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- Author or Editor: William R. Randle x
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.
A real-time polymerase chain reaction (PCR) assay has been developed for the detection and quantification of Botrytis aclada (Fresenius), a causal agent of neck rot in onion (Allium cepa L.) bulbs. The assay uses TaqMan probe-based chemistry to detect an amplicon from the L45-550 region of B. aclada while using a DNA sequence from the onion serine acetyl transferase gene (SAT1) as a control. The assay detection limits for B. aclada and onion were 10 pg·μL−1 of genomic DNA. The detection limit for lyophilized B. aclada mycelium was 1 μg. The presence of onion tissue in the samples did not affect the performance of the real-time PCR assay. The assay distinguished among different amounts of B. aclada mycelium growing on onion disks that were inoculated with 0, 102, or 104 B. aclada conidia. Visual observations during the incubation period corresponded with changes in real-time PCR results. This assay could be used to determine the amount of B. aclada mycelium in bulbs during growth, harvest, and storage, thus giving researchers an objective and efficient tool by which to quantify the growth rate and virulence of B. aclada strains in vivo.
Glucosinolates are sulfur-containing secondary plant metabolites commonly found in the family Brassicaceae. The presence of selenium in soils increases the uptake of sulfur and inhibits the production of glucosinolates in brassicaceous plants. This study was undertaken to determine the extent of selenium's impact on sulfur uptake and glucosinolate production in Brassica oleracea L. Rapid-cycling B. oleracea plants were grown hydroponically in half-strength Hoagland's nutrient solution with selenium treatments delivered as sodium selenate concentrations of 0.0, 0.5, 0.75, 1.0, and 1.5 mg·L−1. Elevated sulfur treatments of 37 mg·L−1 sulfate and 37 mg·L−1 sulfate/0.75 mg·L−1 selenate were incorporated to compare with selenium treatments. Plants were harvested and freeze-dried 1 day before anthesis. Selenium and sulfur content of plant tissue was determined by flame atomic absorption spectrophotometry and a carbon–nitrogen–sulfur analyzer. Glucosinolate content of leaf tissue was determined by high-performance liquid chromatography. Selenium and sulfur uptake in plants positively correlated with selenium concentration in the nutrient solution. The sulfur concentration of plants exposed to selenium equaled or exceeded the sulfur concentration of plants exposed to elevated sulfur. Despite higher sulfur concentrations, there occurred a statistically significant decrease in production of five of the seven glucosinolates analyzed in selenium-enriched plants. Plants that underwent elevated sulfur treatments had higher glucosinolate production than selenium-treated plants. These results suggest that selenium either upregulates or prevents the downregulation of sulfur uptake in B. oleracea. In addition, the presence of selenium within the plant appears to have a negative impact on the production of certain glucosinolates despite adequate availability of sulfur.