and to take
effective actions, the components of an urban air quality
management should also include a biological monitoring to
complement the instrumental air quality monitoring. It will provide
the necessary feedback information about receptor conditions in
the face of regional pollutant emissions. National Forest Policy,
1988 clearly directs that forests be managed first as an ecological
necessity, second as a source of goods for local populations and
only third as a wood for industries. Since plants and trees are
the ecological necessity and air pollutants cause large scale
damage to these, therefore policy makers must consider the
sensitivity of the plant receptors before prescribing the
standards or framing the emission control policies in Indian
air quality management system. Until now, data on pollutant
effects on biological parameters at any level have almost never
been used to set allowable levels of emissions in air quality
monitoring programmes in Dehradun valley. Research needs
to be expanded to encompass a greater variety of plant
responses to interactive stresses caused by air pollutants in
more realistic field conditions.
*Corresponding author: E-mail: firstname.lastname@example.org, Tel.: 0135-2752674(O), 2750449 (R), Fax: 0135-2756865
The main focus of this work is to provide an assessment
of the use of biochemical parameters of plants as indicators of
air pollution so that these biochemical indicators can be used for
air quality monitoring in urban areas of Dehradun, the capital of
Uttaranchal. The proposed study will provide a technical support
to the air quality management in the city of Dehradun. The data
generated will help us to find out the exact position i.e. success
or failure of the regulatory measures which have been taken and
also the corrective measures which are required to take up to
bring the system to its normal or pristine stage.
Materials and Methods
Method selection: Active and passive biomonitoring are the two
methods which can be applied to evaluate the applicability of the
biochemical parameters of plants as indicators of air pollution.
Here active biomonitoring method was opted which consists of
exposing potted test plants to the polluted areas for short duration
i.e. for three months (Klumpp, 2003).
Species selection: Species were selected on the basis of
air pollution tolerance index (APTI). Species having APTI
less than 10 are termed as sensitive species and can be
used for the biomonitoring of air pollutants (Agrawal et al.,
1991). APTI of five forest tree species (Mangifera indica,
Linn., Cassia fistula, Linn., Eucalyptus hybrid, Grevillea
robusta, A. Cunn. and Dalbergia sissoo, Roxb.) was
calculated by using the method given by Singh and Rao
(1983). Mangifera indica, Linn (APTI 8.10), Cassia fistula,
Linn. (APTI 7.56) and Eucalyptus hybrid (APTI 8.69) were
selected to use their biochemical parameters as bio
indicators of air pollution and were grown in polybags for
one year. Four plants of each species were exposed to air
pollution for three months (October to December, 2004) at
selected bioindicator stations.
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Journal of Environmental Biology ?January, 2007?
A. K. Tripathi and Mukesh Gautam
Site selection/bioindicator station selection: Total three
bioindicator stations including urban and suburban sites, close
to streets with heavy and light pollution load were identified and
Forest Research Institute (FRI) was treated as control site. Details
of sites are :
Bioindicator station 1 - Darshan lal chowk (Near clock tower)
Bioindicator station 2 - Mohkampur (Haridwar road)
Bioindicator station 3 - Mohebewala (Dehradun-Delhi road)
Control site - FRI
Air quality analysis (SO2 , NOx and SPM): During the exposure
period, ambient air quality in terms of common air pollutants i.e.
SO2, NOx and SPM was analysed at all the bioindicator stations.
Sampling was done 24 hr and twice in a week during the exposure
period. Average of 24 hr such sampling was taken for final
calculation. For the collection of samples for SPM from ambient
air, GF/A filter paper was used in high volume sampler (HVS) at
the flow rate of 1.0 to 1.5 m3/min. SPM was computed as per
standard method. Filter paper was weighed before and after
sampling. West and Gaeke method (1956) and modified Jacob
and Hochheiser method (1958) were used for analysis of SO2
and NOx respectively.
Air pollution index (API): The average of the sum of the ratios
of three major pollutant concentrations to their respective air
quality standards were obtained. The average was then multiplied
by 100 to get the index (Rao and Rao, 1989).
where SSPM, SSO2 and SNOx represent the ambient air
quality standards for SPM, SO2 and NOx.
Air pollution index of bioindicator stations were
developed on the basis of ambient air quality analyzed at specified
bioindicator stations through instrumental monitoring of SPM, SO2
and NOX and correlated with the variation in biochemical
indicators. On the basis of air pollution index, bioindicator station
1 was categorized as severe air pollution site (air pollution index
117.66), station 2 as heavy air pollution site (air pollution index
82.33) and station 3 as moderate air pollution site (air pollution
index 70.00) (Table 1 and 2).
