J. Environ. Res. Develop. Journal of Environmental Research And Development Vol. 8 No. 2, October-December 2013

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1 TOXIC EFFECT OF HEAVY METALS ON GERMINA- TION AND SEEDLING GROWTH OF WHEAT Gang A., Vyas A. 1 and Vyas H.* 2 1. S. S. in Microbiology, Vikram University, Ujjain, Madhya Pradesh (INDIA) 2. Department of Botany, Govt. Kalidas Girls College, Ujjain, Madhya Pradesh (INDIA) Received June 1, 213 Accepted Novembert 7, 213 ABSTRACT Heavy metal pollution is one of the major environmental problems of the present century. It is mainly due to the anthropogenic activities. Many industries, including metallurgy, electroplating, paints and pigments industries, tanning, wood preservation, chemical industries and pulp and paper producing industries use various heavy metals and discharge from these industries largely contribute to heavy metal pollution. Land disposal of wastes/effluents containing heavy metals contaminate soil ecosystem and once present in the soil the metals are persistent. Although living organisms require metals for their growth but at high concentration they become toxic to plants and animals. India is primarily an agriculture based country and if crops are grown on soil containing high amount of heavy metals then their growth will be adversely affected. Wheat is the main food crop of India and we wanted to study the effect of different heavy metals on its germination and seedling growth. In this paper the effect of copper, chromium and cobalt on seed germination, root and shoot growth of wheat is described. Our results show that seed germination and root and shoot growth is significantly reduced at high concentrations of all the three heavy metals. Key Words : Heavy metals,,,, Wheat, Germination, Seedling growth INTRODUCTION Soil contains trace levels of many heavy metals and most of these heavy metals are essential elements for living organisms, but their excess amount is generally harmful to plants, animals and human health. 1-3 Many anthropogenic activities pollute the soil ecosystems with heavy metals resulting in conditions which are toxic for living organism. 4,5 Soil contamination by industrial effluents loaded with toxic heavy metals has raised a new threat to agriculture. These effluents and wastes contain heavy metals in sufficient amount to cause toxicity to crop plants. Excessive accumulation of heavy metals like copper, cobalt, chromium, nickel, cadmium, zinc etc. in soil as a result of mining, processing and other technological activities of man have been reported. 6-8 There are several studies emphasizing the influence of heavy *Author for correspondence 26 metals such as Ni, Co, Cu, Mn and Zn on plant growth and function. 4,6,9,1 However, underlying all these studies, there is a requirement to expose plants to toxic, but appropriate, concentration of the trace metal in order to study heavy metal tolerance in plants. 9 India is an agriculture based country and wheat is one of the major cereal crop grown in India. India is the world's second largest producer of wheat. 11 Thus, it is important to study the toxicity of heavy metals on this crop. We have selected three heavy metals namely Cu, Co and Cr and studied their phytotoxicity on wheat. Cu is an essential micronutrient for growth of plants and animals, 12,13 whereas Co and Cr are non-essential for plants but they are essential for humans, animals and microorganisms. 6,14,15 These heavy metals are toxic to living organisms when present at high concentrations. 5,16-18 is one of the common heavy metals in industrial discharge

2 of aeronautics, metal and metallurgy and refinery industries showing toxic effects on plants and animals. 1,5 has a widespread use in several industrial applications such as production and refining of alloys, jet engines, gas turbines and electrochemical materials. 19 is also used in varnishes, paints, catalysts, inks, pigments, ceramics and surgical implants and shows toxic effects at high concentration. 17 is used on a largescale in many industries, including tanning, metallurgy, electroplating, production of paints and pigments, chemical production and pulp and paper production. These industries cause significant Cr pollution and results in adverse biological and ecological effects. 2,21 Keeping in view the importance of wheat as major food crop and the excessive use of copper, cobalt and chromium in various industries the present study has been designed to study the effect of different concentrations of these heavy metals on germination and seedling growth of wheat. AIMS AND OBJECTIVES To determine the effect of different heavy metals on seed germination and seedling growth of wheat (Triticum aestivum L., Var. GW-366). The study had following objectives 1. To study the effect of different concentrations of copper, cobalt and chromium on seed germination and seedling growth of wheat. 