Morphological Studies on Adventitious Root Formation in Cuttings

IV. Effects of IAA and NAA on Adventitious Root Formation in Cuttings

Abstract

The experiment was carried out to see the effects of basipetally moving endogenous substances on the root primordium differentiation of Portulaca cuttings and to determine whether the exogenously applied IAA or NAA acts as the substitute of the substances.
One side of the stem of the cutting was cut out at a slight distance from basal end for the purpose of blocking downward movement of root promoting substances, and then an agar block containing various concentrations of IAA or NAA was inserted into the cut-out portion. The experiments were conducted in two cases: one with leaves and the other without leaves.
Root initiation at the base of the cutting was observed morphologically in order to see the difference between the side under the cut and the intact side.
1. The formation of the root primordia was inhibited by removing the leaves from cuttings. Furthermore, the root primordia were not formed at all at the side under the cut portion, but the advancing tendency to form root primordia were somehow exhibited by the application of IAA or NAA to the cut-out portion.
2. On the cuttings with leaves, the formation of the root primordia was also inhibited at the side under the cut portion, but it was promoted a little by treatments with a low concentration of IAA or NAA.
3. On the cuttings with leaves, many root primordia were formed at the opposite side of the cut-out portion and a tendency to promote the formation of the root primordia was shown by the application of IAA to the cut-out portion. In this case, IAA at a concentration of 10-¹¹M was more effective than the other concentrations.
4. Most of the root primordia were formed near the cut-end of cuttings by IAA or NAA applied to the cut-out portion.
5. On the cuttings with leaves, IAA or NAA applied to the cut-out portion promoted the formation of the root primordia at the medullary ray.