CHANGES IN RADIOCESIUM UPTAKE AND DISTRIBUTION IN WHEAT DURING PLANT DEVELOPMENT - A SOLUTION CULTURE STUDY

Spring wheat plants were grown in a Cs-137 labelled nutrient solution, either in the presence or absence of NH4 as a secondary N source. Bet ween 11 and 64 days after sowing (DAS), plants were harvested on nine occasions. The plants supplied with NH4 and NO3 had lower root Cs-137 Activity Concentrations (AC) than those supplied with NO3 only. Shoot AC were equal in both nutrition treatments. Shoot and root Cs-137 AC ( dry weight basis) showed the same trends with plant age in both nutrit ion treatments. Shoot AC almost doubled between 11 and 28 DAS after wh ich they gradually decreased concomitant with a similar decrease in K concentrations. Root AC were always higher than shoot AC and increased to a maximum at 35 DAS after which they fluctuated. Expressed on a ti ssue water basis, the Cs-137 AC varied less during plant age than did dry weight based AC. Furthermore, root and shoot AC expressed on a tis sue water basis were almost equal. It is shown that the initial increa se in Cs-137 AC in, both root and shoot can largely be explained by th e initial dilution of absorbed Cs-137 in, the unlabelled seedling tiss ues. No correlation was found between K and Cs-137 distribution among ears, leaves, stems and roots in 64 old wheat plants. NH4 as a seconda ry N source in a nitrate nutrient solution marginally affected Cs-137 distribution.