Radicular and foliar uptake, and xylem- and phloem-mediated transport of selenium in maize (Zea mays L.): a comparison of five Se exogenous species

Background Various species of selenium (Se) can be radicularly or foliarly absorbed by plants. However, differences of these species in uptake and transport via the xylem or phloem remain unclear. Methods Maize (Zea mays L.) seedlings were grown in hydroponic solutions with five exogenous Se species [inorganic forms: selenite and selenate; and organic forms: selenomethionine (SeMet), methyl-selenocysteine (MeSeCys), and selenocystine (SeCys(2))] radicularly or foliarly applied on the plants. Results Under radicular application, the seedlings showed higher root uptake of organic Se than inorganic forms. Moreover, the largest proportion of Se in the shoots was found under MeSeCys treatment. Se accumulation under foliar application was low. The uptake of inorganic Se was higher than that of organic forms under foliar treatments. The phloem of maize showed a strong ability for downward Se transport, although the proportion of that in the whole plant was small (<10%). The largest percentage of Se distributed in the roots was found under MeSeCys treatments. Conclusions As a C-4 species, maize can accumulate much Se from organic Se through root uptake but from inorganic forms through leaf uptake. It can transport much Se from the source to the sink with the application of organic Se, especially MeSeCys.