juvenility and flower bud differentiation
Juvenility in Plants
Definition:
Juvenility is the non-flowering phase of a plant’s growth cycle that begins after seed germination and ends when the plant becomes capable of flowering. During this phase, plants exhibit unique growth and morphological characteristics.
The length of juvenility varies between plant species:
- Annual plants: Have a short juvenile period.
- Perennial plants: Exhibit a longer juvenile phase, which may span several years.
Characteristics of Juvenility
Leaf Form:
- In juvenile stages, the leaves are highly active and may differ in morphology from mature leaves.
- Example: Acacia species display distinct leaf forms during their juvenile phase.
Growth Form:
- Juvenile branches often grow straight and parallel to the main stem, forming whip-like structures.
- Example: Citrus and guava produce these juvenile branches, referred to as water sprouts.
Presence of Thorns:
- Juvenile stages of certain fruit trees exhibit thorns, which disappear as the plants mature.
- Examples: Apple, pear, and citrus trees.
Leaf Retention: Juvenile plants retain their leaves throughout the year, while mature plants shed leaves periodically.
Root Emergence: Juvenile plant parts used in propagation exhibit rapid root development.
Flower Bud Differentiation
Definition:
Flower bud differentiation is the process by which vegetative buds transform into reproductive (flowering) buds. This transformation involves physiological and cellular changes in the apical meristem, resulting in the formation of flowers or inflorescences.
Phases of Flower Growth
Flower Bud Differentiation (Induction): Initiated by increased cell division beneath the apical meristem. Parenchyma cells surrounding the meristem divide and develop into flower primordia.
Initiation: During this phase, the development of flower structures begins.
Development of Flowers: This phase spans from flower bud differentiation to blooming. It concludes with anthesis—the opening of flowers, making them available for pollination.
Key Note: A flower is essentially a modified reproductive branch, originating from an apical meristem that produces leaf primordia.
Types of Buds
Simple Bud: Develops into vegetative branches. Commonly referred to as a leaf bud.
Mixed Bud: Produces both vegetative growth and flowers. Often termed a flower-bearing stalk or flower bud.
Compound Bud: Gives rise to both leaves and flowers.
Factors Influencing Flower Bud Formation
Vegetative Stage:
- A plant must achieve a specific vegetative maturity before flowering.
- Example:
- Cox’s Orange Pippin apple requires 20 nodes.
- Golden Delicious apple requires 16 nodes.
Hormonal Balance: Hormones such as gibberellins, cytokinins, and auxins regulate bud differentiation and flower formation.
Nutrient Distribution: Redistribution of nutrients within the apical meristem influences the initiation and development of flower buds.
Timing of Bud Development: Flower buds do not develop uniformly across the tree. Example: In apple trees, terminal buds on spurs begin differentiation 4-6 weeks earlier than lateral buds.
