Mills AP Bio 2003/2013 Chapter 26 Control of Plant Growth Responses in Flowering Plants Read Ch 26 in Textbook Read pg in Cliffs AP Book

Mills AP Bio 2003/2013 Topics –26.1 Plant Hormones –26.2 Plant Responses Chapter 26 Control of Plant Growth Responses in Flowering Plants Overview

Mechanism of action – hormones –Receptor –Transduction pathway –Cellular response Mills AP Bio 2003/2013 Chapter 26 Control of Plant Growth Responses 26.1 Plant Hormones

Second Messenger Animation Mills AP Bio 2003/2013

Groups of Plant Hormones –Auxins –Gibberellins –Cytokinins –Inhibitory hormones –Hormones work together to cause various effects

Mills AP Bio 2003/2013 Chapter 26 Control of Plant Growth Responses 26.1 Plant Hormones Auxins –Most common auxin is indoleacetic acid(IAA) –Prevent growth of axillary buds  supports apical dominance –Promotes adventitious root growth (roots from stem) –Promotes root branching –Auxins produced by seeds promote growth of fruit. If auxins high in fruits and low in stems and leaves, fruit won’t fall off. –Promote phototropism and gravitropism

Chapter 26 Control of Plant Growth Responses 26.1 Plant Hormones Mills AP Bio 2003/2013 How Auxins work –Auxin binds to receptors on cell membrane –Activates ATP driven proton (H + ) pump –Pumps H ions into space between cell membrane and cell wall. –H ions (acid) weaken cell wall. –Gradient set up that pulls solutes then water into cell causing it to swell –Pushes on cell wall –Cell elongates

Mills AP Bio 2003/2013 Gibberellins –About 70 different gibberellins, GA 3 the most common –Promote stem elongation especially in dwarf plants –Can break dormancy in seeds and buds –Sources: young leaves, roots, embryos, seeds, fruits Chapter 26 Control of Plant Growth Responses 26.1 Plant Hormones

Mills AP Bio 2003/2013 How Gibberellins work –Gibberellin binds to a receptor on the cell membrane –Activates a second messenger inside the cell – Ca ++ –Ca ++ combines with a protein called calmodulin –This complex activates the gene that codes for amylase –Amylase acts on starch to release sugars Chapter 26 Control of Plant Growth Responses 26.1 Plant Hormones

Mills AP Bio 2003/2013 Cytokinins(remember cytokinesis?) –Derivatives of adenine Zeatin Kinetin –Promote cell division and differentiation –Prevent senescence (aging process) In senescence, large molecules in the plant are broken down Can lead to leaf loss etc Cytokinins inhibit leaf death and can promote leaf growth –Varying ratios of cytokinins and auxins can effect how plant differentiates In tissue culture: Auxin and cytokonins in usual amounts – tobacco strip develops into undifferentiated callous. If ratio of auxin to cytokinins is appropriate, the callous produces shoots. A different ratio promotes vegetative shoots and leaves. A different ratio promotes floral shoots. Chapter 26 Control of Plant Growth Responses 26.1 Plant Hormones

Mills AP Bio 2003/2013 Inhibitory Hormones –Abscisic acid (stress hormone) Promotes bud and seed dormancy Closes stomates(when water supply low) by causing K + to leave guard cells Inhibits gibberellins (which break dormancy) Produced by any “green tissue” with chloroplasts, by endosperm and by roots. Abscission=dropping of leaves, fruit and flowers from plants –Originally thought that abscisic acid caused this – now believe it is ethylene –Ethylene Induces leaf, flower and fruit abscission (falling off) Promotes fruit ripening-increases activity of enzymes that soften fruit (ex. cellulase) Gas released from fruit (wound?) Chapter 26 Control of Plant Growth Responses 26.1 Plant Hormones

Mills AP Bio 2003/2013 Functions of Plant Hormones Hormone Function – all of these hormones work together Auxins Stimulate growth Involved in stem and root cell elongation in phototropism and gravitropism Gibberellins Stimulate growth especially stems, especially in dwarf plants. Can break seed and bud dormancy Cytokines Stimulate growth by causing cell division Abscisic Acid Inhibit growth Causes stomates to close Maintains seed and bud dormancy Ethylene Inhibit growth Causes fruit to ripen and fall Chapter 26 Control of Plant Growth Responses 26.1 Plant Hormones

Mills AP Bio 2003/ Plant responses –Tropisms –Nastic movements Tropisms –Plant growth toward (positive) or away (negative) from a stimulus –Reception  transduction  response –Common tropisms Phototropism Gravitropism Thigmotropism Chapter 26 Control of Plant Growth Responses 26.2 Plant Responses

Mills AP Bio 2003/2013 Phototropism –Cells on dark side of plant grow faster, so plant bends toward the light – positive phototropism –Pigment related to riboflavin acts as a receptor which somehow causes the release of the hormone auxin, which migrates to the shady side, causing increased growth. –Auxin is produced in the shoot tips –Roots are either insensitive to light or show negative phototropism Phototropism short clip:..\..\Biology\Biology Clipart Movies Animations Sounds\Biology movies\phototrop1.2[1].mov..\..\Biology\Biology Clipart Movies Animations Sounds\Biology movies\phototrop1.2[1].mov