2. To determine the percentage phytotoxicity of copper, cobalt and chromium on wheat. MATERIAL AND METHODS Seed germination Wheat (Triticum aestivum L., Var. GW-366) seeds for the experiments were obtained from Agriculture Science Farm, Vikram Nagar, Ujjain, Madhya Pradesh, India. The seeds were stored at room temperature in air tight packets. Ten different concentrations viz..1, 1, 5, 1, 5, 1, 2, 3, 4 and 5 ppm were prepared from stock solution (1 ppm) of copper sulphate (CuSO 4.5H 2 O), cobaltous sulphate (CoSO 4.7H 2 O) and potassium 27 chromate (K 2 CrO 4 ). Distilled water was used as control. The seeds were surface sterilized by immersing the seeds in.1% HgCl 2 solution for one to two minutes to avoid surface fungal and bacterial contamination. 22 Seeds were rinsed with sterile distilled water three times and blotted on sterile filter paper. Twelve healthy and uniform sized seeds of wheat were selected for germination test in sterilized petridishes. The seeds placed in petridish were equally spaced from each other and 1 ml of test solution was added to each petridish. The petridishes were kept moist by regularly adding 5 ml of test solution if required and incubated at 25 ± 2 o C. The experiment was carried out in triplicate. Seed germination was recorded after 24 hours of incubation and percentage germination was calculated. Seedling growth The experimental set up was as described above. The seedling growth was monitored after two, four and six days. The root length and shoot length were measured and dry weight of root and shoot were determined. Root length was measured from the main apex to the crown whereas shoot length was measured from the crown to the main apex. 1 For determining the dry weight of root and shoot, the excess water was blotted from the plant material using filter paper and then the samples were kept in oven at 8 ο C for two hours and weight was measured using electronic balance. Percentage phytotoxicity Percentage phytotoxicity of copper, cobalt and chromium on root and shoot growth was calculated after six days of seedling growth. The following formula was used for calculating the percentage phytotoxicity. % Phytotoxicity = S/R length of control - S/R length of treatment S/R length of control x 1 S/R= Shoot or root Statistical analysis Statistical analysis was performed using two way analysis of variance (ANOVA) followed

3 by Tukey s HSD test. P value.1 was considered as significant. RESULTS AND DISCUSSION Effect of heavy metals on seed germination Effect of different concentrations (.1, 1, 5, 1, 5, 1, 2, 3, 4 and 5 ppm) of three heavy metals namely copper, chromium and cobalt was studied on germination percentage of wheat seeds (Triticum aestivum L., Var. GW-366). Distilled water without any heavy metal was used as control. The results show that (Fig. 1) as the concentration of heavy metals was increased there was reduction in germination percentage over control but the differences were not significant upto 1 ppm concentration of heavy metals (Cu, Co and Cr). However, all the three heavy metals significantly reduced germination in comparison to control at 2-5 ppm concentrations (P.1). has minimum toxic effect on germination of wheat seed as even at 5 ppm chromium about 72% of the seeds germinate, while at 5 ppm copper and cobalt, seed germination is 54% and 44% respectively (Fig. 1) where as in control 97-1% seeds germinate. % Germination Fig. 1 : Effect of heavy metals on seed germination in wheat Earlier workers have also shown that heavy metals affect seed germination in plants. The reduction in seed germination by cobalt, copper and chromium has also been studied in chickpea, 6 alfalfa plant 13 and corn. 3 The effect of chromium on germination of different varieties of wheat was studied by Datta et al. 22 who found that in all the five wheat varieties studied by them the germination is about 65-8% at 1 ppm. Mahmood et al., 4 studied the effect of 1 to1 ppm copper on wheat (Triticum aestivum L.) and found that at 1 ppm copper (1µM), there is more than 35% reduction in seed germination whereas we have studied the effect of.1-5 ppm copper and our results show that at 1 ppm copper there is no significant reduction in seed germination in wheat (Triticum aestivum L., 28 Var. GW-366), this indicates that varieties of wheat may differ in tolerance to high amount of copper. Singh et al. studied the effect of 5-1 ppm (mg/l) copper on wheat seed (Triticum aestivum L., Var. - PBW 343) and found that at 1 ppm copper the germination of seeds is about 65%, 5 whereas our study shows about 82% seed germination in wheat (Triticum aestivum L., Var. GW-366) which again points out that some varieties may be more resistant to high metal concentrations. However, both the above mentioned studies show that high amount of copper reduces the germination percentage in wheat which corroborate with our results, but it also points out that we should search for varieties which can resist and grow better at high metal concentrations.

