Effect of Particulate Pollution on various Tissue Systems of Tropical Plants

By Dr. Dipu Sukumaran
February 2012

The author is a Research Associate with the Central Pollution Control Board (CPCB), Zonal Office, Kolkata, India

Abstract
The problem of impact of air pollutants on vegetation is quite complex. Our knowledge on the impact of air pollutants on different plant species comes largely from the morphological and physiological investigations. The effects of pollutants on different anatomical traits have conceived relatively little attention. The observations recorded in the present study on the extent of circumference of shoot axis, cortex area, pith, xylem area, fibre length, and the number of stomata /field of Abutilon indicum G.Don, Croton sparsiflorus Morong and Cassia occidentalis Linn has clearly indicated that air pollutants emitted from the clay industry and automobile exhaust exercised a decisive influence on the above parameters. The statistical analysis also corroborated the same.

Keywords: Air Pollutant, Particulate Matter, Shoot Axis, Vessels, Stomata

Introduction

The effects of agricultural, industrial and technological changes on our environment during the last century have been tremendous. The living cells undergo many physical and biochemical processes of growth; which exist with in a narrow range of factors such as temperature, light water and nutrients. Air pollution is a social disease, a disease generated primarily from the activities of man, adversely affecting his health and welfare (Gilette, 1984). Pollution stress can alter plant growth and quality and the effects are often extensive (Sagar et al., 1982). We are facing the fact that in relatively recent times, the total amount and complexity of toxic pollutants in the environment are increasing day by day. Stratmann & Van Haut (1966) dusted plants with quantities of dust ranging from 1 to 48 g/m2 per day; dust falling on the soil caused a shift in pH to the alkaline side, which was unfavorable to oats but favorable to pasture grass. Darley et al. (1966) noted that plants were stunted and had few leaves in the heavily dusted portions of an alfalfa field downwind from a cement plant in California. Brandt & Rhoades (1972) observed significant changes in structure and composition of the seedling, shrub, sapling, and tree strata when they compared dusted and non dusted forest communities in the vicinity of limestone quarries and processing plants.

Considerable reduction in pigment (chlorophyll a, chlorophyll b and carotenoids) and sugar contents were observed at sites receiving higher pollution load. Ascorbic acid exhibited significant positive correlation with pollution load (Atul and Tripathi, 2009). The incremental concentrations of pollutants depend on the energy balance in the atmosphere, which determines the stability and turbulence (both thermal and mechanical), and the thickness of the mixing layer (Turtos et al., 2008). The influence of meteorological conditions on air quality deterioration is widely studied subject. The local climate aroundá an industry has a lot to do with the air pollution (Turtos et al., 2009).

The plants growing in polluted environment often show symptoms of various injuries, decibility and premature ageing. Various pollutants like SO2, CO2, N2O, NO, HF, chlorine and particulate matter discharged into atmosphere from automobiles, various factories and power stations. These pollutants cause serious injuries internally as well as externally to plants and plant cells. A perusal literature reveals that there is little information on the effect of air pollutants on plant tissues. Hence the present study is undertaken with a view to record the effects of air pollution on various tissue systems of Abutilon indicum, Croton sparsiflorus andCassia occidentalis.

Materials and Method

The present study has been carried out at S.N. College Campus at Kollam district, Kerala, India as control site and Kochuveli in Thiruvananthapuram district, Kerala, India as polluted site at a distance 60 km from the control site. English Indian Clays (PVT) Ltd. Industrial complex is situated at Kochuveli, Thiruvananthapuram. China clay is being used in the factory as the raw material. The production capacity of the company is one-lakh metric tones. The main waste product is silica sand. White clay is spreading during the clay drying process and clings on the surrounding vegetation. Automobile exhausts mainly from the clay transporting trucks also contributing much to the air pollution in the area.

The plant species used for the study is Abutilon indicum, Croton sparsiflorus and Cassia occidentalis. The samples were collected with the help of chisel and hammer. The third internodes are taken for study. Leaves from plant were collected and the number of stomata /field was recorded from the lower epidermis. Soon after collection, the samples were fixed in the FAA on the spot itself. The materials were kept in the fixative for a week. After one week the fixed materials were transferred to Alco-Glycerol mixture for preservation and softening.

