Uptake and distribution of iodine in grass and clover plants grown in solution culture.

Perennial ryegrass (S23), timothy (S48), white clover (S100) and red clover (Hungaropoly), grown in culture solutions containing 0.2 x 5.0 x M-potassium iodide, showed relatively small differences in iodine uptake. The lowest uptake occurred with timothy, the species that also produced the lowest yields of dry matter. Red clover had the lowest concentration of iodine in the shoots on all treatments, its difference from the other species being proportionately greater at the higher levels of iodide supply. The transport of iodine from roots to shoots was restricted in all species, with roots having much greater concentrations of iodine than shoots. However, with the exception of red clover, transport to the shoots increased considerably as the supply of iodide was increased. Two diploid and two tetraploid varieties of red clover also showed only small differences in uptake and concentration of iodine in their shoots and roots, although the tetraploid varieties did have somewhat lower concentrations in their shoots at the lowest level of iodide supply. Plants of perennial ryegrass and red clover grown for eight weeks on solutions containing 1.0 x M-iodide had higher concentrations of iodine in dead and senescent leaves than in green shoot material. Iodide was taken up much more readily than iodate, and chloride, even at concentrations up to 50 000 times the iodide concentration, did not depress the uptake of iodide. 1.0 x and 1 .O x