4 Effect of heavy metals on root growth Fig. 2 shows the effect of different concentrations of heavy metals on root growth of wheat after 6 days. A, B and C represent copper, cobalt and chromium respectively and subscript represents concentration of heavy metals in ppm. The effect of different concentrations of heavy metals on root length and root weight after six days of growth is shown in Fig. 3 and Fig. 4 respectively. Similar trend was seen after two and four days of growth. The results show that there is significant reduction in root length over control at 1 ppm and above concentrations of chromium (P.1) while significant reduction in root length over control is seen at 5 ppm and above concentrations of copper and cobalt (P.1). Fig. 2 : Wheat seeds growing at different concentrations of heavy metals after 6 days of growth Significant reduction in root weight over control is seen at 5 ppm and above concentrations of copper, cobalt and chromium (P.1). The effect of heavy metals on root growth has been studied in corn, 3 alfalfa plant, 13 Brassica juncea, 18 6,23,24 chickpea and Arabidopsis thaliana Datta et al. 22 studied the effect of chromium on root length of different varieties of wheat 29 and showed that at 1 ppm concentration of chromium root growth is completely inhibited, whereas our results show 86% reduction in root length at 1 ppm concentration of chromium. The effect of copper on root length of wheat (Triticum aestivum L.) has been studied by Mahmood et al., 4 who found that at 1 ppm copper (1µM), there is about 7% reduction in root

5 length whereas our results show that at 1 ppm copper there is no significant reduction in root length in wheat (Triticum aestivum L., Var. GW-366). Thus, it appears that different varieties of wheat differ in their tolerance level to heavy metals. Root length (cm) Fig. 3 : Effect of Cu, Co and Cr on root length of wheat after 6 days of growth Root weight (g) Fig. 4 : Effect of Cu, Co and Cr on weight of root after 6 days of growth Effect of heavy metals on shoot growth The effect of different concentration of copper, cobalt and chromium on shoot length and dry weight of shoot after 6 days of growth is shown in Fig. 5 and Fig. 6 respectively. Similar trends were seen after two and four days of growth. It can be seen that there is significant reduction in shoot length over control at 5 ppm and above concentrations of all the three metals (P.1) and significant reduction in shoot weight over control at 1 ppm and above concentrations of chromium (P.1) and 5 ppm and above concentrations of copper and cobalt (P.1). The effect on shoot growth due to heavy metals has been studied in rice, 4 barley, 4 melon, 14 corn 3 and chickpea. 6 The effect of copper on shoot length of wheat (Triticum aestivum L.) 21 has been studied by Mahmood et al., 4 who found that at 1 ppm copper (1µM), there is about 42% reduction in shoot length whereas our results show that at 1 ppm copper there is increase in shoot length as compared to control in wheat (Triticum aestivum L., Var. GW-366), showing that the plant require a trace amount of copper for its growth. Datta et al. 22 studied the effect of chromium on shoot length of different varieties of wheat and showed that at 1 ppm concentration of chromium shoot growth is 6-7% reduced, whereas our results show 53.9% reduction in shoot length at 1 ppm concentration of chromium. Thus, there is marked variation in tolerance to heavy metals in different wheat varieties.

