Yao, Chi (2013-12). Abscisic Acid Regulation of Branching. Master's Thesis.
Axillary meristem production and activity contribute to the high plasticity of plant development which allows plants to respond to environmental changes. Branches arise from axillary buds that form in the leaf axil. These buds may remain dormant, or may grow out to form branches immediately. Alternatively, the axillary buds may also persist in a dormant state for an indefinite period of time until appropriate signals permit outgrowth to commence. Branching is regulated by phytohormones, including auxin acting via the polar auxin transport stream, and locally within the bud by the action of branching integrators like BRC1and MAX2. Branchingis also regulated by environmental factors such as competition signals (low Red light: Far-Red light [R: FR])that inhibit bud outgrowth. Our recent studies indicate that ABA acts within the bud tosuppress outgrowth. NCED3 is a key enzyme in the ABA biosynthesis pathway, and ABA2 is another importantABA biosynthesisgene.ABA accumulatedtosignificantly higher levels in lower, more dormantbudscompared to less dormant buds at higher rosette positions. Additionally, bud ABA content and the correlative inhibition index, whichis a measure of systemic branching suppression, were increased in plants grown under low R:FR compared to those grown under high R:FR. Under low R:FR the NCED3 deficient mutantnced3-2and the ABA2 deficient mutant aba2-1had significantly more branches and lower correlative inhibition index thanWT. The results indicate that the suppression of branching by low R:FR may be mediated, at least in part, by elevated levels of ABA in the buds.