Biochemical parameters: After three months of the exposure,
plants were brought back to the institute and leaf samples were
analysed for different biochemical parameters. Total chlorophyll
was analysed following the method of Arnon (1949), ascorbic
acid by Sadasivam and Balasubraminan (1987), protein by Lowry
et al. (1951), total soluble sugars by phenol sulphuric acid method
of Dubois et al. (1951), free amino acid by Moore and Stein (1948),
Table-1: Ambient air quality and air pollution index for different
Pollutants (µ µ µ µg/m3)
Air pollution index
23.90Station No. 1 395 117.66
(Severe air pollution)
(Heavy air pollution)
(Moderate air pollution)
Station No. 2275 13.35 17.41
Station No. 3 215 15.6419.13
(Ambient air quality standards taken for calculation of air pollution
i n d e x 1 4 0 µg/m3 for SPM, 60 µg/m3 for SO2 and 60 µg/m3 for NOx )
Table-2 : Rating scale for indices (ref)
Index value Remarks
Light air pollution
Moderate air pollution
Heavy air pollution
Severe air pollution
Table-3 : Biochemical Indicators of different species at different bioindicator stations
N R (µ µ µ µmole
g-1 FW hr-1)
Px (changes in
C. fistula Control
Data represent mean of four replicates. Results are significant at 0.1% (p<0.001)
API = 1/3 [+
] X 100
Journal of Environmental Biology ?January, 2007?
Biochemical indicators of air pollution
superoxide dismutase by Sangeetha et al. (1990), peroxidase
by Malick and Singh (1980) and nitrate reductase by Jaworski’s
(1971) method. Results were statistically analysed and interpreted
for drawing conclusions.
Results and Discussion
After three months of exposure, leaf samples of the
plant species were analysed for chlorophyll, protein, soluble sugar,
free amino acids and some of the enzymatic parameters like
nitrate reductase, superoxide dismutase and peroxidase activity.
All the biochemical indicators exhibited significant
variation (p<0.001) from species to species and station to station
Mangifera indica, Linn.: At station 1, Mangifera indica, Linn.
exhibited 3.6% reduction in chlorophyll content while increase of
12.8% and 7.6% was observed at stations 2 and 3 respectively.
Significant reduction (2.7%) in protein content was observed at
station 1, followed by a loss of 0.98% at station 2, whereas at
station 3, gain of 3.5% was evident. All the stations showed
significant reduction in soluble sugar (p<0.001). Maximum
reduction (17.1%) in soluble sugar was exhibited at station 1
followed by 4.9% and 1.1% at stations 2 and 3 respectively. Free
amino acid exhibited an increasing trend at all the stations.
Maximum gain of 43.9% was evident at station 1 followed by
13.4% and 12.4% at stations 3 and 4. Ascorbic acid also showed
increase over control at all the stations. Maximum enhancement
of 84.6% was exhibited at station 1, followed by 51.9% each at
stations 2 and 3. Nitrate reductase activity was also found to be
increasing at all the stations. Maximum increase (39.6%) was
observed at station 1, followed by station 3 (13.1%) and station
2 (9.1%). Superoxide dismutase activity varied positively at all
the stations. Maximum stimulation of 20.9% was revealed at
station 1 followed by 8.7% at station 2 and 3.7% at station 3.
Positive trend was also observed in case of peroxidase activity
at all the stations. Station 1 exhibited maximum increase (56%)
followed by station 3 (55%) and station 2 (42.9%) (Table 3 and
Cassia fistula, Linn.: Biochemical indicators of Cassia fistula, Linn.
at all the bioindicator stations varied significantly (p<0.001) (Table
3 and Fig. 2). Maximum reduction (66.4%) in chlorophyll content
was observed at station 1 while at station 2 and 3, loss of 35.1%
and 18% was observed. At all the stations, protein content showed
significant reduction. Maximum loss of 33.8% was exhibited at
station 1 followed by 27.3% and 23.6% at stations 2 and 3
respectively. Soluble sugar showed maximum loss of (43.7%) at
station 1 followed by 25.8% at station 2 and 18.3% at station 3.
Like Mangifera indica, Linn., Cassia fistula, Linn. also showed
increasing trend of free amino acids at all the stations as
compared to control values. Station 1 exhibited maximum
enhancement (41.6%) in free amino acids followed by station 2
(18.2%) and station 3 (6.8%). Ascorbic acid was also found to be
increasing at all the stations as compared to control. Maximum
increase of 49.8% was evident at station 1 followed by 26.3% at
station 3 and 0.5% at station 2. Stimulation in nitrate reductase
activity was observed at all the stations as compared to control.
