Two varieties of wheat (Triticum aestivum var. Blue Silver and T. aestivum var. Punjab 85) were tested for the phytotoxic eff ect of mercury on seed germination and seedling growth. Seed were treated with 25, 50, 75 and 100 ppm of HgCl2 solution. Both varieties showed enhanced seed germination at all levels of mercury compared to untreated control. However, shoot, root, and seedling length was signifi cantly (P<0.05) reduced in both wheat varieties at all the levels of mercury treatments particularly at 100 ppm of mercury. Th e highest reduction was observed in root length rather than shoot and seedling length. Th e tolerance indices for both varieties showed that that var. Blue Silver was more tolerant to mercury toxicity than var. Punjab 85

Mohammad Athar

Shagufta Naz Jamal

Zafar Iqbal

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41ORIGINAL SCIENTIFIC PAPERSummaryTwo varieties of wheat (Triticum aestivum var. Blue Silver and T. aestivum var. Punjab 85) were tested for the phytotoxic eff ect of mercury on seed germination and seedling growth. Seed were treated with 25, 50, 75 and 100 ppm of HgCl2 solution. Both varieties showed enhanced seed germination at all levels of mercury compared to untreated control. However, shoot, root, and seedling length was signifi cantly (P<0.05) reduced in both wheat varieties at all the levels of mercury treatments particularly at 100 ppm of mercury. Th e highest reduction was observed in root length rather than shoot and seedling length. Th e tolerance indices for both varieties showed that that var. Blue Silver was more tolerant to mercury toxicity than var. Punjab 85.Key wordsMercury toxicity; seed germination; plant growth; wheat varieties; Blue Silver; Punjab 85Agriculturae Conspectus Scientifi cus, Vol. 71 (2006) No. 2 (41-44)Evaluation of Two Wheat Varieties for Phytotoxic Eff ect of Mercury on Seed Germination and Seedling GrowthShagufta Naz JAMAL 1M. Zafar IQBAL 1Mohammad ATHAR 2( )1 Department of Botany, University of Karachi, Karachi 75270, Pakistan2 California Department of Food and Agriculture, 1220 N Street, Sacramento, CA 95814, USA e-mail: atariq@cdfa.ca.govReceived: March 31, 2006 | Accepted: June 22, 2006ACKNOWLEDGEMENTS This research was funded by a grant from the Faculty of Science, University of Karachi, which is gratefully acknowledged. Sincere thanks are expressed to Mr. Atiqur Rehman for his technical assistance during this research.Agric. conspec. sci. Vol. 71 (2006) No. 242 Shagufta Naz JAMAL, M. Zafar IQBAL, Mohammad ATHARIntroductionMercury is one of the best known toxic metals dis-charged from human activities. Th e global rise in mer-cury pollution by anthropogenic activities may have risen by three to four folds in this century, but the se-riousness of the problem at local levels is many times greater. Th e environmental protection agencies have ex-pressed increasing concern over the release of mercury to the environment in the past couple of years. Th ere are studies about the response of crop species to heavy metals reporting mechanisms that are responsible for their tolerance or sensitivity (Ernest 1996, Hall 2000, Mahmood et al. 2005, Shriapanahi and Anderson 1986, Vitorello et al. 2005, Watanabe et al. 2002, Williams et al. 2000). HgCl2 is dominant among all mercury forms. Shriapanahi and Anderson (1986) found elevated levels of cadmium, lead and mercury in the upper layer of soil following long term application of municipal wastewa-ter which resulted in the accumulation of toxic levels of these metals in the vegetables grown in these areas. Th e toxic eff ect of mercury on germination, growth and yield has been studied on diff erent plants (Mukherjee and De 1996, Varshney 1991, Vizarova et al. 1985).Wheat (Triticum asetivum L.) is the staple food for a large part of the world population including Pakistan. Wheat is grown in Pakistan on 8.141 million hectares with an average yield of 2.28 tons per hectare with a total production of 18.535 thousand tons (Agricultural Statistics of Pakistan 2003-2004). Th e average yield is below than most wheat producing countries like Germany (7.9 tons per hectare), France (6.6 tons per hectare) and Egypt (6.4 tons per hectare). With increasing