Phytohormones
PLANT GROWTH and DEVELOPMENT
 SEPARATE, but INTERELATED PROCESSES
 GROWTH

increase in SIZE and WEIGHT, measurable
 DEVELOPMENT

DIFFERENTIATION of cells, tissues and organs
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
Heredity
&
Environment
Internal Biochemical
&
Physical Processes
 ENVIRONMENT
 Lots of factors including COMPETITION, SOIL, TEMP,
LIGHT, PREDATION by insects,
disease, parasites, etc.
Growth
&
Development
An Example: CHLOROPHYLL Production
Genes
&
Light & Nutrients
Growth & Development
Sugars
Chlorophyll
Photosynthesis
Photosynthesis
&
CO2, Light & Temp
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
PHYTOHORMONES
 5 MAJOR PLANT HORMONE GROUPS
 AUXINS
 CYTOKININS
 GIBBERELLINS
 ABSCISSIC ACID
 ETHYLENE GAS
AUXIN
 EFFECT
 CELL DIVISION and ELONGATION @ 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
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
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
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
THIGMOTROPISM - response to TOUCH
PHOTOTROPISM – response to LIGHT
GEOTROPISM - response to GRAVITY
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
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
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
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
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
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
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
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
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