The Genetic Basis of Growth and
Development
Plants are made up of
• cells
• tissues
• organs
Plants have specialized tissues
called meristems
• Shoot apical meristem
(SAM)
• Intercalary meristem
• Root apical meristem
(RAM)
• Lateral meristems:
pericycle, vascular
cambium
Plants grow by cell
• division
• expansion
• differentiation
Plant development is controlled
by hormones
• Auxin:stimulates growth and cell division
• Gibberellins:stimulates stem growth and
seed germination
• Cytokinins:regulates cell division and
senescence
• Abscisic Acid:responds to osmotic stress,
inhibits germination, closes guard cells
More Hormones
• Ethylene:regulates fruit ripening and
flowering, responds to stress
• Jasmonic Acid:responds to insect attacks
turning on plant defenses
• Brassinosteroids: affect stem elongation,
pollen tube growth, leaf bending and xylem
differentiation
Plant development is affected by
the environment
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Phototropism (light)
Gravitropism (gravity)
Thigmotropism (touch)
Nyctinastic movement (light)
Thigmonastic movement (mechanical)
Environmental Influences
• Circadian Rhythms (biological clocks set by
light)
• Dormancy (temperature, light & water)
• Vernalization (cold induction of flowering)
• Stratification (cold induction of
germination)
• Photoperiodism (germination and
flowering)
Photoperiodic regulation of
flowering
Genetic control of flowering
Signal transduction by hormones
or environmental signals
Genetic modification can redirect
developmental processes
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Male sterility for hybrid seed production
Fruit ripening
Senescence
Delaying seed pod splitting
Flowering