6 Shoot length (cm) Fig. 5 : Effect of Cu, Co and Cr on shoot length after 6 days of growth Shoot weight (g) Fig. 6 : Effect of Cu, Co and Cr on weight of shoot after 6 days of growth Percentage phytotoxicity The percentage phytotoxicity of different heavy metal on root length and shoot length of wheat was calculated and results are shown in Fig. 7 and Fig. 8. It can be seen that percentage phytotoxicity on root length at 5 ppm copper and 5 ppm chromium is about 72% and 6% respectively, while percentage phytotoxicity in root length at 5 ppm cobalt is about 23%. The percentage phytotoxicity on root length of wheat is 93-95%, 85-97% and 95-96% at 3-5 ppm concentrations of copper, cobalt and chromium respectively (Fig.7). Thus at lower concentration cobalt is least toxic while at high concentration it % phytotoxicity shows maximum toxicity on root length. There is decrease in phytotoxicity of copper on shoot length from -1 ppm showing that it is essential trace element for the growth of wheat (Fig. 8). The percentage phytotoxicity of copper, cobalt and chromium on shoot length of wheat at 5 ppm is about 31%, 32% and 4% respectively. The percentage phytotoxicity of copper on shoot length of wheat is about 91% at 5 ppm concentration, whereas at 5 ppm concentration percentage phytotoxicity of cobalt and chromium is 83 and 87% respectively (Fig. 8). Thus all the three heavy metals have almost equal toxic effect on shoot growth. Fig. 7 : Percentage phytotoxicity of Cu, Co and Cr on root length of wheat

7 % Phytotoxicity Fig. 8 : Percentage phytotoxicity of Cu, Co and Cr on shoot length of wheat CONCLUSION Present study reveals that high concentrations of copper, cobalt and chromium can significantly reduce germination percentage and can adversely affect seedling growth of wheat (Triticum aestivum L., Var. GW-366). Comparison with previous studies indicates that varieties of wheat may differ with respect to tolerance of heavy metals and we should search for varieties of wheat which can resist and grow better at high metal concentrations. However, further studies are needed to test, if these heavy metals enter the food chain even when the growth of wheat is not drastically effected. ACKNOWLEDGEMENT We gratefully acknowledge the financial assistance received from University Grants Commission, CRO, Bhopal [Project No. MS- 71/1724/11-12/CRO(2)] and University Grants Commission, New Delhi (India) [Project No. F.No /28(SR)] for supporting this research work. REFERENCES 1. Houshmandfar A. and Moraghebi F., Effect of mixed cadmium, copper, nickel and zinc on seed germination and seedling growth of safflower, Afri. J. Agric. Res., 6(5), , (211). 2. Azevedo R. and Rodriguez E., Phytotoxicity of mercury in plants : A Review, J. Bot., 11(5), 1-1, (212). 3. Mahmood S., Hussain A., Saeed Z. and Athar M., Germination and seedling growth of corn (Zea mays l.) under varying levels of copper and zinc, Int. J. Environ. Sci. Tech., 2 (3), , (25). 4. Mahmood T., Islam K. R. and Muhammad S., Toxic effects of heavy metals on early growth and tolerance of cereal crops, Pak. J. Bot., 39 (2), , (27). 5. Singh D., Nath K. and Sharma Y.K., Response of wheat seed germination and seedling growth under copper stress, J. Environ. Bio., 28 (2), , (27). 6. Khan M. R. and Khan M. M., Effect of varying concentration of nickel and cobalt on the plant growth and yield of Chickpea, Aust. J. Basic Appl. Sci., 4(6), , (21). 7. Chouhan Arti, Iqbal Sanjeeda, Maheshwari R. S. and Bafna A., Study of heavy metal accumulations and relative effects on total photosynthetic pigments in plant leaves growing in Pithampur industrial area sector- 1, 2 and 3, India, J. Environ. Res. Develop., 7(2A), , (212). 