The wood samples were macerated to obtain vessel segments and fibers. Fixed samples were sliced tangentially at a thickness of about 1 mm. The slices were treated first with distilled water and then with 40% HNO3 till the elements got free from each other. The macerated elements were washed and stained and mounted in 5% glycerol for microscopic study. Radius of different regions of the cross section of the samples and length and width of vessels (after maceration, staining and mounting) were measured with the help of ocular micrometer scale under the compound microscope.

After softening, the fixed materials were washed thoroughly in running water and were sectioned in a sliding microtome at a thickness of 20µm. Heiden Lain Iron Haematoxylene and Bismark Brown method is used for staining.

Results

The data pertaining to Abutilon indicum, which shows a significant reduction in circumference of the shoot axis and the xylem area in the polluted samples. Cortex and pith areas did not show any significant variation between the control and polluted samples. Vessel length was found to vary from 244.8µm to 340µm in the control and from 258.8µm to 353.6µm in the polluted samples. The mean values were 290µm and 299µm in the control and polluted samples respectively. The vessel width ranges from 34 to 68µm with an average value of 44µm in the control and from 34µm to 81.6µm with an average value of 51µm in the polluted samples. The fiber length varied from 816µm to 1740µm with an average value of 1169µm and from 1088µm to 1564µm with an average value of 1251µm in the control and polluted sites respectively. The average value recorded for the number of vessels /mm² were 85.93 in the control and 62.5 in the polluted samples and those for stomata / field were 30 in the control and 33 in the polluted samples (Table 1-2).

The data collected on Croton sparsiflorus shows a significant reduction in circumference of shoot axis and xylem area occurred in polluted samples. The cortex and pith areas do not show much variation between the control and the polluted samples. Vessel length ranged from 272µm to 435.2µm with an average value of 367.2µm in the control samples and from 231.2µm to 408µm with an average of 312.8µm in the polluted samples. The ranges of vessel width were from 34µm from 54.4µm with a mean value of 44.88µm and from 27µm to 54.4µm with mean value of 36.72µm in the control and the polluted samples respectively. The fiber length was found to vary from 448.8µm to 707.2µm with an average of 561.95µm in the control samples and from 380.8µm to 680µm with an average value of 530µm in the polluted samples. The average values recorded for the number of vessels /mm² and the number of stomata / field were 101.56 and 38 respectively in the control samples and the corresponding values of the polluted samples were 140.62µm and 50µm. The statistical analysis showed a significant increase in the number of vessels /mm² and in the number of stomata /field. Conversely, the vessel length and vessel width underwent a decrease to a highly significant level in the polluted samples. The variations in the vessel area and fiber length between the control and the polluted samples remained statistically insignificant (Table 3-4).

The data collected on Cassia occidentalis exhibits a significant reduction in the circumference of shoot axis and xylem area in the polluted sample. But the cortex area and the pith did not show any significant variation between the control and the polluted samples. Vessel length varied from 163µm to 394µm with an average value of 335µm in the control and from 204µm to 394µm with an average value of 299µm in the polluted sample. The width of the vessel varied from 27µm to 47µm with an average value of 46µm and from 27µm to 60µm with an average of 57µm in the control and polluted samples respectively. The fibre length was found to vary between 530µm to 1292µm in control and from 544µm to 1428µm in the polluted samples. Their average value of fibre length was 829µm and 848µm in the control and polluted samples respectively. The mean values of number of vessels/mm²and number of stomata/ field were 57 and 65 respectively in the control and 64 and 79 in the polluted samples. The statistical analysis revealed a highly significant reduction in vessel length in the polluted sample. However the vessel width, vessel area, number of vessels /mm² and the number of stomata / field are increased to a highly significant level under the influence of air pollutants. The fiber length did not shown significant variation (Table 5-6).

Discussion

The effects of air pollutants on various anatomical traits have been studied by various workers in India and abroad. Impact of gaseous and particulate pollutants on anatomical features was studied by Wang and Wieger (1986). It is evident from the table that a highly significant increase in the fiber length and vessel width occurred in the polluted atmosphere. However, the number of vessels /mm² decreased to a highly significant level in the polluted sample. Besides, a reduction in the vessel area was also found in the polluted sample. The variation in the number of stomata /field was found to be significant only at 5% level. The variation in the vessel length was not significant.