popula-tion, the over-demanding production of wheat can be increased either by bringing more area under wheat cul-tivation or by introducing high yielding wheat varieties which are resistant against biotic and abiotic environ-mental stresses. Th e aim of this research is to investigate the eff ects of HgCl2 on seed germination and seedling growth of two varieties of wheat (Triticum asetivum var. Blue Silver and T. aestivum var. Punjab 85) commonly cultivated in Pakistan. Th e eff ect of mercury was tested at germination and seedling growth of wheat as these are the key events for the establishment of plants under any prevailing conditions.Materials and methodsHealthy seeds of two wheat varieties (Triticum ase-tivum var. Blue Silver and T. aestivum var. Punjab 85) were obtained from the Pakistan Agriculture Research Council, Karachi. Seeds were stored at room tempera-ture under air tight conditions before treatments with metal solution. Seeds were washed with distilled water and were placed on the fi lter papers in 90-mm diameter glass petri dishes. Each petri dish contained 20 seeds per treatment replicated three times. Mercuric chloride (HgCl2) solution was prepared as 25, 50, 75 and 100 ppm of Hg. Each Petri dish was supplied with 2 mL of mer-cury solution at alternate day replacing the old solution with the fresh solution. All the petri dishes were kept at room temperature (30 ± 2 0C) with 12 hourly light period provided by three mercury tubes (120W). Seed germina-tion, root, shoot and seedling length were recorded aft er 10 days and the data were analyzed statistically.ResultsTh e results showed that seed germination of both varieties was enhanced at all concentrations of mercu-ry as compared to untreated control (Table 1). Highest germination was observed at 25 ppm of HgCl2 treat-ment, 80% in var. Blue Silver and 70% in var. Punjab 85, respectively which was signifi cantly (P<0.05) diff er-ent from the control. Shoot length of both wheat varie-ties showed signifi cant results at diff erent treatments of mercury. Highest reduction in shoot length (5.80 cm) was observed in var. Blue Silver at 75 ppm of mercury which was signifi cantly (P<0.05) diff erent as compared to control (11.26 cm). At 75 and 100 ppm of mercury, the diff erence in shoot length in var. Blue Silver was Triticum aestivum var. Blue Silver Triticum asetivum var. Punjab 85  Treatments Seed germination (%) Shoot length (cm) Root length (cm) Seedling length (cm) Seed germination (%) Shoot length (cm) Root length (cm) Seedling length (cm) Control 50.00±10.00 11.26±1.39 9.63±0.18 20.89±1.57 43.33±8.81 12.06±0.97 9.01±1.05 21.07±2.02 25 ppm 80.00±11.54 5.83±1.45 9.03±1.94 14.86±3.39 70.00±11.59 9.20±0.62 6.36±1.63 15.56±2.25 50 ppm 76.67±3.34 8.46±0.55 6.56±1.61 15.02±2.16 63.33±14.52 8.76±0.59 7.10±0.64 15.86±1.23 75 ppm 76.67±6.63 5.80±1.51 5.26±0.84 11.06±2.35 60.00±8.81 6.56±0.78 4.33±1.14 10.89±1.92 100 ppm 66.67±14.52 6.03±0.91 3.90±1.50 9.93±2.41 53.33±20.27 5.00±1.40 3.23±0.39 8.23±1.79± ± Standard error Table 1. Eff ect of mercury on seed germination and growth of wheat varieties Blue Silver and Punjab 85Agric. conspec. sci. Vol. 71 (2006) No. 243Evaluation of Two Wheat Varieties for Phytotoxic Effect of Mercury on Seed Germination and Seedling Growthnot signifi cant. In var. Punjab 85, the highest reduc-tion in shoot length (5.0 cm) was recorded at 100 ppm of mercury, which was signifi cantly (P<0.05) diff erent compared to control (12.06 cm). Highest reduction in root length in wheat var. Blue Silver (3.90 cm) and var. Punjab 85 (3.23 cm) was found at 100 ppm of mercury which was signifi cantly (P<0.05) diff erent as compared to control. Both wheat varieties also showed signifi cant (P<0.05) reduction in seedling length at 75 and 100 ppm of mercury treatment as compared to other applications. Highest reduction in seedling length in var. Blue Silver (9.93 cm) and var. Punjab 85 (8.23 cm) was found at 100 ppm of mercury treatment.it enhanced the seed germination in both varieties compared to control. Th is means that mercury treat-ment could break the seed dormancy and enable seeds to germinate. Th e seedling growth on the other hand was reduced at all levels of mercury treatment in both