Uptake and translocation of selenium-75 in Zea mays

A series of water culture experiments with Zea mays was carried out to examine the nature of plant uptake and translocation of selenite and selenate using 75Se. From the results it is concluded that selenium is taken up immediately and translocated to the plant tops. In the exuded xylem sap 80-90% of the 75Se was recovered in the amino acid fraction when the selenium was present in the nutrient solution as selenite. When selenate was added, about 90% was recovered in the xylem sap as selenate. Varying the nitrogen level showed that a high N-level strongly increased the selenium concentration in the roots exposed to selenite, mainly by an increase in the selenite fraction. The nitrogen decreased the translocation of the selenium, causing a lower concentration in the tops of the plants, but a relative increase in the amino acid selenium. When the plants were grown at a low level of sulphur with selenite in the nutrient solution, the concentration of selenium in roots and leaves was roughly doubled even when the yield of dry matter was unchanged. The selenium concentration in the xylem sap was 7-8 times higher at the low sulphur level than at the high level. The relative distribution between the selenium fractions was affected by the sulphur level. (author)