Reviving a Forgotten Theory of Apical Dominance in Plants: Kebrom Publishes New Work

Tesfamichael Kebrom Ph.D.The shoot architecture of plants is a major factor determining the yield of crops. Optimal shoot architecture also enhances the esthetic values of ornamental plants. The number of branches developed and their position determines the shoot architecture. Branches develop from buds at the leaf-stem junctions. In some plants, the buds do not grow, and thus become dormant, because the shoot tip synthesizes the plant hormone auxin that suppresses the growth of the buds.

Gardeners normally prune the shoot tips of plants to induce the dormant buds grow and form branches. However, manual removal of shoot tips to optimize branching is tedious, time consuming, expensive and almost impossible in some of the major field crops. Therefore, plant scientists are interested in breeding plants that inherently develop optimal number of branches, which requires an in-depth knowledge of the regulation of dormancy and growth of buds. The inhibition of the growth of buds by the shoot tip is known as apical dominance. Plant biologists have been investigating the phenomenon of apical dominance for over a century. Three theories, direct, diversion and indirect, were proposed in the 1930s to explain how auxin synthesized in the shoot tip inhibits the growth of branches. The direct and diversion theories of apical dominance were investigated in detail and are now replaced with the current auxin transport canalization and second messenger theories, respectively. However, the two current theories cannot entirely explain the phenomenon of apical dominance.

The third, indirect, theory that explains apical dominance as auxin from the shoot tip promotes stem growth and a growing stem somehow inhibits bud outgrowth has been completely forgotten. However, Dr. Tesfamichael Kebrom, a plant physiologist at CARC, provides new insights into the indirect theory in a new paper published in the journal Frontiers in Plant Science. The new insights initially emerged from a paper on shoot branching in wheat published in the journal Plant Physiology (Kebrom et. al., 2012; 112.197954.) while Kebrom was working as a postdoctoral fellow at the Commonwealth Scientific and Industrial Research Organization (CSIRO) in Australia. In this newly published work, Kebrom elucidated the indirect theory of apical dominance as auxin promotes the growth of the stem, and a growing stem, which is a strong consumer of sugar, inhibits buds indirectly by depriving sugars necessary for their growth.

Dr. Kebrom further highlighted the need for a more detailed study of the indirect theory to better understand the physiological and molecular basis of apical dominance and shoot branching in plants. Details on this published work can be found at this link:

Dr. Ali Fares
Ali Fares Ph.D.
Associate Director for Research
(936) 261-5019


Tesfamichael Kebrom Ph.D.
Post-Doctoral Researcher
(936) 261-5051