DEVELOPMENTAL EFFECTS OF 24-EPIBRASSINOLIDE IN EXCISED ROOTS OF TOMATO GROWN-INVITRO

The effects of 1 pM-10 muM 24-epibrassinolide presented to apical and basal regions of excised roots of tomato (Lycopersicon esculentum Mill . cv. Best of All) grown aseptically in a two-well culture vessel have been investigated. Only inhibitory effects were observed and only at 0.1 muM or greater. At 10 muM basally- and apically-applied epibrassin olide inhibited growth in apical regions, but not in basal regions. Lo wer concentrations (1 and 0.1 muM) also inhibited growth, again only i n apical regions and usually only when presented directly to those reg ions. Cultured tomato roots therefore appear to transport epibrassinol ide acropetally, but whether they do so basipetally is not yet clear. The reduced responsiveness to epibrassinolide observed in roots grown by this method is thought to be due to the larger inoculum used rather than the physiological age of the roots. There was some evidence that the sensitivity of cultured roots to epibrassinolide is directly rela ted to growth rate.