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How do auxins help control lateral branching and apical dominance?
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Plant development
The life cycle of the fern. (1) Clusters (sori) of sporangia (spore cases) grow on the undersurface of mature fern leaves. (2) Released from its spore case, the haploid spore is carried to the ground, where it germinates into a tiny, usually heart-shaped, gametophyte (gamete-producing structure), anchored to the ground by rhizoids (rootlike projections). (3) Under moist conditions, mature sperm are released from the antheridia and swim to the egg-producing archegonia that have formed on the gametophyte's lower surface. (4) When fertilization occurs, a zygote forms and develops into an embryo within the archegonium. (5) The embryo eventually grows larger than the gametophyte and becomes a sporophyte.
Auxins are a group of plant hormones that play a critical role in regulating plant growth and development, including the phenomenon of apical dominance.12
Apical Dominance and Lateral Branching
Apical dominance is the process by which the terminal (topmost) bud of a shoot inhibits the growth of lateral buds lower down on the stem. This mechanism is largely controlled by the flow of auxin produced in the shoot tip.34
- Inhibition: As auxin is transported downward from the terminal bud, it suppresses the development of axillary buds, maintaining the plant's characteristic single-trunk or primary growth form.45
- Release from Inhibition: When the terminal bud is removed, the source of this inhibitory auxin flow is eliminated. Consequently, the lateral buds are released from dormancy and begin to grow, often resulting in a bushier plant structure.45
While auxin is a primary factor, this process is also influenced by the plant's nutritional status and other hormones, such as cytokinins, which can promote the activity of lateral buds and counteract the inhibitory effects of auxin.4