BIOL 152 1st Edition Lecture 13 Outline of Last Lecture I Reproduction in gymnosperms and angiosperms a Homologous structures b Similarities and differences c Flowering plant apomorphies II How apical meristems work a Indeterminate growth b Tunica and corpus layers c Maturation of cells and tissues III Origin of flowers a Change to determinate growth b Control of call fates i Position effects ii Genetic influence 1 ABC model of flower genetics IV Plants respond to light a Discovery of plant hormones i Auxin 1 Charles and Francis Darwin 2 Boysen Jensen and Fritz Went ii Produced by stem tip iii Influences plant growth Outline of Current Lecture I Plants respond to light a Discovery of plant hormones i Auxin first one discovered 1 Named by Fritz Went 2 Produced by stem tip 3 Influences plant growth II Other plant hormones a Cytokinin i Stimulates cell division b Gibberellin i Stimulates germination ii Promotes fruit growth c Abscisic Acid These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute III i Induces dormancy d Ethylene i Causes senescence ripening Other tropisms a Gravitropism b Thigmotropism Plant Defense Outline I II III Advantages and disadvantages of a plant s defenses Pathogens a Mode of entry b Types of pathogens Plant immune responses basal and specific a Hypersensitive response b Acquired resistance Current Lecture Conclusions from experiments Darwin and Boysen Jenson Phototropism controlled by stem tip Exposure of tip to light necessary Lower stem region does not control tip response Response mediated by diffusible substance Substance produced by stem tip Fritz W Went Created climatron o Dome like structure that gave the ability to demonstrate plant diversity Experiment Removed tip from shoot and placed it on agar block Substance diffuses into block also had a control no growth Agar block with substance grew offset block showed curvature Conclusions Substance produced by tip Substance in agar transferred to stem Substance stimulates elongation Transported from tip to base o Polar transport via PIN proteins fig 31 9 Went named substance Auxin First plant hormone isolated Why is polar transport a critical element of auxin function Phototropism requires cell expansion on only one side of the stem Further auxin discoveries Structure Kenneth Thimann 1904 97 Transport requires ATP Auxin loosens cell wall o Changes molecular structure of cellulose o Cells elongate turgor pressure Photoreception yellow pigment related to riboflavin o May control auxin activity Other auxin effects Promotes fruit growth o Seedless tomatoes 2 4 D synthetic auxin o Disrupts plant growth o Some plants more sensitive than others Broad leaf weeds Other plant hormones Cytokinin enhances cell growth and division Modified form of adenine o Carlos Miller 1923 2012 o Produced by roots Stimulate cell divsions Partner with auxin to control plant growth Apical dominance auxin and cytokinin are ANTAGONISTS Auxin from stem tip suppresses axillary bud growth Stem tip removal cytokinin from roots stimulates axillary buds Top of tree auxin levels high cytokinin levels low Bottom of tree auxin levels low cytokinin levels high Hormones generate plant symmetry Gibberellins Discovered in Japan o Named for fungus o Causes foolish seedling disease Elongates plants o Parter with auxin Stimulates seed germination Promotes fruit growth 100 gibberellins isolated Abscisic Acid Slows growth Induces dormancy Stomata closure in plants under stress Not involved with leaf abscission o Hormone misnamed Ethylene A gas Causes senescence Fruit ripening o One bad apple Leaf abscission o Interaction with auxin o Special layers of cells o Separates leaf protects stem Other tropisms Gravitropism Shoots go up stems go down Statholiths starch grains o Active transport of auxin o Auxin medicated BUT mutant starchless plants o Respond slightly without statholiths Thigmotropism Response to touch Vine tendrils o Cling to surface Rapid leaf movements Plant Defense Advantages Disadvantages Poison Inability to move Mechanical defense thorns etc Weather dependent Regeneration Pollinator dependent Isolate disease Speed of response Autotrophic Cell walls protection How might pathogens enter a plant Entry for pathogens STOMATA Types of pathogens Biotrophic eating live material viral bacterial fungal Necrotropic eating dead material bacterial fungal Different responses to different attackers Immune systems They can be both broad and specific Can isolate specific portions of infection to contain and rid Can send chemical signals to uninfected areas to resist possible infection Immune system Basil receptors are on plasma membrane Immune system Specific receptors inside cell Refer to fig 32 4 HOW TO STOP BIOTROPIC PATHOGEN Close stomata Plug xylem Produce antimicrobial compounds Hypersensitive response
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