printed by Why should grain As levels be decreased? Food from plant or animal products contains both inorganic and organic As compounds in low levels. Of these forms, the organic As is considerably less toxic and readily expelled from the body through urine. The inorganic forms of As such as arsenate [As(V): H 2 AsO 4 1-, HAsO 4 2- ] and arsenite [As(III): H 3 AsO 3 °] are shown to be retained longer in the body and can be of potential concern (Johnson and Farmer et al.,1990; Cohen, et al., 2006). Arsenic has especially drawn attention in the South Asian countries already burdened with As toxicosis from polluted water. To minimize additional As exposure, rice cultivars having low As levels and favorable As speciation, i.e., high organic to inorganic ratios, in the rice grain, are required. Is yield and As concentration in rice grain related to high As levels in the soil? Rice is mostly grown in reduced flooded soils where As solubility and bioavailbility is higher than in oxidized soils. The plant physiological disorder called ‘straighthead’, which results in incomplete grain filling and decreased rice yields, is thought to be related to high As levels in flooded rice fields. For more than 10 years straighthead variability has been screened under continuous flooding following As application (to the soil) in the form of MSMA (mono-sodium- methyl-arsonate). It is not known if straighthead symptom is related to As concentration or As speciation in rice grain. This study is a collaborative effort of Dale Bumpers National Rice Research Center, Stuttgart, AR and Texas A&M University, College Station, TX to address the interest in developing rice cultivars with low rice grain As concentrations. Our objective was to screen a range of rice cultivars from the USDA world collection, with known and unknown tolerance to soil arsenic and compare their relative arsenic concentration and speciation in rice grain. We found wide cultivars specific differences in grain As levels and susceptibility to soil As toxicity when grown under uniform conditions. 1.Johnson, L. R., and Farmer, J. G. (1990) Use of human metabolic studies and urinary arsenic speciation in assessing arsenic exposure. Bulletin of Environmental Contamination and Toxicology. 43: Cohen, S., Arnold, L., Eldan, M., Lewis, A., Beck, B. (2006) Methylated Arsenicals: The implications of metabolism and carcinogenicity studies in rodents to human risk. Assessment Critical Reviews in Toxicology. 36(2): Yan, W. G., Dilday, R.H., Tai,T.H., Gibbons, J.W., McNew, R.W., and Rutger, J. N. (2005). Differential response of rice germplasm to straighthead induced by arsenic. Crop Science. 45: INTRODUCTION RESULTS & DISCUSSIONS Figure 2. Straighthead disorder symptom in rice panicle with incomplete grain filling and parrot beak formation. A total of thirty-seven rice cultivars of subspecies indica and japonica with known and unknown susceptibility to straighthead were selected for growth in a replicated trial in field at Stuttgart, AR. The two treatment soils included were a native soil known for high bioavailability of As and a conventional straighthead test plots amended with 6 lb/a MSMA before planting. The straighthead plots had a dimension of 6x4 feet with 6 rows (one feet apart). Straighthead scoring from 1-8 was assigned to rice cultivars based on the number of filled grains in the panicle as mentioned in Yan et al., Total arsenic concentration in milled rice grain was determined by ICP-MS following digestion by HNO 3 /H 2 O 2. Arsenic species were quantified from powdered grain by HPLC-ICP- MS following extraction with 1M TFA (Trifluoro-acetic-acid). METHOD Screening of rice cultivars for straighthead, grain Arsenic concentration and speciation Tushara Raghvan 1, Wen Gui Yan 2, Hesham A. Agrama 3, William D. James 4, Terry J. Gentry 5, and Richard H. Loeppert 5 1. Molecular and Environmental Plant Science, Texas A&M, 2890 Hwy 130 E., Stuttgart, AR 72160, 4. Elemental Analysis Laboratory, Texas A&M University, College Station, TX , 5. Soil & Crop Sciences, Texas A&M University, 370 Olsen Blvd, College Station, TX , USDA-ARS, 2. Dale Bumpers National Rice Research Center, 2890 Hwy 130 East, PO Box 1090, Stuttgart, AR 72160, 3. Rice Research and Extension Center, University of Arkansas University, 370 Olsen Blvd, College Station, TX BIBLIOGRAPHY CONCLUSIONS 1.Straighthead susceptibility is not related to As in the rice grain. 2.The selected rice grains accumulate excess As in the form of DMA possibly reducing the ill effects of net As consumption. 3.Screening rice cultivars for low inorganic As levels will be useful for populations consuming high inorganic As levels through water and food. Figure 6. Straighthead rating for 37 indica and japonica cultivars in MSMA-treated plots in 2004 (presented in increasing order). Figure 7. Grain arsenic levels in 37 indica and japonica cultivars from MSMA-treated and untreated plots in 2004 (presented in increasing order of straighthead rating). Figure 4. Soil As levels in conventional straighthead testing plots before and after MSMA treatment Figure 5. Rice cultivar Cocodrie in (a) straighthead testing plot with (b) typical sterile panicles induced by treating soil with 6.7 kg/ha MSMA applied before planting. (c) Cocodrie panicles with normal grain filling in soil with high bioavailable As and no MSMA treatment ABSTRACTRESULTS (continued) Rice cultivars covered the range of straighthead susceptibility from complete grain filling (rated 1) to panicles with no grain filling (rated 8).Rice cultivars covered the range of straighthead susceptibility from complete grain filling (rated 1) to panicles with no grain filling (rated 8). In this sample set many indica cultivars were tolerant to straighthead compared to the japonica cultivarsIn this sample set many indica cultivars were tolerant to straighthead compared to the japonica cultivars Increased susceptibility to straighthead could result in probable increased yield loss under unfavorable conditions.Increased susceptibility to straighthead could result in probable increased yield loss under unfavorable conditions. Figure 3. Straighthead rating assigned to plants grown in MSMA treated plot as given in Yan et al., (2005). Straighthead susceptibility is not related to grain As levels.Straighthead susceptibility is not related to grain As levels. Some cultivars with low grain As levels from native soil had high levels in MSMA treatment and vice versa, indicating that certain soil As species in may be preferably taken up by some cultivars.Some cultivars with low grain As levels from native soil had high levels in MSMA treatment and vice versa, indicating that certain soil As species in may be preferably taken up by some cultivars. Figure 8. Grain As species in five cultivars from MSMA treated and non-treated soil. The inorganic As levels in grain are detectable as As(III) in the TFA extractions.The inorganic As levels in grain are detectable as As(III) in the TFA extractions. No MMA was found in the grain during speciation analysis.No MMA was found in the grain during speciation analysis. The As(III) levels in the grains from MSMA treated and non-treated plots were the sameThe As(III) levels in the grains from MSMA treated and non-treated plots were the same The increased As uptake from MSMA treatment resulted in significant increase DMA.The increased As uptake from MSMA treatment resulted in significant increase DMA. Figure 1. Arsenic species found in rice 1= no floral sterility 2= 1 to 20 % floral sterility 3= 21 to 40% floral sterility 4= 41 to 60% floral sterility 5= 61 to 80% floral sterility 6=81 to 100% floral sterility 7=panicles emerged from boot but 100% floret sterility 8=panicles partially emerged from the boot and 100% floral sterility 9=panicles not emerged from the boot