Selenium Tissue Analysis Values of Various Plant Species

Selenium is unevenly distributed within plant tissues. Actively growing tissues usually contain the highest amounts of Se (35), and many plant species accumulate higher amounts of selenium in shoot or leaf tissues than in root tissues. Plant species differ greatly in their ability to accumulate seed selenium. Nelson and Johnson (123) reported seed selenium levels up to 3750 µg Se g^-1 dry weight in native milkvetch (Astragalus L.) species. Selenium accumulation in a rapid-cycling Brassica oleracea L. population increased linearly with increasing Na₂SeO₄ treatment concentrations in nutrient solution culture, ranging from nondetectable at 0 mg Na₂SeO₄ L^-1 to 753 µg Se g^-1 dry weight at 7.0 mg Na₂SeO₄ L^-1 (124). Selenium is also unevenly distributed within seeds. In dried grains of barley, the husk and pericarp accumulated selenium up to 0.6 µg Se g^-1, the scutellum 0.4 µg Se g^-1, the embryo 0.3 µg Se g^-1, and the aleurone layer, embryonic leaves, and root initials 0.2 µg Se g^-1 (125).

Selenium treatment and selenium-enriched media will affect seed germination in a number of species. Soybeans (Glycine max Merr.) pretreated with 10 to 100 g Se ha^-1 as either seed or foliar treatments were grown on a nonseleniferous sandy loam soil and subsequently produced seeds accumulating 0.78 to 38.5 mg Se kg^-1. When these seeds were planted without application of selenium fertilizer, the concentration of harvested seeds decreased to 0.11 to 1.02 mg Se kg^-1 (126). Seed germination was reduced if wheat (Triticum aestivum L.) was grown in soils with >16.0mg Se kg^-1 (127). Weight of fresh Alfalfa seedling was suppressed in response to >10.0 mg Se L^-1 in solution culture (128). Turnip (Brassica campestris L.) seed germination was >98% when seeds were incubated in <484 mg NaSeO₃ L^-1, but decreased to 51% if the concentration of NaSeO₄ was increased to 4.84 g NaSeO₃ L^-1. In response to NaSeO₃, turnip seed germination was 97% at Se levels <95 mg NaSeO₃ L^-1, 53% at 484 mg NaSeO₃ L^-1, 17% at 951 mg NaSeO₃ L^-1, and 0% at 4.84 g NaSeO₃ L^-1 (129). Interestingly, several studies report that seed germination was enhanced in response to <1.0 mg Se L^-1 in nutrient solutions (127,130,131). Activity of �-galactosidase, an enzyme important in the hydrolysis of complex carbohydrates during seed germination, in fenugreek (Trigonella foenum-graecum L.) was enhanced by 40% when exposed to 0.5mg L^-1 Na₂SeO₃-seed treatment, but decreased by 60 to 65% if Na₂SeO₃-seed treatment was increased to 1 mg L^-1 (132). Seed germination was >96% after 72 h in a rapid-cycling Brassica oleracea population when the content of selenium in the seed was <700 µg Se g^-1 dry weight (124).