Rooting Cofactors: Past, Present, and Future
Charles E. Hess
Research to find substances that may be responsible for root initiation has been underway for over 100 years. The presence of leaves and buds have been shown to have a promotive effect on root initiation. If leaves and/or buds are removed or if the stem is girdled, rooting decreases. The effect of girdling the stem indicates that the root-promoting substances are transported in the phloem. Sugars and nitrogenous substances certainly play a role and the beneficial effects of leaves can, in part at least, be replaced by supplying leafless cuttings sugars and amino acids.
The discovery of auxin, indole-3-acetic acid (IAA), in the 1930s and its ability to stimulate root initiation demonstrated that a hormonal substance or rhizocaline was involved in the process of root initiation. The synthesis of compounds, such as, indolebutyric acid (IBA) and naphthaleneacetic acid (NAA), provided plant propagators with compounds that could increase the range of plants propagated by cuttings, shorten
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