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

• 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

• Male sterility for hybrid seed production• Fruit ripening• Senescence• Delaying seed pod splitting• Flowering