EFFECT OF APEX EXCISION AND REPLACEMENT BY 1-NAPHTHYLACETIC ACID ON CYTOKININ CONCENTRATION 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 exogen ous cytokinins. Little is known, however, about the endogenous role of cytokinins in this process and whether they interact with basipolar t ransported IAA, generally regarded as the main signal controlling apic al dominance. This paper presents evidence that such an interaction ex ists. The excision of the apex of pea plants resulted in the release o f inhibited lateral buds from apical dominance (AD). This could be ent irely prevented by applying 1-naphthylacetic acid (NAA) to the cut end of the shoot. Removal of the apex also resulted in a rapid and rather large increase in the endogenous concentrations of zeatin riboside (Z R), isopentenyladenosine (iAdo) and an as yet unidentified polar zeati n derivative in the node and internode below the point of decapitation . This accumulation of ZR and iAdo, was strongly reduced by the applic ation of NAA. The observed increase in cytokinin concentration precede d the elongation of the lateral buds, suggesting that endogenous cytok inins play a significant role in the 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 au xin in AD. The results suggest a mutual interaction between the basipo lar IAA transport system and cytokinins obviously produced in the root s and transported via the xylem into the stem of the pea plants.