Rate-Limiting Steps in Selenium Assimilation and Volatilization by Indian Mustard1

Abstract

Se can be accumulated by plants and volatilized to dimethylselenide, providing an attractive technology for Se phytoremediation. To determine the rate-limiting steps in Se volatilization from selenate and selenite, time-and concentration-dependent kinetics of Se accumulation and volatilization were studied in Indian mustard (Brassica juncea). Time-dependent kinetic studies showed that selenate was taken up 2-fold faster than selenite. Selenate was rapidly translocated to the shoot, away from the root, the site of volatilization, whereas only approximately 10% of the selenite was translocated. For both selenate-and selenite-supplied plants, Se accumulation and volatilization increased linearly with external Se concentration up to 20 M; volatilization rates were also linearly correlated with root Se concentrations. Se-volatilization rates were 2-to 3-fold higher from plants supplied with selenite compared with selenate. Se speciation by x-ray absorption spectroscopy revealed that selenite-supplied plants accumulated organic Se, most likely selenomethionine, whereas selenate-supplied plants accumulated selenate. Our data suggest that Se volatilization from selenate is limited by the rate of selenate reduction, as well as by the availability of Se in roots, as influenced by uptake and translocation. Se volatilization from selenite may be limited by selenite uptake and by the conversion of selenomethionine to dimethylselenide.

Se(IV), Se(VI), Cu and Zn phytotoxicity in correlation to their accumulation in <i>Sinapis alba</i> L. seedlings

“…However, this statement was during our experiments with S. alba fully confirmed for selenite, discrepancy was observed for selenate when transformation index (Ti) for tested concentrations did not exceed value 0.39 (Table 3). Results for selenate are in agreement with those of de Souza et al (1998). These authors determined through Se timedepending kinetic that only 10% of selenates absorbed by Indian mustard (Brassica juncea) moved from the roots into the shoots.…”

“…Selenium lower toxicity in seedlings shoots can be explained by transformation of inorganic selenium to organic compounds that are transported from the roots to the shoots , Kahakachchi et al 2004). Many authors (de Souza et al 1998, Kahakachchi et al 2004, Zayed et al 1998 www.plantroot.org 18 2009) introduced very weak selenite translocation from the roots to the shoots and this statement also confirmed here introduced results (Table 3). By this low translocation and Se storage in the roots can also explain many times higher IC 50 values for shoots than those for roots growth reduction.…”

Selenium Volatiles as Proxy to the Metabolic Pathways of Selenium in Genetically Modified Brassica juncea

“…Approximately 10 times more DMeSe and DMeDSe (normalized to sample weight) is produced in all plant types when the plants were supplemented with selenite than with selenate (8).…”

Sodium selenite treatment of vegetable seeds and seedlings and the effect on antioxidant status

“…In contrast, the absorption of selenite occurs in a different way (Terry et al, 2000), through a phosphate transporter (Zhao et al, 2010). Once absorbed, selenite remains in organic form (De Souza et al, 1998;Cartes et al, 2006) and has been shown to be a more efficient inducer of glutathione peroxidase (Cartes et al, 2005). Selenium is thought to be associated with antioxidant metabolism (Lin et al, 2012;Feng et al, 2013) through its function as a cofactor of selenoenzymes (Combs, 2001); its deficiency could provoke changes in the cellular redox balance.…”

“…Selenate is absorbed through a transport process coupled to a H + -ATPase, with the help of a sulfate (Terry et al, 2000) or silicon transporter (Zhao et al, 2010); once absorbed by the plants, maintains the inorganic form (De Souza et al, 1998;Cartes et al, 2006). In contrast, the absorption of selenite occurs in a different way (Terry et al, 2000), through a phosphate transporter (Zhao et al, 2010).…”