Chapter 26 Control of Plant Growth Responses 26.2 Plant Responses Mills AP Bio 2003/2013 Gravitropism –Roots show positive gravitropism If root cap removed, root doesn’t respond to gravity Statoliths in cap –Stems show negative gravitropism –Auxin moves to lower side of stem or root in response to gravity ( may be newer theories) Auxin inhibits growth of root cells on lower side  root grows down Stimulates growth of stem cells on lower side  stem grows up Gravitropism(negative) in stems movie. Time lapse/actual time 1 hour:..\..\Biology\Biology Clipart Movies Animations Sounds\Biology movies\gravitropism.mov..\..\Biology\Biology Clipart Movies Animations Sounds\Biology movies\gravitropism.mov Section of pea root, showing statoliths settled at bottom of cells

Mills AP Bio 2003/2013 Thigmotropism –Unequal growth due to contact with a solid object –Cells opposite the side being touched elongate –Hormones auxin and ethylene may be involved. Thigmotropism movie – Pictures taken at 10 min intervals– morning glory vine grows:..\..\Biology\Biology Clipart Movies Animations Sounds\Biology movies\Thigmotropism vine winding.mov..\..\Biology\Biology Clipart Movies Animations Sounds\Biology movies\Thigmotropism vine winding.mov Chapter 26 Control of Plant Growth Responses 26.2 Plant Responses

Mills AP Bio 2003/2013 Nastic Movements –Independent of direction of stimulus –Types Seismonastic movements –Respond to touch, shaking or thermal »Ex: Mimosa – sleeping grass, Venus flytrap Sleep movements –Occur daily in response to light and dark changes »Ex: Prayer plant – folds up at night –Rhythmic sleep behavior = Circadian rhythms –Circadian rhythms can persist even without the stimulus d/t biological clocks Mimosa plant after being touched..\..\Biology\Biology Clipart Movies Animations Sounds\Biology movies\nastic sensitive_plant_open[2].avi

Mills AP Bio 2003/2013 Greenhouse-grown plants were placed in continuous light. The diurnal opening/closing of the leaflets (nyctinasty) is clearly observed. –Nastic movement over time moviemovie –Also (nyctnasty in silk plant) –From Chapter 26 Control of Plant Growth Responses 26.2 Plant Responses

Mills AP Bio 2003/2013 Nastic Movements-how they work –Stimulus causes K ions to move out of a specialized area of cells (pulvinus) at base of leaf. –Water follows by osmosis  decreased turgor pressure. –Stimulus on one leaf can cause other leaves to close, so must have some system of communication. Venus Flytrap movies:..\..\Biology\Biology Clipart Movies Animations Sounds\Biology movies\venus flytrap movie.mov..\..\Biology\Biology Clipart Movies Animations Sounds\Biology movies\venus flytrap movie.mov..\..\Biology\Biology Clipart Movies Animations Sounds\Biology movies\Venus Fly Trap.wmv..\..\Biology\Biology Clipart Movies Animations Sounds\Biology movies\Venus flytrap eating a spider.wmv Three sensitive trigger hairs on each leaflet Trigger Hairs

Mills AP Bio 2003/2013

Photoperiodism –Physiological responses brought about by changes in the length of day or night. Three plant groups –Short-day plants Flower when the day length is shorter than a critical length. –Long-day plants Flower when the day length is longer than a critical length. –Day-neutral plants Flowering not dependent on day length. –Plant flowering actually depends on a critical length of darkness. –Short days correspond with long nights. Kolonchoe – short day plant Chapter 26 Control of Plant Growth Responses 26.2 Plant Responses

Mills AP Bio 2003/2013 If light at least critical length or shorter  flowers More accurate: If dark at least critical length or longer (regardless of length of light) and continuous  flowers flash of light during dark will inhibit flowering If light at least critical length or longer  flowers More accurate: If dark at least critical length or shorter (regardless of length of light)  flowers If critical darkness longer than critical length, but interrupted by a flash of light, flowering will occur.

Mills AP Bio 2003/2013 Phytochromes –Theory: pigment molecules that detect photoperiods, and directs flowering of plants –Blue green leaf pigments that exist in two forms: P r – phytochrome red (inactive form) – absorbs red light 660mm wavelength – gets converted to P fr P fr – phytochrome far red (active form) – absorbs red light 730nm – gets converted to P r –Sunlight has more red than far red wavelengths, shade and sunset have more far red wavelengths So in sunlight, Pr absorbs red light and gets converted to Pfr, which is the active form and induces flowering etc. –Phytochrome conversion may be the first step in reception  transduction  reaction pathway? Chapter 26 Control of Plant Growth Responses 26.2 Plant Responses

Phytochrome Animation Mills AP Bio 2003/2013

Phytochromes – other functions –P r  P fr (in sunlight) Promotes seed germination, leaf expansion, stem branching, and inhibits stem elongation –Presence of P fr tells some seeds that conditions are right for germination Some seeds need dark to germinate, some do better with some light –In presense of more far red (shade), P fr increases, leading to shade avoidance strategies – stem elongation, flowering to produce seeds Chapter 26 Control of Plant Growth Responses 26.2 Plant Responses

Mills AP Bio 2003/2013 The End