Maximum stimulation (104.8%) was observed at station 1 followed
by 84.9% at station 3 and 52.7% at station 2. Stimulating trend
was also observed in case of superoxide dismutase activity at all
the stations. At station 1, 9.2% stimulation was observed followed
by 8.15% at station 3 and 6.1% at station 2. Like other enzymatic
activities, peroxidase activity was also found be more at all the
ChlorophyllProtein Sugar Amino acidAscorbic acid NR activity SOD activityPer. Activity
Fig. 1: Variation in biochemical indicators of Mangifera indica at different bioindicator stations
Journal of Environmental Biology ?January, 2007?
stations, as compared to control. Maximum stimulation of 67.6%
was exhibited by the species exposed at station 2, followed by
58.8% at station 1 and 17.6% at station 3 (Table 3 and Fig. 2).
Eucalyptus hybrid: Chlorophyll content at station 1 showed 22%
reduction, followed by 14% reduction at station 2 and 3.7% at
station 3, as compared to control (p<0.001). Increase in protein
content was exhibited at all the stations. Maximum increase
(11.7%) was observed at station 3 followed by station 1 (4.8%)
and station 2 (0.7%) at all the stations. Soluble sugar was found
to be significantly reduced (p<0.001). Maximum reduction (11.6%)
was revealed at station 1 followed by station 3 (7.1%) and station
2 (1.15%). Free amino acids were found to be more at all the
stations as compared to control. Maximum enhancement (26%)
in free amino acid was exhibited at station 1 followed by 17.25%
at station 2 and 12.3% at station 3. Ascorbic acid content was
significantly increased at all the stations and again maximum
gain (32.9%) was observed at station 1 followed by station 2
(20.48%) and station 3 (4.2%). Enzymatic activities like nitrate
reductase, super oxide dismutase and peroxidase were found to
be higher than respective control values. Maximum increase
(61.6%) in nitrate reductase activity was evident at station 1
followed by station 2 (51.5%) and station 3 (43.0%). Super oxide
dismutase activity increased 11.0% at station 1, 8.3% at station
2 and 5.1% at station 3 as compared to control. Peroxidase activity
exhibited maximum stimulation (56.6%) at station 1, followed by
37.7% each at station 2 and 3 (Table 3 and Fig. 3).
Although all the species showed significant variation
in all the biochemical indicators, the extent up to which plant
species were affected varied from species to species and station
to station. Almost all the species showed maximum variation in
biochemical indicators at station 1, which is found to be severe
air pollution site. A considerable loss in total chlorophyll, in the
leaves of plants exposed at station 1 (severe air pollution site)
supports the argument that the chloroplast is the primary site of
attack by air pollutants such as SPM, SO2 and NOX. Air pollutants
make their entrance into the tissues through the stomata and
ChlorophyllProteinSugar Amino acid Ascorbic acidNR activity SOD activityPer. Activity
Fig. 2: Variation in biochemical indicators of Cassia fistula at different bioindicator stations
Chlorophyll ProteinSugar Amino acidAscorbic acid NR activity SOD activityPer. Activity
Fig. 3: Variation in biochemical indicators of Eucalyptus hybrid at different bioindicator stations
A. K. Tripathi and Mukesh Gautam 130
Journal of Environmental Biology ?January, 2007?
cause partial denaturation of the chloroplast and decreases
pigment contents in the cells of polluted leaves. Rao and Leblanc
(1966) mentioned that high amount of gaseous SO2 causes
destruction of chlorophyll and that might be due to the
replacement of Mg++ by two hydrogen atoms and degradation of
chlorophyll molecules to phaeophytin. In Cassia fistula, Linn. and
Eucalyptus hybrid, maximum depletion in chlorophyll content at
station 1 may be due to the maximum pollution load at this site
whereas station 2 and 3 showed less depletion due to lower
Reduction in protein content in Cassia fistula, Linn. at
all the stations while station 1 in case of Mangifera indica, Linn.
might be due to the enhanced rate of protein denaturation which is
also supported by the findings of Prasad and Inamdar (1990).
Constantinidou and Kozlowski (1979) found enhanced protein
denaturation and breakdown of existing protein to amino acid as
the main causes of reduction in protein content.
Soluble sugar is an important constituent and source of
energy for all living organisms. Plants manufacture this organic
substance during photosynthesis and breakdown during respiration.
