growth and development in plants. response stimulus results in survival of species respond by...
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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
moves to shady side, 2nd messengers lead to 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