Apical Dominance Control in Ipomoea nil: The Influence of the Shoot Apex, Leaves and Stem

The outgrowth of lateral buds is known to be controlled by the upper shoot tissues, which include the apex, the young leaves and the upper stem. An analysis of the influence of these plant parts on axillary bud elongation in Ipomoea nil was carried out by various treatments on these specific tissues. A restriction of elongation in the main shoot due to either decapitation or shoot inversion resulted in the release of apical dominance A non-linear type of compensating growth relationship was observed between the 13 cm apical growing region of the stem and the lateral buds. It was determined by decapitation, defoliation and AgNO3 treatments that both the 13 cm stem-growth region and the young leaves (1–5 cm in length) had a much greater inhibitory influence on the outgrowth of specified lateral buds than did the stem apex (consisting of the terminal 0.5 cm of the shoot). The specified lateral buds which were analyzed for outgrowth were located a number of nodes below the shoot apex. The intervening nodes were debudded. Although the importance of young leaves in the control of apical dominance has been previously recognized, the most significant result from the present study with Ipomoea was the strong influence of the 13 cm apical growth region of the stem on the out growth of the lateral buds.