varieties, which demonstrated that mercury reduces the seedling growth, particularly the root length. Th e root length of both wheat varieties was signifi cantly re-duced as compared to shoot length. Th is indicates that roots are sensitive parts of the plants and more damage occurred to roots as compared to the shoot since metal was absorbed through roots (Sattelmacher et al. 1993). Vizarova et. al. (1985) found negative eff ects of mercu-ry on young barley root growth as compared to above ground parts. Excessive mercury ions in soil also de-creased the chlorophyll contents of maize seedlings as shown by Vizarova et al. (1985).Kaslimuthu and Subramanian (1990) found reduc-tion in seed germination, seedling growth and protein contents of maize seedlings while Mukherjee and De (1996) reported the injurious eff ects in biochemical nature of tomato seedlings. Present study revealed that both varieties are sensitive to mercury as for seedling growth and root length. Varshney (1991) studied the phytotoxic eff ects of mercury on development of chlo-rophyll in cotyledons of two cucurbits and found that Luff a aegyptica was more sensitive to mercury treatment than Citrullus valgaris.Plants have evolved several mechanisms to pre-vent the toxic action of metals. Th ese include reduction of uptake into the root cells by changes in the kinetic properties of transporters and exudation of complex-ing agents into the rhizosphere (Watanabe and Osaki 2002). Once metals have entered the plant they induce the synthesis of the glutathione containing peptides phy-tochelatins and high cysteine containing proteins, the metallothioneins, which are able to bind the metal ions (Cobbet and Goldsbrough 2002, Hall 2002, Quartacci et al. 2000, Voskaoboinik et al. 2002). Ultimately the metals are stored in the vacuole in a relatively non-toxic form (Williams et al. 2000). Th ere have been a number Percentage tolerance Treatments T. aestivum var. Blue Silver T. aestivum var. Punjab 85 25 ppm 93.76 70.58 50 ppm 68.12 78.80 75 ppm 54.62 48.05 100 ppm 40.49 35.84  Triticum aestivum var. Blue Silver Triticum asetivum var. Punjab 85  Treatments Seed germination (%) Shoot length Root length Seedling length Seed germination (%) Shoot length Root length Seedling length 25 ppm 60.00+ 48.22 6.23 27.23 61.55+ 23.71 29.41 26.56 50 ppm 53.34+ 24.84 31.87 28.36 46.15+ 27.36 21.19 24.28 75 ppm 53.34+ 48.49 45.37 46.93 38.47+ 45.6 51.94 48.77 100 ppm 33.34+ 46.44 59.50 52.97 23.07+ 58.54 64.15 61.35 + = Percentage increase Table 3. Percentage tolerance of mercury by two wheat varietiesTable 2. Percentage reduction in seed germination and growth of wheat varieties Blue Silver and Punjab 85Th e results showed that the seed germination was enhanced while other variables such as shoot, root and seedling length showed reduction at all treatments of mercury in both varieties (Table 2). Th e highest reduction was observed at 100 ppm of mercury treatment. Th e tol-erance indices showed mercury toxicity of elevated levels of mercury in both wheat varieties (Table 3). Blue Silver was comparatively more tolerant than the var. Punjab 85 at most of levels of mercury treatment. At 100 ppm of mercury, var. Blue Silver showed 40.49% tolerance as compared to 35.84% in var. Punjab 85.DiscussionSeed germination of var. Blue Silver and var. Punjab 85 was not aff ected by elevated levels of mercury rather Agric. conspec. sci. Vol. 71 (2006) No. 244 Shagufta Naz JAMAL, M. Zafar IQBAL, Mohammad ATHARof attempts by diff erent laboratories to construct novel plants using genetic manipulation technologies that may have a greater tolerance to the presence of toxic metals (Belouchi et al. 1997, Macnair et al. 2000, Sasaki et al. 2004, Vitorello et al. 2005). Th ese plants are currently under intensive study to establish the mechanisms in-volved and for their possible use in pytoremediation (Faisal and Husnain 2004, Igwe and Abia 2006, Igwe et al. 2005).ReferencesAgricultural Statistics of Pakistan (-). Government of Pakistan. 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Evaluation of Two Wheat Varieties for Phytotoxic Effect of Mercury on Seed Germination and Seedling Growth

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