Effect of 3-hour fumigation with 1.0, 0.5, 0.09 and 0.04 ppm concentration of sulphur dioxide on the leaves of 15 and 30-day old plants of Trigonella foenum-graecum were studied under laboratory conditions. The parameters used to assess the effects were chlorophyll contents and leaf area damage of fumigated plants. Since it was noticed that leaves of different ages responded differently, three size classes of leaves were studied separately.

INTRODUCTION

Leaf injuries of different types and of varying intensities caused by industrial effluents have been recorded by Chaphekar1 in Bombay city. The extent and type of injury caused to leaves exposed to different concentrations of sulphur dioxide have been reported by many workers, Brandt and Heck2 David8, Banerjee and Chaphekar4 and Boralkar and Chaphekar5 reported injury to many plants due to SO2.

MATERIALS AND METHODS

Seeds of Trigonella foenum-graecum L. obtained from an authorised seed dealer were sown in 20 cm diameter earthen pots containing especially prepared soil comprising red laterite loam-90% and farmyard manure-10%. After 8 days, thinning was done, keeping 10 plants per pot. Plants of five pots for each concentration were exposed to 1.0, 0.5, 0.09 and 0.04 ppm SO2 for 3 hours separately, in a fumigation chamber, Banerjee, et al6. After a period of 24 hr, estimations for total chlorophyll, chlorophyll a, and chlorophyll b were done by following the methods of Anion7, also measurements of injured leaf area was made, using transparent graph papers. Leaves were grouped on the basis of size into small (< 50 mm2), medium (51 to 100 mm2) and large (> 100 mm2) for the assessment of injury at different ages of leaves.

RESULTS AND DISCUSSION

From the results of leaf area injury as given in in Tables 1 and 2, it is apparent that the extent of injury of 15-day old plants at 1.0 ppm was 83%, which decreased at decreasing concentrations. Similarly, the leaf area injury of 15-day old medium leaves at 1.0 ppm was 81% and that at 0.5 ppm it was 40%). At 0.09 and 0.04 ppm concentration, the leaf area injury was 31 and 23.5% respectively. In the case of 15-day old large leaves the leaf area injury was 56% at 1.0 ppm and 37, 20.5 and 14% at 0.5, 0.09 and 0.04 ppm, respectively. The total leaf area injury of all 15-day old leaves was 78.2% at 1.0 ppm, 42% at 0.5 ppm, 20.4% at 0.04 ppm and 20.6% at 0.09 ppm concentration. Thus, the small leaves of 15-day old T. foenum-graecum plants showed maximum leaf injuries at all SO2 concentrations as compared with those of medium and large sized leaves.

Injuries to small leaves of 30-day old plants at 1.0 ppm was 42% and at 0.5 and 0.09 ppm 35 and 21% respectively. The leaf area injury for 30-day old medium leaves at 1.0, 0.5, 0.09 and 0.04 ppm concentrations were 31, 17 and 14%, respectively. Similarly, the large leaves of 30-day old plants had leaf area injury of 20% at 1.0 ppm concentration and 18.9, 16.5 and 13% at 0.5, 0.09 and 0.04 ppm concentrations, respectively. It is seen from the above results that small leaves

Table 1 : Effect of a 3-hour SO2 fumigation at 1.0,0.5, 0.09, and 0.04 ppm concentrations on leaf are injury and chlorophyll contents of 15-day old Trigonella foenum-graecum plants.

SO2 Concentration(ppm)	Leaf Area Injury (%)	Chlorophyll (mg/g fresh weight)		Chlorophyll a/b
	Large (100mm2) & more	Medium (51 to 100 mm2)	Small (less than 50mm2)	Total	Total	a	b
1.0	56	81	83	0.956	0.591	0.350	1.6
0.5	37	40	80	1.61	0.879	0.695	1.2
0.09	20.5	31	66	3.32	1.59	1.62	0.9
0.04	14	23.5	46	6.25	3.21	2.87	1.1
Contorl	-	-	-	6.65	3.22	3.89	0.95

Table 2 : Effect of a 3-hour SO2 fumigation at 1.0, 0.5, 0.09 and 0.04 ppm concentration on Leaf are injury and chlorophyll content of leaves of 30-day old plants of Trigonella foenumgraecum.

SO2 Concentration(ppm)	Leaf Area Injury (%)	Chlorophyll (mg/g fresh weight)		Chlorophyll
	Large (> 100mm2)	Medium (51 to 99 mm2)	Small (< 50 mm2)	Total	Total	a	b	a / b
1.0	20	31	42	28	6.04	2.11	3.69	0.5
0.5	18.9	30	35	25.3	7.99	3.42	4.28	0.79
0.09	16.5	17	21	17.5	8.50	3.66	4.55	0.8
0.04	13	14	17	14.4	9.71	3.91	5.42	0.72
Contorl	-	-	-	-	9.92	4.00	5.54	0.7

of 30-day old Trigonella foenum-graecum plants showed maximum injury at all concentrations of SO2. Medium leaves showed injury above 30% at 0.5 and 1.0 ppm concentrations.

It may be concluded from the above that 15-day old plants were more susceptible to SO2 than the 30-day old ones, and the small leaves of 15-day old plants showed maximum injury at all SO2 concentrations as apparent by the injury index values which were more in 15-day plants than in the 30-day old plants.

The total chlorophyll content in 15-day old leaves exposed to 1.0 ppm SO2 was 0.956 mg/g fresh weight but the same continuously increased at decreasing levels of S02. The control leaves of 15 and 30-day ages had the total chlorophyll contents of 6.65 and 9.92 mg/g fresh weight respectively. The 15-day old leaves suffered a higher loss of chlorophyll than the 30-day ones, at all levels of SO2 exposure.

The degradation of chlorophyll a into phaeophytin a has been reported by Rao and LeBlanc8. This degradation process is initiated by H2SO3 at low pH of 2.3. In the present study perhaps the reduction of total chlorophyll was due to such degradation of chlorophyll. It was noticed that the injury to individual chlorophyll pigment was not selective at lower SO2 concentrations, at both the ages of plants tested. At concentrations of 0.5 and 1.0 ppm however, the a/b ratio went on increasing gradually in younger plants, indicating higher loss of chlorophyll b.

CONCLUSION

The Trigonella foenum-graecum L. plants were found sensitive to SO2 fumigation at 1.0, 0.5, 0.09 and 0.04 ppm concentrations for three hours at 15 and 30-day ages. The 15-day old plants were more sensitive than the 30-day old ones. The leaf area injury and chlorophyll loss increased at increasing SO2 concentrations. The leaf area injury was greater in younger than older leaves.

ACKNOWLEDGEMENTS

The authors are grateful to the University Grants Commission, New Delhi, for financial support and to Prof. B.C. Haldar, Director, and Dr. V. D. Tilak Head of the Botany Department of Institute of Science, Bombay, for encouragement to carry on this research.

REFERENCES

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