Transcript Growth and development in plants

Growth and development
in plants
Response  Stimulus
 Results in survival of species
 respond by changing their growth pattern
 Tropism – growth toward or away from a
unidirectional stimulus, toward +, away 


Phototropism - light
Gravitropism - gravity
Thigmotropism – touch
 Reception  transduction  response
Nastic movements
 Movements that do not involve growth, not
dependent on direction of stimulus

Seismonastic movements – touching,
shaking, light or thermal stimulation




Mimosa plant, prayer plant
Changes in turgor pressure, K+
Circadian rhythm – biological rhythm with 24
hours cycle
Biological clock – mechanism by which the
biological rhythm is maintained
Plant Hormones
 Chemical signals produced in very low
concentrations for communication
Auxin
 affect many aspects of plant growth and development
 Indoleacetic acid(IAA) most common occurring
 Apical dominance – prevents lateral buds
 Promotes root growth if applied
 Promotes growth of fruit
 Induce development of fruit without pollination
 Weed control (Agent Orange)
 Gravitropism and phototropism
nd messengers lead to
 moves to shady side, 2
production of growth factors, elongation of stem on
shady side, bends toward light
Gibberellins
 Growth promoting hormones
 Gibberellic acid (GA)
 Stem elongation (bush beans to pole beans)
 Used to break dormancy, bring on onset of
flowers
 Induce growth of plants and increase size of
flowers
cytokinins
 Promote cell division, derivative of adenine

Occur n actively dividing tiwwues of roots,
seeds and fruits
 Used to prolong life of flower cuttings and
vegetables in storage
 Senescence – aging process, loss of leaves

Can be prevented by applying cytokinins
Abscisic Acid (ABA)
 Stress hormone
 initiates and maintains seed and bud
dormancy
 Stimulates closure of stomata when in water
stress
 Natural progression in Fall for plants, levels
decrease in spring (gibberellins increase)
 Abscission – dropping of leaves, fruit,
flowers if applied externally, not naturally
Ethylene
 Involved in abscission, stimulates enzymes
which cause leaves, fruit or flowers drop
 Used to speed up ripening of fruit
 Applied to citrus to keep color
 Release gas at wound, speeds up ripening of
fruit around fruit
Photoperiodism
 Physiological response prompted by changes
of length of day or night



Germination – breaking of bud dormancy
Can influence flowering
3 groups of flowering plants



Short day – day length 14 hours or shorter
Long day – 14 hours or longer
Day neutral - not dependent on day length
 If dark period is interrupted, flowering will not
result, not the same result if reversed
Phytochrome
 blue/green leaf pigment,




has 2 forms that absorbs red light at different
wavelengths
Phytochrome red – 660 nm
Phytochrome far-red – 730 nm
Allows a plant to detect photoperiod changes
 Other functions of phytochrome


Promotes seed germination
Inhibits stem elongation