Uptake of [3H]DHZ by tomato seedlings

[H-3]DHZ applied to intact roots of Lycopersicon esculentum seedlings was taken up faster from plants growing in soil than in liquid medium. However, subsequent export to the shoots was slower from roots growing in soil. Radioactivity was detected in an unlabelled medium Into which seedlings that had been cultured in labelled solution for three days were subsequently transferred. Radioactivity taken up by one half of a split-root system moved into the unlabelled root half and then into the unlabelled medium in which it was growing. The current results provide evidence for metabolism of cytokinins in various media, uptake from the media, subsequent transport and metabolism in the shoots. Of interest is that radioactivity was also released from the roots. There is clearly a need to pay greater attention to 'circulatory' movement of cytokinins between plant roots and the environment in which they are growing.