PLANT GROWTH and DEVELOPMENT Phytohormones PLANT GROWTH and

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 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 & CO 2, 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 �C 2 H 4 – 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