Selenium Absorption by Two-Grooved Milkvetch and Western Wheatgrass from Selenomethionine, Selenocystine, and Selenite

Abstract

Selenium (Se) occurs in various forms in soils, including inorganic selenite and selenate and organic selenomethionine. Plant uptake of the inorganic, but not the organic forms, has been studied extensively. Organic-Se uptake was therefore examined in two-grooved milkvetch (Astragalus bisulcatus (Hook.) Gray), a Se-accumulating forb, and western wheatgrass (Pascopyrum (Rydb.) Love), a non-Se accumulating grass. Plants were grown for 56 days in nutrient culture enriched with 1 or 2 mg Se literl as sodium selenite or 0.3 or 0.6 mg Se liter-1 as Se-DLmethionine or Se-DL-cystine. Growth was not affected by the Se treatments. Selenium concentrations in shoots were proportional to nutrient-solution concentrations for both species grown in sodium selenite and selenocystine, and for wheatgrass when grown in selenomethionine. Selenium concentrations in milkvetch were not increased by the higher concentration of selenomethionine. Shoots of milkvetch, growing in the low-Se treatment contained 243, 283, and 47 mg Se g-1, for the sodium selenite, selenomethionine, and selenocystine treatments, respectively, whereas values for the wheatgrass were 20, 32, and 17. Shoot:root Se concentrations were 1.2, 0.7, and 0.4 in milkvetch and 0.1, 0.5, and 0.1 in wheatgrass for the sodium selenite, selenomethionine, and selenocystine, respectively. Selenium is more readily transported to shoots in the accumulator plant, or conversely; there is a barrier to Se movement to shoots in the nonaccumulator plant. Wheatgrass contained sufficient Se to be of concern in animal toxicosis and because of greater dry matter yield accumulated as much or more Se than did the milkvetch.

Absorption of Excess Selenium and Sulfur by Plants and Animals

“…Selenomethionine is two to four times more available to plants than selenite (Williams and Mayland 1992) and its uptake is under metabolic control (Abrams et al 1990b). Selenocystine is less bioavailable than selenomethionine (Williams and Mayland, 1992). In some soils, nearly 50% of the Se may be in organic forms (Abrams et al, 1990b).…”

“…These methylated fonns are likely absorbed by plants. The Se enrichment of plants growing in Se-free nutrient culture could have occurred by foliar absorption of Se volatilized from udj acent plants growing in selenized nutrient culture (Williams and Mayland 1992).…”

Selenium speciation and bioavailability in Dutch agricultural soils: the role of soil organic matter

“…In soil solution, Se is present as selenate and selenite anions as well as organic Se (Tolu et al, 2011;Stroud et al, 2012). Soluble selenate and selenite are the major bioavailable chemical forms for plants, although some research showed that selenoamino acids such as selenomethionine and selenocystine can also be taken up (Abrams et al, 1990b;Williams and Mayland, 1992;Kikkert and Berkelaar, 2013). For the anionic selenate and selenite, adsorption to metal (hydr)oxides and to the edges of clay minerals is the major mechanism that controls their solid solution distribution Vuori et al, 1989).…”

“…Inorganic selenate can be taken up directly by roots and easily translocated to the shoots, whereas selenite tends to be accumulated in root tissue (Zayed et al, 1998;Hopper and Parker, 1999;Li et al, 2008;Kikkert and Berkelaar, 2013). Previous studies have shown that some small organic Se molecules, such as selenomethionine and selenocystine, can also be taken up by plants (Abrams et al, 1990b;Williams and Mayland, 1992;Kikkert and Berkelaar, 2013), and selenomethionine is more readily taken up by roots and quickly transported to the shoots than selenocystine (Kikkert and Berkelaar, 2013). However, Supriatin et al (2015a) showed that most of soluble Se in Dutch agricultural soils consists of colloidal-sized organic Se, whereas inorganic selenite or selenate and small organic Se molecules were hardly measurable.…”

“…Among these inorganic and organic Se forms, the soluble inorganic selenate and selenite and soluble organic Se, such as selenomethionine and selenocystine, can be taken up directly by plants (Abrams et al, 1990b;Williams and Mayland, 1992;Zayed et al, 1998;Hopper and Parker, 1999;Li et al, 2008;Kikkert and Berkelaar, 2013). Our previous study has shown that agricultural soils in the Netherlands contain mostly low amounts of Se (0.12 to 1.97 mg kg -1 , with an average of 0.58 mg kg -1 ), with most of Se in organic form and only a small fraction of inorganic selenite (Supriatin et al, 2015b).…”