Selenium and sulfur influences glucosinolate metabolism in hydroponically grown rapid cycling Brassica oleracea

Glucosinolates are sulfur-containing secondary plant metabolites commonly found in plants in the family Brassicaceae. The presence of selenium in soils can result in an accumulation of selenoamino acids, an increase in the uptake of sulfur, and an inhibition in the production of glucosinolates in Brassica species. This study was undertaken to determine the extent of selenium\u27s impact on selenoamino acid accumulation, sulfur uptake, and glucosinolate production in Brassica oleracea. Rapid cycling B. oleracea plants were grown hydroponically in half strength Hoagland\u27s nutrient solution with selenium treatments delivered as sodium selenate in concentrations of 0.0, 0.5, 0.75, 1.0, and 1.5 ppm. Elevated sulfur treatments of 37 ppm sulfate and 37 ppm sulfate/ 0.75 ppm selenate were incorporated to compare with selenium treatments. Plants were harvested and freeze-dried one to two days prior to anthesis. Selenium and sulfur content of plant tissue was determined by flame atomic absorption spectrophotometry and a Leco 232 S-determinator. Glucosinolate content of leaf tissue was determined by high performance liquid chromatography (HPLC). Selenium concentration in the nutrient solution was positively correlated with selenium and sulfur uptake in the plants. The sulfur concentration of plants exposed to selenium was equal to or greater than the sulfur concentration of plants exposed to elevated sulfur in the nutrient solution. In spite of higher sulfur concentrations, there was a statistically significant decrease in production of 5 of the 7 glucosinolates analyzed in selenium enriched plants. Plants in elevated sulfur treatments had higher glucosinolate production than selenium treated plants. These results suggest that selenium either up-regulates or prevents the down-regulation of sulfur uptake in B. oleracea. In addition, selenium\u27s presence within the plant seems to have a negative impact on the production of certain glucosinolates despite adequate availability of sulfur

Mycorrhizal Stimulation of Leaf Gas Exchange in Relation to Root Colonization, Shoot Size, Leaf Phosphorus and Nitrogen: A Quantitative Analysis of the Literature Using Meta-Regression

Arbuscular mycorrhizal (AM) symbiosis often stimulates gas exchange rates of the host plant. This may relate to mycorrhizal effects on host nutrition and growth rate, or the influence may occur independently of these. Using meta-regression, we tested the strength of the relationship between AM-induced increases in gas exchange, and AM size and leaf mineral effects across the literature. With only a few exceptions, AM stimulation of carbon exchange rate (CER), stomatal conductance (gs) and transpiration rate (E) has been significantly associated with mycorrhizal stimulation of shoot dry weight, leaf phosphorus, leaf nitrogen: phosphorus ratio and percent root colonization. The sizeable mycorrhizal stimulation of CER, by 49% over all studies, has been about twice as large as the mycorrhizal stimulation of gs and E (28% and 26%, respectively). Carbon exchange rate has been over twice as sensitive as gs and four times as sensitive as E to mycorrhizal colonization rates. The AM-induced stimulation of CER increased by 19% with each AM-induced doubling of shoot size; the AM effect was about half as large for gs and E. The ratio of leaf N to leaf P has been more closely associated with mycorrhizal influence on leaf gas exchange than leaf P alone. The mycorrhizal influence on CER has declined markedly over the 35 years of published investigations

Bumble Bee on Echinacea

Bumble bee on an Echinacea bloom. Taken last year at Beardsley Farm in Knoxville during an OSCP tomato production workshop.https://trace.tennessee.edu/utiaphoto_2013/1010/thumbnail.jp

Sunflower Preparing to Bloom

Sunflower getting ready to bloom at the Organic Crops Unit Spring/Summer 2012.https://trace.tennessee.edu/utiaphoto_2013/1115/thumbnail.jp

Tomato Grafting Demonstration

Institute employee John Cummins showing OSCP tomato workshop participants how to graft tomatoes June 11, 2012.https://trace.tennessee.edu/utiaphoto_2013/1045/thumbnail.jp

Zinneas at the UT Farmers Market

Flowers for sale by a vendor at the UT Farmer\u27s Market July 25, 2012.https://trace.tennessee.edu/utiaphoto_2013/1035/thumbnail.jp

Chef John Antun at a Cooking Demonstration at the UT Farmers Market

The late and beloved chef John Antun giving a cooking demonstration at the UT Farmer\u27s Market in 2010.https://trace.tennessee.edu/utiaphoto_2013/1015/thumbnail.jp

Organic and Sustainable Crop Production Moveable High Tunnel Workshop

Taken at an OSCP Moveable High Tunnel workshop in 2012 at Bountiful Blessing Farm in Middle Tennesseehttps://trace.tennessee.edu/utiaphoto_2013/1078/thumbnail.jp

Grapes at Organic and Sustainable Crop Production Grape Workshop

Unripened bunch of grapes at a OSCP Grape Production workshop in 2012.https://trace.tennessee.edu/utiaphoto_2013/1103/thumbnail.jp

Sunflower Almost Blooming

Sunflower almost blooming OSCP insect management workshop June 2011.https://trace.tennessee.edu/utiaphoto_2013/1114/thumbnail.jp