PLANT GROWTH and DEVELOPMENT 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 ENVIRONMENT Lots of factors including - COMPETITION, SOIL, TEMP, LIGHT, PREDATION by insects, disease, parasites, etc.

An Example: CHLOROPHYLL Production

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 CONCENTRATION EFFECT PRODUCED in ACTIVELY GROWING PLANT PARTS 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