Transport of Selenate and Selenite into Astragalus Roots

Abstract

Abstract. After giveln an accumiiulation ratio greater thani one, but evidence for an active transport of this ionl is unclear because of siome apparent non-biological uptake (15). Since selenate and selenite are both assimilable ions (1,9,10,11,12,16,17), accunmulationi of selenium by these roots could be either ani accumulation of the ions against an electrochemical gradient or an accumulation of seleno-metabolites whose synthesis is energy dependent. The data presented here will show that selenate can accumulate largely unchanged in excised roots of 2 species of Astragaluts; much of the selenite however, is changed into other selenium comll)ounds or possibly adsorbed. Materials and MethodsPreparationi a(id Growth of Seedlings. Techni(quies described earlier for the preparation and growth of seedlings (15) were used in these 'experiments but moldified as follows: after germination in the dark for 2 days, (21-22°), the seedlings were laterally illunminated before a bank of fluorescent lights at an intensity of 4300 ft-c for 3 more days (22-25°).This research w-as supported by Public Health Research Grant GM 09086 from the National Institutes of Healtlh.ion Absorption Procedure. The preparation of root tips and the conditions for the uptake of selenate and selenite were identical with the procedures de-scribed earlier (15).Fractionation of Radioactive Tissues. At the end of thle uptake period, roots were blotted on filter paper and weighed rapidly. For nleasurement of the total radioactivity abs,orbed, roots were prepared as described earlier (15). For measurement of the ethanol insoluble fraction, the weighed roots were suiccessively extracted with 70 % (v/v) ethanol 6 to 8 times until the radioactivity in the ethanol extract was approximately 1 % of the radioactivity in the first extraction. The acid digestion mixture was slowly added to the extracted roots to avoid foaming, and the extracted roots were digested as described earlier (15). A precipitate which formed in the digest of the ethanol-extracted roots had no effect on the counts. Samples for total and ethanol-insoluble radioactivity were run in triplicate.For biochemical analysis of soluble radioactive components, weighed roots from 24 colanders were pooled and extracted with 48 ml of 70 % ethanol.Column Chromatography. The use of Dowex-1-Cl coltumns for identification of selenite and selenate has been described previously ( 12).Paper Chromatographiy. XVhatman No. 1 was used throughout. The following solvent systems were used: No.

Physiological characteristics of selenite uptake by maize roots in response to different pH levels

“…Selenite uptake was reported to be inhibited by only 35% and 20% after addition of a respiratory inhibitor (hydroxylamine) to the nutrient solution and was considered a passive process (Arvy, 1989(Arvy, , 1993. However, other researchers showed that low temperature and respiratory inhibitors inhibited selenite uptake by more than 80% and 70% at pH 4.0 (Ulrich and Shrift, 1968;Shrift and Ulrich, 1969). The discrepancy in results may be related to the effect of pH on selenite species in the absorption solution.…”

“…Previous research has suggested that selenite is accumulated through passive diffusion processes (Shrift and Ulrich, 1969). At low pH, the high selenite uptake observed (Fig.…”

“…The mechanisms of selenate uptake in plants have been extensively studied, and selenate is absorbed by roots through cell membranes by sulfate transporters (Brown and Shrift, 1982). The mechanisms of selenite uptake by roots remain unclear (Shrift and Ulrich, 1969;Arvy, 1989Arvy, , 1993. Selenite uptake was reported to be inhibited by only 35% and 20% after addition of a respiratory inhibitor (hydroxylamine) to the nutrient solution and was considered a passive process (Arvy, 1989(Arvy, , 1993.…”

In Situ Speciation and Distribution of Toxic Selenium in Hydrated Roots of Cowpea

“…By contrast, little is known about the uptake mechanism involved in Se [IV] in plant roots. Some studies suggested that Se [IV] is taken up via passive diffusion (Shrift and Ulrich, 1969;Arvy, 1993). Recently, Zhao et al (2010) reported that the uptake of Se [IV] is mediated by the silicon (Si) influx transporter Lsi1 (OsNIP2;1) in rice (Oryza sativa).…”

Variation in [75Se]selenate uptake and partitioning among tomato cultivars and wild species

“…Organic Se, selenate and selenite have all been drainage water (Grattan et aL, 1987). shown to be taken up by a number of plants Previous studies investigating selenate/sulphate (Hamilton & Beath, 1963 a, b), with selenate being interactions have generally used very high levels of more readily taken up than selenite by a number of selenate (25-100/*M, or approximately 150-species (Schrift & Ulrich, 1969;Asher, Butler & 8000/*g T^) and low levels of sulphate (in the range Peterson, 1977). Selenite is readily adsorbed or fixed 10-100 /*M), relative to those typically found in soils, by clay particles and iron oxides (Hamdy & Gissel-particularly high sulphate/saline soils.…”