8. Joshi B. H. and Modi K. G., Screening and characterization of heavy metal resistant baeteria for it s prospects in bioremediation of contaminated soil, J. Environ. Res. Develop., 7(1A), , (213). 9. Kopittke P. M., Blamey F.P.C., Asher C. J. and Menzies N. W., Trace metal phytotoxicity in solution culture : A review, J. Experi. Bot., 61(4), , (21). 1. Ergun N. and Oncel I., Effects of some heavy metals and heavy metal hormone interactions on wheat (Triticum aestivum L. cv. Gun 91) seedlings, Afri. J. Agric. Res., 7(1), , (212). 11. Goncalves A. C., Nacke H., Schwantes D., Nava I. A. and Strey L., Phytoavailability of toxic heavy metals and productivity in wheat cultivated under residual effect of 212

8 fertilization in soybean culture, Wat. Air Soil Pollut., 7(1B), 69-73, (211). 12. Suriyanarayan S., Jessen G. Divya and Balasubramanian S., Effect of waste paper based industry effluents on the growth of tree seedlings, J. Environ. Res. Develop., 7(2A), , (212). 13. Aydinalp C. and Marinova S., The effects of heavy metals on seed germination and plant growth on alfalfa plant (Medicago sativa), Bulg. J. Agric. Sci., 15 (4), , (29). 14. Akinci I. E. And Akinci S., Effect of chromium toxicity on germination and early seedling growth in melon (Cucumis melo L.), Afri. J. Biotechnol., 9 (29), , (21). 15. Oliveira H., as an environmental pollutant : Insights on induced plant toxicity, J. Bot., 1(1), 1-2, (212). 16. Tripathi P. And Srivastava S., Mechanism to combat cobalt toxicity in cobalt resistant mutants of Aspergillus nidulans, Ind. J. Microbiol., 47(2), , (27). 17. Cakar Z. P., Alkim C., Turanli B., Tokman N., Akman S., Sarikaya M., Tamerler C., Benbadis L. and Francois J. M., Isolation of cobalt hyper-resistant mutants of Saccharomyces cerevisiae by in vivo evolutionary engineering approach, J. Biotechnol., 143(1), , (29). 18. Ghani A., Effect of chromium toxicity on growth, chlorophyll and some mineral nutrients of brassica juncea L., Egypt. Acad. J. biolog. Sci., 2 (1), 9-15, (211). 19. Stadler J.A. and Schweyen R.J., The yeast iron regulon is induced upon cobalt stress and crucial for cobalt tolerance, J. Biol. Chem., 277(2), , (22). 2. Zayed A. M. and Terry N., in the environment: factors affecting biological remediation, Plant soil, 249(2), , (23). 21. Shugaba A., Buba F., Kolo B. G., Nok A. J., Ameh D. A. and Lori J. A., Uptake and reduction of hexavalent chromium by Aspergillus niger and Aspergillus parasiticus, J. Pet. Environ. Biotechnol., 3(3), 119, (212). 22. Datta J. K., Bandhyopadhyay A., Banerjee A. and Mondal N. K., Phytotoxic effect of chromium on the germination, seedling growth of some wheat (Triticum aestivum L.) cultivars under laboratory condition, J. Agric. Technol., 7(2), , (211). 23. Li W., Khan M. A., Yamaguchi S. and Kamiya Y., Effects of heavy metals on seed germination and early seedling growth of Arabidopsis thaliana, Plant Growth Regul., 46(1), 45-5, (25). 24. Narian Kamini, Bhat Muzamil, Abhilash P. G. and Mohammad Y., Impact of distillery effluent on seedling growth and pigment concentration of Cicer arietinum L., J. Environ. Res. Develop., 6(3A), 61-68, (212). The struggle to save the global environment is in one way much more difficult than the struggle to vanquish Hitler, for this time the war is with ourselves. We are the enemy, just as we have only ourselves as allies. In a war such as this, then, what is victory and how will we recognize it? Al Gore 213