Plant branching is a process regulated by phytohormones produced by the plant, similar to hormones found in animals. Many scientists have believed that auxin, the most intensely studied plant phytohormone, is the most important factor that controls branching. Researchers at Texas A&M University have found that abscisic acid (ABA), more known for its role in regulating water movement in plants, also plays an important role in plant branching.

Branching is controlled by light signals modified by neighboring plants. The stem grows taller if the branches are inhibited. The plant invests in the main shoot rather than in branching, to get to more direct light. The study examined plant mechanisms used to control branching in crowded and uncrowded conditions.

The researchers found that when given light signals that mimic crowded and uncrowded conditions, bud growth is altered very quickly, within six hours, when light signals are changed. They also found that changes in bud growth were more closely related to changes in ABA than auxin. ABA is one of the earliest regulators of branching. Auxin regulates from the stem, but ABA is present in the bud and is probably responding more directly to light signals that it receives.

For more details about this research, read the article at AgriLife Today.

Figure: This Arabidopsis plant highlights the branching that can be inhibited by abscisic acid. (Texas A&M AgriLife photo by Dr. Scott Finlayson)