Understanding:
• Mitosis and cell division in the shoot apex provide cells needed for extension of the stem and development
of leaves
The apical meristems give rise to primary growth (lengthening) and occurs at the tips of the roots and shoots
- Growth at these regions is due to a combination of cell enlargement and repeated cell division (mitosis and cytokinesis)
- Differentiation of the dividing meristem gives rise to a variety of stem tissues and structures – including leaves and flowers
In the stem, growth occurs in sections called nodes – with the remaining meristem tissue forming an inactive axillary bud
- These axillary (lateral) buds have the potential to form new branching shoots, complete with leaves and flowers
Apical Growth in Shoots and Roots
Understanding:
• Plant hormones control growth in the shoot apex
The growth of the stem and the formation of new nodes is controlled by plant hormones released from the shoot apex
- One of the main groups of plant hormones involved in shoot and root growth are auxins (e.g. indole-3-acetic acid / IAA)
When auxins are produced by the shoot apical meristem, it promotes growth in the shoot apex via cell elongation and division
- The production of auxins additionally prevents growth in lateral (axillary) buds, a condition known as apical dominance
- Apical dominance ensures that a plant will use its energy to grow up towards the light in order to outcompete other plants
- As the distance between the terminal bud and axillary bud increases, the inhibition of the axillary bud by auxin diminishes
- Different species of plants will show different levels of apical dominance
The Role of Auxin in Apical Dominance
