1995. Effect of apex excision and replacement by l-naphthylaeetic acid on cytokinin eoneentration and apical dominance in pea plants. As known from literature lateral buds from pea (Pisum sativum) plants are released from apical dominance when repeatedly treated with exogenous cytokinins. Little is known, however, about the endogenous role of cytokinins in this process and whether they interact with basipolar transported !AA, generally regarded as the main signal controlling apical dominance. This paper presents evidence that sueh an interaction exists. The excision of the apex of pea plants resulted in the release of inhibited lateral buds from apical dominance (AD). This could be entirely prevented by applying 1-naphthylacetic acid (NAA) lo the cut end of the shoot. Removai of the apex also resulted in a rapid and rather large increase in the endogenous concentrations of zeatin riboside (ZR), isopentenyladenosine (iAdo) and an as yet unidentified polar zeatin derivative in the node and intemode below the point of decapitation. This accumulation of ZR and iAdo, was strongly reduced by the application of NAA. The observed increase in cytokinin concentration preceded the elongation of the lateral buds, suggesting that endogenous cylokinins piay a significant role in Ihe release of lateral buds from AD. However, the effect of NAA on the concentration of cytokinins clearly demonstrated the dominant role of the polar basipetally transported auxin in AD. The results sugges! a mutual interaction between the basipolar lAA transport system and cytokinins obviously produced in the roots and transported via the xylem into the stem of the pea plants.