Our study revealed significant loss (p<0.001) of soluble sugar in
all the species at all the stations. All the species showed maximum
loss at severe air pollution site i.e. at station 1, followed by heavy
air pollution site (station 2) and moderate air pollution site (station
3). The concentration of soluble sugars is indicative of the
physiological activity of a plant and it determines the sensitivity of
plants to air pollution. Reduction in soluble sugar content in polluted
stations can be attributed to increased respiration and decreased
CO2 fixation because of chlorophyll deterioration. Davison and
Barnes (1986) mentioned that pollutants like SO2, NO2 and H2S
under hardening conditions can cause more depletion of soluble
sugars in the leaves of plants grown in polluted area. The reaction
of sulfite with aldehydes and ketones of carbohydrates can also
cause reduction in carbohydrate content.
All the species showed increased free amino acids at all
the stations but it varied with the air pollution load. Severe air
pollution site i.e. station 1 exhibited maximum increase of free amino
acids as compared to control and other stations. More free amino
acids at severe air pollution site may be due to more nitrate
reductase activity or may also be due to more protein denaturation
at this station.
Present investigation revealed a great deal of variation
in the levels of ascorbic acid in all the species at all the stations.
Pollution load dependent increase in ascorbic acid content of all
the species may be due to the more rate of production of reactive
oxygen species (ROS) such as SO3
photooxidation of SO3
SO2 absorbed. The free radical production under SO2 exposure
would increase the free radical scavengers, such as ascorbic acid,
super oxide dismutase, peroxidase etc. (Pierre and Queirz, 1981)
based on dosage and physiological status of plant. Increased level
-, OH-, O2
- etc. during
- to SO4
- where sulfites are generated from
of ascorbic acid may be due to the defense mechanism of the
Nitrate reductase is a metalloflavoprotein inducible
enzyme which catalyses the reduction of nitrate to nitrite. It
acts as a rate limiting step and regulatory enzyme in the
pathway NO3 NO2 NH4 amino acids, and its
activity often controls the overall assimilation rate of nitrate. There
are two distinct pools for nitrate in plant tissues i.e. storage and
metabolic pools, only nitrate of the metabolic pool functions as a
substrate for NR and contributes to organic nitrogen. In the present
investigation air pollution load dependent increase in NR activity
may be due to the more availability of nitrate in the metabolic pool
of the plants at more polluted site. The source of the nitrate may
be the NOx pollutants in the atmosphere. Zeevaart (1974) found
induction of nitrate reductase activity in plants by atmospheric NO2.
Superoxide radicals (O2
potential secondary oxy radicals, thus removal of superoxide
radicals is a detoxification process or indirect protective action.
SOD, catalase and peroxidase serve as interlinked primary
protection mechanism. SOD along with catalase and peroxidase
that acts on the end product (H2O2) of SOD activity can interact to
regulate injurious oxy radicals and peroxyl concentrations in cells
and organelles and determine equilibrium rates (Bennett et. al.,
1984). SOD increases and can protect cells against free radicals
produced by air pollutants by catalyzing following reaction to form
H2O2 (Scandalios, 1993).
-) are less toxic than other
- + 2H+ H2O2 + O2
H2O2 is the end product and is broken down by
peroxidase into H2O and O2. In the present study SOD and
peroxidase activities in all the species were found to be maximum
at severe air pollution station than other stations. This may be due
to the more interlinked primary protection mechanism offered by
SOD and peroxidase in plants to protect themselves at severe air
pollution station as compared to the less polluted sites. Increased
resistance of plants may be correlated with increased SOD activity
(Tanaka et al., 1982).
In view of the data obtained in present investigation it
seems reasonable to conclude that SOD play significant role in
protecting living cells against the toxicity of active O2
Varshney and Varshney (1985) reported increase in peroxides
activity in plant cells under a variety of stresses, such as mechanical
injury and attack by pathogen or an influence of environmental
pollution. The increase in peroxides activity varies with the plant
species and the concentration of pollutants. Khan and Malhotra
(1982) reported that leaves of the resistant plants might have high
Data on ambient pollutant concentrations do not allow
direct conclusions to be drawn on potential impacts on plants and
the environment. Evidence of effects can only be provided by using
Biochemical indicators of air pollution131
Journal of Environmental Biology ?January, 2007? Download full-text
plants itself as monitors. These types of plant bioindicators integrate
the effects of all environmental factors including interactions with
other pollutants or climatic conditions. This permits the risk of
complex pollutant mixtures and chronic effects occurring even below
threshold values to be assessed. Therefore use of plants, as
bioindicators is inexpensive and easy technique. Merely by
analyzing the present parameters, an early diagnosis of the extent
of pollution can be done in the absence of visible injury.
Authors thank Dr. (Mrs.) P. Soni, Head, Ecology and
Environment Division for her valuable suggestions and Forest
Research Institute, Dehradun for financial support.
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