The final exam takes place in KIN 1024 Thursday May 2nd at 10am It consists of 40 questions 10 from each topic 17 18 19 20 Good Luck Hormones Topic 17 1 a What are characteristics of plant hormones b Why should hormones be considered regulators rather than stimulators c What determines the effect that a hormone has on a tissue d Are all tissues equally sensitive to hormones at all times in the lifespan of a plant A Hormone Chemical signals that plants and other multi celled organisms use to regulate and coordinate metabolism growth and morphogenesis Generally Synthesis of hormone in one part of the body then transported to another part of the body where it elicits a specific response Related to plants used to broadly include chemical signals that act within the SAME tissue in which they are produced o ex ethylene diffuses from site of synthesis affecting nearby cells Hormones exist in two forms Unconjugated form Hormone is ACTIVE as it does o Typically only a fraction of hormone is in unconjugated form Conjugated form Hormone is INACTIVE o Majority hormones o Bound to substances such as sugars amino acids peptides and proteins that inactivate it B Hormones should be considered regulators rather than stimulators because they do NOT always stimulate growth sometimes they suppress activity Ex In apical dominance auxin produced by the apical meristem o maintains the axillary buds in a dormant state iClicker WILL be one exam In apical dominance the apical bud Inhibits the growth of axial buds Apical dominance is the apical meristem telling the rest of the plant to not develop axial buds yet and to focus on its own development instead C Factors that determine the effect that a hormone has on a tissue Amount of the hormone Sensitivity The ability to recognize the hormone o This varies with specifc tissues and with developmental stages of the tissue D All tissues are NOT equally sensitive to hormones at all times in the lifespan of a plant May be sensitive in one stage and not in the other 2 What are the six major groups of plant hormones a How did they get their names b What are the sites of biosynthesis of each of these c How are they transported to other parts of the plant d What are the major effects caused by each of these How do we use application of the major hormones to our advantage particularly in agriculture How do we use mutations in hormone production or sensitivity to our advantage particularly in agriculture E 6 major groups of plant hormones 1 AUXINS Darwin brothers did experiments and found that when seedlings are freely exposed to a lateral light some influence is transmitted from the upper to the lower part causing the lower part to bend iClicker How might a plant axis bend Cell elongation cell size increase on side away from the light due to the activity of Auxin Or cells shrinking on the side that bends a Origin of name Named auxin from the Greek auxein meaning to increase The cells on the side of the coleoptile with increased auxin concentrations increase in length b Sites of biosynthesis All plant tissues can produce auxin However synthesized primarily in the shoot apical meristem young leaves and developing fruits and seeds c Transport Auxin is the ONLY plant hormone that is transported POLARLY unidirectional Structural polarity of embryogenesis and later development is traceable to polar unidirectional transport of auxin Basipetal Towards the BASE Center of the seedling Acropetal Towards the APEX iClicker If the flow is basipetal in the shoot and root what direction does it go in this root Picture on slide 19 Root is oriented vertically UP moving towards the base of the root not the base of the plant Two basic systems for auxin transport in cells 1 Energy requiring unidirectional POLAR transport system Influx carriers are at one end of the cell Eflux carries are at the other 2 Passive nonpolar transport system via the phloem Root tip is NOT a primary site of auxin synthesis Auxin arrives in the phloem from sites of synthesis d Major effects uses 1 Stimulates differentiation of vascular tissue Auxin flows around a wound and replaces lost tissue 2 Plays a role in the induction and arrangement of leaves 3 In woody plants promotes activity of the vascular cambium Auxin is synthesized by expanding buds These two things are correlated because the activity of these buds is at the beginning of the growing season also when the vascular cambium must ramp up activity again Application to our advantage Mutations to our advantage 4 Commercial use Promotes formation of lateral roots by stimulating the pericycle and adventitious stem or leaf borne roots 5 Auxin promotes fruit development From above Developing seeds synthesize auxin In a strawberry that has had auxin removed the receptable does NOT form red fleshy part of the aggregrate fruit Parthenocarpic Fruits Fruits produced without fertilization Result from auxin application 6 Application of synthetic auxin is used to kill weeds It has a differential effect on grasses vs other plants that is related to the ability of grasses to rapidly inactivate synthetic auxins by conjugation 2 CYOTKINS a Origin of name Found as a growth factor in coconut milk that accelerated plant embryo growth and promoted growth of isolated tissues and cells in test tubes Named cytokine because of interest in its effects on cytokinesis b Site of biosynthesis Root tips c Transport Transported in the xylem from the roots to the shoot Why aren t they transported via the phloem from the root The flow is in the other direction d Effects 1 Auxin cytokine concentrations help maintain a healthy ratio of shoot to root tissue If 1 1 concentration tissues remain meristematic If auxin only Roots form If cytokine only Buds form iClicker The ratio of auxin to cytokinin is important in maintaining a healthy ratio of shoot to root tissue Auxin is produced primarily in the shoot and cytokinin is produced primarily in the root When tobacco pith callus a mass of meristematic cells is treated with higher concentrations of auxin than cytokinin is are formed ROOTS 2 Delay leaf senescence Ex When a gene for cytokinin synthesis in older leaves is inserted in Tobacco leaves senesce much later Plant cells totipotent this combined with cytokinin is important to tissue culture methods 3 ETHYLENE A gaseous hydrocarbon a Origin of name In 1800 s leaks of gas from city street light was observed to cause defoliation of street trees In 1901 ethylene was shown to be the chemical
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