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4.3 Plant Growth and Development
Seed Germination
Definition:
The development of a seed embryo into a seedling.
Types:
Hypogeal:
Cotyledons remain below ground (e.g., Pea).
Epigeal:
Cotyledons are pushed above ground (e.g., Bean).
Viviparous:
Germination on the parent plant (e.g., Mangroves).
Growth
Phases in Meristems:
Meristematic:
Cell division.
Elongation:
Cell enlargement.
Maturation:
Cell differentiation.
Measurement:
Can be measured using an
auxanometer
.
Differentiation & Related Processes
Differentiation:
Cells mature to perform specific functions.
Dedifferentiation:
Differentiated cells regain the ability to divide.
Redifferentiation:
Dedifferentiated cells mature into new specialized cells.
Plant Hormones (PGRs)
Chemical messengers that regulate plant growth and development.
Five Major Types:
Auxins, Gibberellins, Cytokinins, Ethylene, Abscisic Acid.
Auxin
Key Functions:
Apical Dominance:
Promotes the growth of the main stem.
Cell Elongation:
Lengthens cells.
Root Initiation:
Promotes root formation.
Parthenocarpy:
Fruit development without fertilization.
Gibberellins (GAs)
Key Functions:
Stem Elongation:
Especially in dwarf plants.
Bolting:
Internode elongation before flowering.
Seed Germination:
Breaks dormancy.
Fruit Development:
Improves fruit size and shape.
Cytokinins
Key Functions:
Cell Division (Cytokinesis):
Promotes cell proliferation.
Overcoming Apical Dominance:
Promotes lateral bud growth.
Delaying Senescence:
Keeps leaves and flowers fresh.
Ethylene
Key Functions:
Fruit Ripening:
The "ripening hormone."
Senescence and Abscission:
Promotes aging and shedding of parts.
Flowering:
Induces flowering in some plants (e.g., pineapple).
Abscisic Acid (ABA)
Key Functions:
Stomatal Closure:
Conserves water during stress.
Seed Dormancy:
Prevents germination in unfavorable conditions.
Stress Hormone:
Helps plants tolerate drought, salinity, etc.