) showed that increasing SO 4 2– concentrations in the soil solution not only influenced S concentrations in Brassica , but also enhanced glucosinolate content. However, when Brassica plants were exposed to different sodium selenate concentrations
Pai-Tsang Chang, Marc W. van Iersel, William M. Randle, and Carl E. Sams
Dean A. Kopsell, Carl E. Sams, T. Casey Barickman, Dennis E. Deyton, and David E. Kopsell
investigate tolerances to different Se forms and concentrations. Therefore, the objectives of this study were to evaluate the potential to fortify basil and cilantro shoot tissues through foliar application of both selenate-Se and selenite-Se at different Se
Dean A. Kopsell and William M. Randle
Selenium and sulfur have similar chemical structures. This allows Se to be absorbed and incorporated in the same assimilation pathways as S. Onions (Allium cepa L.) are a crop with unique S metabolism, responsible for growth and flavor intensity. Because of the antagonistic behavior of the two ions, the effects of Se on S and Se nutrient depletion and tissue accumulation were investigated. `Granex 33' onions were grown in nutrient solutions with one concentration of S and increasing Se concentrations. Selenium was applied as sodium selenate (Na2SeO4) at concentrations of 0, 0.5, 1.0, 1.5, and 2.0 mg·L-1. Selenium depletion from the nutrient solution increased linearly with increasing Na2SeO4 treatment concentrations. Sulfur depletion increased and then decreased with increasing Na2SeO4 treatment concentrations. Selenium and S accumulation were highest in leaf tissues, less in root tissues, and lowest in bulb tissues at plant maturity. Selenium accumulation increased linearly with increasing Na2SeO4 for all tissues analyzed. Sulfur accumulation in leaf and bulb tissues was quadratic in response to increasing SeO4 -2, while S in root tissues decreased linearly with increasing Na2SeO4. Low concentrations of Na2SeO4 in our study enhanced S uptake and accumulation. Previously, Se was thought to competitively inhibit S uptake and metabolism.
Dean A. Kopsell, William M. Randle, and Harry A. Mills
Brassica species are important economic vegetable crop, and it is possible to enrich them with selenium (Se) to supplement human diets. The health benefits associated with increased Se consumption include cancer suppression, reduced heart disease, and immune system enhancement. Vegetables enriched with Se can serve as excellent delivery systems of organic Se forms, which are more beneficial than traditional Se supplements. The vegetable Brassicas are consumed not only for their flavor, but also for their nutritional content. A heterogeneous population of rapid-cycling B. oleracea was used as a model system to study the effects of added selenate-Se on other plant micro- and macronutrients. Plants were grown in nutrient solutions amended with sodium selenate at 0.0, 3.0, 6.0, and 9.0 mg·L–1. Leaf tissues were then analyzed for nutrient content. Boron (P = 0.001) and iron (P = 0.01) content decreased, while selenium (P = 0.001), sulfur (P = 0.001), and potassium (P = 0.001) increased with increasing selenate-Se. Significant quadratic responses were found for calcium (P = 0.02), copper (P = 0.05), magnesium (P = 0.01), and molybdenum (P = 0.01). No differences in leaf fresh or dry weight were detected. Changes in plant nutrient content can be expected when Brassicas are enhanced for delivery of beneficial organic Se.
Dean A. Kopsell and William M. Randle
Beneficial effects of selenium (Se) can be delivered to humans through enriched plant foods. Plants in the Brassicaceae are good sources of sulfur (S) and can be enriched with Se. Breeding plants to be more efficient at Se accumulation may complement enrichment efforts. Because Se and S are chemically similar and can compete in plant metabolic pathways, S levels must be considered when attempting to manipulate Se, and vice versa. The objectives of this study were to establish genetic variances for S and Se accumulation, and to determine if simple recurrent selection could be used to manipulate Se accumulation in a rapid-cycling (Brassica oleracea L.) population. Progeny from a North Carolina Design II mating scheme were grown in two seleniferous environments and expressed variability for Se and S accumulation. Narrow sense heritability estimates for Se and S accumulation were moderate (0.55 to 0.75), which suggested progress was possible. However, standard errors were large and may influence expected progress during improvement efforts. Plants of a rapid-cycling B. oleracea were also subjected to two cycles of divergent selection for Se accumulation in leaf tissues. Realized heritabilities were high during selection for both high and low Se accumulation. Simultaneous evaluation of all populations revealed actual gains from selection to be 4.8% and 4.0% per selection cycle for high and low Se accumulation, respectively. Predicted gains for Se accumulation in the plants were 6.8%. Selection for Se accumulation was successful and indicates population improvements for such traits are possible within the B. oleracea analyzed. Breeding plants that are more efficient at accumulating Se could be a useful tool towards Se enrichment.
Dean A. Kopsell and William M. Randle
Four cultivars of onion (Allium cepa L. `Primavera', `Granex 33', `Pegasus', and `Sweet Success') were grown to maturity in modified nutrient solutions with or without 2.0 mg·L-1 Na2 SeO4 (1.51 mg·L-1 SeO4 -2). Selenium did not affect total flavor precursor content (ACSO) in `Granex 33', `Pegasus', and `Sweet Success'. However, Se affected several individual ACSOs and precursor intermediates. Selenium decreased γ-L-glutamyl-S-(1-propenyl)-L-cysteine sulfoxide and trans(+)-S-(1-propenyl)-L-cysteine sulfoxide content in all four cultivars. (+)-S-Methyl-L-cysteine sulfoxide content was higher while (+)-S-propyl-L-cysteine sulfoxide content was lower with the added Se for two cultivars. Selenium lowered total bulb S content in all cultivars, and increased the percentage of total S accumulated as SO4 -2 in three cultivars. The effect of Se on the flavor pathway was similar to that found when onions were grown under low S-concentrations. Flavor changes can be expected when onions are grown in a high Se environment, however, specific changes may be cultivar dependent.
Sara Arscott and Irwin Goldman
demonstrate that broccoli sprout growth may be significantly reduced at levels of 635 μM Se but not 127 μM Se as sodium selenate. Fig. 2. Trial 2: Gain in biomass (GIB) of broccoli, mung bean, and onion sprouts for 2 harvest days. Bars, from left to right
Heather D. Toler, Craig S. Charron, Carl E. Sams, and William R. Randle
substitutes for S in physiological and metabolic processes ( Anderson and Scarf, 1983 ). Charron et al. (2001) , for example, found that total glucosinolate production in rapid-cycling B. oleracea decreased when grown in the presence of sodium selenate
Dean A. Kopsell and William R. Randle
The affects of selenium (Se) on sulfur (S) uptake and metabolism were evaluated in `Granex 33' onions. Plants were grown in a half-strength Hoagland's solution and modified with increasing Se fertility. Selenium was added as sodium selenate. During growth, plants were sampled biweekly and divided into root, bulb, and foliar tissue. Tissues were dried and ground for total S, and wet-ashed for total Se (GFAA). Selenium increased S uptake by onions. As Se increased in concentration, S utilization first increased then decreased in a quadratic trend.
Menahem Edelstein, Daniel Berstein, Moshe Shenker, Hasan Azaizeh, and Meni Ben-Hur
role in recycling and delivering Se from the soil into the food chain, even though Se has not been yet confirmed as an essential plant micronutrient. In Finland, for example, selenate has been added to fertilizers since 1984 to increase the Se in soils