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 DEVELOPMENTFACTORS 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.

Internal Biochemical &

Physical Processes

Growth&

Development

Heredity&

Environment

An Example: CHLOROPHYLL Production

Chlorophyll

Photosynthesis

Genes&

Light & Nutrients

Sugars

Growth & Development

Photosynthesis&

CO2, Light & Temp

PLANT HORMONESPHYTOHORMONES are Plant Growth

Regulators that PROMOTE or INHIBIT plant growth and developmentNot ENZYMESNot like ANIMAL HORMONES

3 PROPERTIESEffective in LOW CONCENTRATIONS (ppm)Can be TRANLOCATED from site of

SYNTHESIS to where it is ACTIVEEffects GROWTH and DEVELOPMENT

PHYTOHORMONES5 MAJOR PLANT HORMONE GROUPS

AUXINSCYTOKININS GIBBERELLINSABSCISSIC ACIDETHYLENE GAS

AUXINEFFECT

CELL DIVISION and ELONGATION @ stem and root tipsCELL 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

AUXINTYPES

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, D2, 4, 5, T MCPA

AUXIN and PLANT GROWTHINHIBITS ABSCISSION of leaves, flowers

and fruit

Stimulates ADVENTITIOUS ROOT growth

INHIBITS LATERAL BUD GROWTH through apical dominance

INHIBITS FLOWER INITIATION

Essential for FRUIT DEVELOPMENT

Responsible for TROPISMS (tropos = turn) or GROWTH CURVATURE due to differing elongation of cells

THIGMOTROPISM - response to TOUCHPHOTOTROPISM – response to LIGHTGEOTROPISM -response to GRAVITY

PHOTOTROPISM – response to LIGHT

GEOTROPISM - response to GRAVITY

CYTOKININSEFFECT – CELL DIVISION and

DIFFERENTIATION

PRODUCED mainly in ROOT TIPS (meristems, embryos, and fruits)

CONCENTRATION – in relation to AUXINHIGH CYTOKININ to AUXIN – produces SHOOT initiationLOW CYTOKININ to AUXIN produces ROOT initiationMOD to HIGH C & A produces CALLUS (undifferentiated

cells)

TRANSLOCATION – UP only, and side to side

CYTOKININS and PLANT GROWTHPromotes 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, ROOTSPrimarily CHLOROPLASTS of LEAVES

CONCENTRATION – increased concentrations provide increased growth

TRANSLOCATION – UP and DOWN, side to side

GIBBERELLINS and PLANT GROWTHSTEM ELOGATION – more than AUXIN

DEVELOPMENT and ELOGATION OF FLOWER STEMS

BREAKING DORMANCY in SEEDS and BUDS

FRUIT DEVELOPMENT – some speciesFLOWER DEVELOPMENT – some species

ABSCISSIC ACID - ABA

EFFECT – GROWTH INHIBITOR related to environmental STRESSCOUNTERACTS 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 metabolismNormally in GASEOUS STATE outside plantDISSOLVED in SOLUTION within plant

High AUXIN stimulates ETHYLENE production

PRODUCED in ACTIVELY GROWING MERISTEMSAGING FLOWERSRIPENING FRUITGERMINATING SEEDS

ETHYLENE and PLANT GROWTHStimulates FRUIT RIPENING

Promotes ABSCISSION of ORGANS leaves, flowers and fruit

Plants produce ETHYLENE in response to STRESSMay be involved in WOUND HEALING and

DISEASE RESISTANCE

FLOWERINGMECHANISM 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 FLORIGENEvidence for EXISTENCE does exist, but COMPOUND

has not been ISOLATEDIt may be a COMBINATION of HORMONES, therefore

not easy to DETECTCan be TRANSLOCATED