It is well conceived fact that the pollutants reduce wood formation in timber trees and yield in crop plants. The air pollutants like particulate matter from the clay factory and automobile exhaust from transporting trucks cause severe threat to the vegetation. The significant decreases in the circumference of the shoot axis due to low rate of xylem production under the influence of air pollutants were observed. A similar observation has been recorded earlier in case of some timber trees (Ghouse et al., 1984; Khan et al., 1993; Holopainen et al., 2000).

However the extent of tissue systems viz. cortex and pith remained statistically unaffected and seem to be resistant to air pollutants. But contrary to this the vessel length in Abutilon indicum is not affected by the pollutants. In the present study, increase in vessel width was observed. It is in conformity with the observations made by Khan et al., 1993 and Holopainen et al., 2000. Occurrence of intrusive growth in vessel segments and fibre elements showed a high percentage in polluted samples of Abutilon indicum. This perhaps accounts for the overall increase in length average of these elements in the polluted samples of this plant species.

The vessel length decreased significantly as reported earlier in case of some weeds (Ghouse and Khan, 1983) and in Polygonum glabrum (Khan et al., 1984). The present data revealed that the fiber length remained unaffected by the air pollutants. A reduction in stomatal number was recorded as influence of air pollutants in Callistimone citrinus (Zaidi et al., 1980). In the contrary to this the number of stomata increased significantly in the polluted samples. Possibly this may be one of the adaptive features to reduce the damage caused by clay dusting.

A significant loss of assimilatory organs and wood in conifers growing in regions loaded by air pollutants was noticed by Konopka et al (1997).While studying the biochemical defense mechanism of plants Srivastava (1999) noticed that some of the atmospheric gases at their supra optimum level, become pollutant and evoked various types of visible plant responses which ultimately lead to reduced growth and reproductively.

The different tissues of the same plant differ in their responses to the same pollutant. A statistical analysis of the data obtained from the study showed a significant reduction in circumference of shoot axis and xylem area of the plants. But cortex and pith areas did not show any significant variation between the control and the polluted samples.

Pollutants emitted from the industry and automobile exhaust exercised a decisive influence on plant anatomy. The statistical analysis also corroborated the same. From the present data it is also become apparent that the vessel elements are affected more in size and proportion compared to other elements. In other words vessels are more sensitive to pollutants. The different tissues of the same plant differ in their responds to the same pollutant. Further, the different genetic constitutions differ in their responds to the same pollutants in a given concentration.

Summary

It can be concluded that the particulate matter pollution had significantly affected the anatomical structures of tropical plants. The effects of Particulate pollution could affect the transport system within the plant and productivity. The vessel elements of plants are more prone to the particulate pollution. The number of stomata was increased in plants to cope up with the stress condition. It can be recommended that proper measures to be taken to reduce the particulate matter in industries to decrease the damage to the plants.

