1. PLANT GROWTH and DEVELOPMENT
Phytohormones

2. PLANT GROWTH and DEVELOPMENT
SEPARATE, but INTERELATED PROCESSES
GROWTH
increase in SIZE and WEIGHT, measurable
DEVELOPMENT
DIFFERENTIATION of cells, tissues and organs

3. PLANT GROWTH and DEVELOPMENT
FACTORS determining GROWTH and DEVELOPMENT
HEREDITY
All CELLS contain a full compliment of GENETIC INFORMATION or CODE
Through process of DIFFERENTIATION only a FEW will be EXPRESSED
ENVIRONMENT
Lots of factors including - COMPETITION, SOIL, TEMP, LIGHT, PREDATION by insects, disease, parasites, etc.

4. An Example: CHLOROPHYLL Production

5. PLANT HORMONES
PHYTOHORMONES are Plant Growth Regulators that PROMOTE or INHIBIT plant growth and development
Not ENZYMES
Not like ANIMAL HORMONES
3 PROPERTIES
Effective in LOW CONCENTRATIONS (ppm)
Can be TRANLOCATED from site of SYNTHESIS to where it is ACTIVE
Effects GROWTH and DEVELOPMENT

6. PHYTOHORMONES 5 MAJOR PLANT HORMONE GROUPS AUXINS CYTOKININS
GIBBERELLINS
ABSCISSIC ACID
ETHYLENE GAS

7. AUXIN CONCENTRATION EFFECT PRODUCED in ACTIVELY GROWING PLANT PARTS
CELL DIVISION and stem and root tips
CELL DIFFERENTIATION
PRODUCED in ACTIVELY GROWING PLANT PARTS
APICAL MERISTEMS of shoots
YOUNG leaves, flowers, fruits, embryos, pollen
CONCENTRATION
Too much – INHIBITORY or TOXIC
Too little – NOT ENOUGH GROWTH
OPTIMAL CONCENTRATION – concentration of hormone that promotes the MAXIMUM GROWTH
CONCENTRATION EFFECTS differ in ROOTS and SHOOTS
TRANSLOCATION – DOWN, and side to side
The FARTHER from TIP the LOWER the concentration

8. AUXIN TYPES IAA – indole 3 acetic acid (natural)
PAA – phenylacetic acid (natural and synthetic)
IBA – indole butyric acid (natural and synthetic)
NAA – napthalene acetic acid (synthetic)
2, 4, D
2, 4, 5, T
MCPA

9. AUXIN and PLANT GROWTH
INHIBITS ABSCISSION of leaves, flowers and fruit
Stimulates ADVENTITIOUS ROOT growth
INHIBITS LATERAL BUD GROWTH through apical dominance
INHIBITS FLOWER INITIATION
Essential for FRUIT DEVELOPMENT

10. AUXIN and PLANT GROWTH
Responsible for TROPISMS (tropos = turn) or GROWTH CURVATURE due to differing elongation of cells
THIGMOTROPISM - response to TOUCH
PHOTOTROPISM – response to LIGHT
GEOTROPISM -response to GRAVITY

11. THIGMOTROPISM - response to TOUCH

12. PHOTOTROPISM – response to LIGHT

13. GEOTROPISM - response to GRAVITY

14. CYTOKININS EFFECT – CELL DIVISION and DIFFERENTIATION
PRODUCED mainly in ROOT TIPS (meristems, embryos, and fruits)
CONCENTRATION – in relation to AUXIN
HIGH CYTOKININ to AUXIN – produces SHOOT initiation
LOW CYTOKININ to AUXIN produces ROOT initiation
MOD to HIGH C & A produces CALLUS (undifferentiated cells)
TRANSLOCATION – UP only, and side to side

15. CYTOKININS and PLANT GROWTH
Promotes SHOOT INITIATION – tissue culture
Promotes BRANCHING – counteracts AUXINS and apical dominance
PREVENTS LEAF AGING and DEATH
delays degrading of chlorophyll
BREAKS DORMANCY in light requiring seed
Development of PISTILLATE FLOWERS

16. GIBBERELLINS (GA) EFFECT – CELL ELONGATION @ internodes PRODUCED
In ACTIVELY GROWING tissues, ROOTS
Primarily CHLOROPLASTS of LEAVES
CONCENTRATION – increased concentrations provide increased growth
TRANSLOCATION – UP and DOWN, side to side

17. GIBBERELLINS and PLANT GROWTH
STEM ELOGATION – more than AUXIN
DEVELOPMENT and ELOGATION OF FLOWER STEMS
BREAKING DORMANCY in SEEDS and BUDS
FRUIT DEVELOPMENT – some species
FLOWER DEVELOPMENT – some species

18. ABSCISSIC ACID - ABA
EFFECT – GROWTH INHIBITOR related to environmental STRESS
COUNTERACTS effects of AUXIN, GIBBERELLINS, CYTOKININS
PRODUCTION - synthesized in PLASTIDS of mature leaves
TRANSLOCATION – UP and DOWN, side to side

19. ABSCISSIC ACID and PLANT GROWTH
Stimulates AGING, SENESCENCE
Stimulates DORMANCY in SEEDS and BUDS
CLOSING of STOMATA – triggers closing when water levels low (originates in roots and translocates up) when plant can’t keep up with transpiration

20. ETHYLENE C2H4 – natural product of plant metabolism
Normally in GASEOUS STATE outside plant
DISSOLVED in SOLUTION within plant
High AUXIN stimulates ETHYLENE production
PRODUCED in ACTIVELY GROWING MERISTEMS
AGING FLOWERS
RIPENING FRUIT
GERMINATING SEEDS

21. ETHYLENE and PLANT GROWTH
Stimulates FRUIT RIPENING
Promotes ABSCISSION of ORGANS leaves, flowers and fruit
Plants produce ETHYLENE in response to STRESS
May be involved in WOUND HEALING and DISEASE RESISTANCE

22. FLOWERING
MECHANISM for response to LIGHT and INDUCING FLOWERING is not known
PHYTOCHROME and CRYPTOCHROME pigments involved
Some plants INITIATE FLOWERING in response to CHANGING LENGTH of LIGHT – PHOTOPERIODISM
LIGHT induces plant to CHANGE MERISTEMATIC TISSUE to form FLOWERS
FLOWERING HORMONE named FLORIGEN
Evidence for EXISTENCE does exist, but COMPOUND has not been ISOLATED
It may be a COMBINATION of HORMONES, therefore not easy to DETECT
Can be TRANSLOCATED