Table 1 · Data on the anatomical changes due to air pollution in Abutilon indicum
N║ Parameters Control Polluted t-test Table value of t
Mean ± SD Mean ± SD 1% 5%
1 Circumference (mm) 10 ± 7.954 8.2 ± 3.17 2.768 4.604 2.776
2 Cortex area (mm) 0.58 ± 0.312 0.6 ± 0.382 1.891 4.604 2.776
3 Xylem area (mm) 4.7 ± 0.517 3.3 ± 0.443 2.977 4.604 2.776
4 Pith area (mm) 1.7 ± 0.701 1.36 ± 0.756 1.761 4.604 2.776
5 Number of vessels / mm² 85.93 ± 4.121 62.5 ± 3.981 4.054 2.704 2.021
6 Vessel length (µm) 290 ± 10.784 299 ± 9.485 0.625 2.704 2.021
7 Vessel width (µm) 44 ± 2.614 51 ± 2.6706 4.092 2.704 2.021
8 Vessel area mm² 0.56 ± 3.326 0.29 ± 0.236 3.326 4.604 2.776
9 Fiber length (µm) 1169 ± 57.89 1251 ± 38.497 5.868 2.704 2.021
10 Number of stomata/field 30 ± 1.2207 33 ± 1.0266 2.564 2.704 2.021
** Significant at 1%, * Significant at 5%, NS-Non significant
Table 2 · Percentage Variation caused by air pollution in Abutilon indicum
N║ Parameters Abutilon indicum
1 Circumference (mm) 26.52
2 Cortex area (mm) 7.5
3 Xylem area (mm) 17.77
4 Pith area (mm) 22.4
5 Number of vessels / mm² -38.46
6 Vessel length (µm) 14.81
7 Vessel width (µm) 18.18
8 Vessel area mm² 48.35
9 Fiber length (µm) 5.68
10 Number of stomata/field -32.24
Table 3 · Data on the anatomical changes due to air pollution in Croton sparsiflorus
N║ Parameters Control Polluted t-test Table value of t
Mean ± SD Mean ± SD 1% 5%
1 Circumference (mm) 17 ± 3.476 12.49 ± 2.182* 2.977 4.604 2.776
2 Cortex area (mm) 16 ± 0.17 0.085 ± 0.0382 NS 1.821 4.604 2.776
3 Xylem area (mm) 4.5 ± 0.565 3.7 ± 0.455 3.821 4.604 2.776
4 Pith area (mm) 0.58 ± 0.151 0.45 ± 0.09 NS .164 4.604 2.776
5 Number of vessels / mm² 101.56 ± 7.849 140.62 ± 27.6** 5.143 2.704 2.021
6 Vessel length (µm) 367.2 ± 12.476 312.6 ± 14.372** 4.248 2.704 2.021
7 Vessel width (µm) 44.88 ± 1.907 36.72 ± 2.082** 4.7 2.704 2.021
8 Vessel area mm² 0.91 ± 0.79 0.47 ± 0.275 1.85 4.604 2.776
9 Fiber length (µm) 561.95 ± 15.953 530 ± 20.78 NS 1.913 2.704 2.021
10 Number of stomata/field 38 ± 0.911.355 50 ± 1.4456** 5.778 2.704 2.021
** Significant at 1%, * Significant at 5%, NS-Non significant
Table 4 · Percentage Variation caused by air pollution in Croton sparsiflorus
N║ Parameters Croton sparsiflorus
1 Circumference (mm) 18
2 Cortex area (mm) -2
3 Xylem area (mm) 29.78
4 Pith area (mm) 20
5 Number of vessels / mm² 27.26
6 Vessel length (µm) -3.1
7 Vessel width (µm) -15.9
8 Vessel area mm² 48.21
9 Fiber length (µm) -7.01
10 Number of stomata/field -10
Table 5 · Data on the anatomical changes due to air pollution in Cassia occidentalis
N║ Parameters Control Polluted t-test Table value of t
Mean ± SD Mean ± SD 1% 5%
1 Circumference (mm) 16.9 ± 2.815 12 ± 2.12* 2.737 4.604 2.776
2 Cortex area (mm) 0.27 ± 0.227 0.26 ± 0.182 NS 1.688 4.604 2.776
3 Xylem area (mm) 5.2 ± 0.647 3 ± 0.849* 2.954 4.604 2.776
4 Pith area (mm) 4.6 ± 1.16 4.2 ± 0.166 NS 0.270 4.604 2.776
5 Number of vesselsá/ mm² 57 ± 7.849 64 ± 27.6** 5.04 2.704 2.021
6 Vessel length (µm) 335 ± 11.536 299 ± 12.815** 3.038 2.704 2.021
7 Vessel width (µm) 46 ± 2.73 57 ± 3.58** 3.85 2.704 2.021
8 Vessel area mm² 0.42 ± 0.27 0.3516 ± 0.73** 4.821 4.604 2.776
9 Fiber length (µm) 829 ± 46.411 848 ± 34.03 NS 1.739 2.704 2.021
10 Number of stomata/field 65 ± 2.5278 79 ± 2.115** 5.5818 2.704 2.021
** Significant at 1%, * Significant at 5%, NS-Non significant
Table 6 · Percentage variation caused by air pollution in Cassia occidentalis
N║ Parameters Cassia occidentalis
1 Circumference (mm) 28.9
2 Cortex area (mm) 3.7
3 Xylem area (mm) 42.3
4 Pith area (mm) 8.69
5 Number of vessels / mm² -12.28
6 Vessel length (µm) 10.75
7 Vessel width (µm) -23.9
8 Vessel area mm² 16.28
9 Fiber length (µm) 2.29
10 Number of stomata/field -21.5

Acknowledgement

I acknowledge with gratitude the help and support from University Of Kerala, Prof. & Head, Department of Environmental Sciences, University of Kerala.

References

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