BIOL 152 1st Edition Lecture 13 Outline of Last Lecture I. Reproduction in gymnosperms and angiospermsa. Homologous structuresb. Similarities and differencesc. Flowering plant apomorphiesII. How apical meristems worka. Indeterminate growthb. Tunica and corpus layersc. Maturation of cells and tissuesIII. Origin of flowersa. Change to determinate growthb. Control of call fatesi. Position effectsii. Genetic influence1. ABC model of flower geneticsIV. Plants respond to lighta. Discovery of plant hormonesi. Auxin1. Charles and Francis Darwin2. Boysen-Jensen and Fritz Wentii. Produced by stem tipiii. Influences plant growthOutline of Current Lecture I. Plants respond to lighta. Discovery of plant hormonesi. Auxin-first one discovered1. Named by Fritz Went2. Produced by stem tip3. Influences plant growthII. Other plant hormonesa. Cytokinini. Stimulates cell divisionb. Gibberellini. Stimulates germinationii. Promotes fruit growthc. Abscisic AcidThese 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.i. Induces dormancyd. Ethylenei. Causes senescence, ripeningIII. Other tropismsa. Gravitropismb. ThigmotropismPlant Defense Outline:I. Advantages and disadvantages of a plant’s defensesII. Pathogensa. Mode of entryb. Types of pathogensIII. Plant immune responses (basal and specific)a. Hypersensitive responseb. Acquired resistanceCurrent LectureConclusions 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 tipFritz W. Went- Created climatrono Dome-like structure that gave the ability to demonstrate plant diversityExperiment:- 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 curvatureConclusions: - Substance produced by tip- Substance in agar transferred to stem- Substance stimulates elongation- Transported from tip to baseo “Polar transport” via PIN proteins (fig. 31.9)- Went named substance “Auxin”- First plant hormone isolatedWhy 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 wallo Changes molecular structure of celluloseo Cells elongate “turgor pressure”- Photoreception= yellow pigment related to riboflavino May control auxin activityOther auxin effects- Promotes fruit growtho Seedless tomatoes- 2, 4-D synthetic auxino Disrupts plant growtho Some plants more sensitive than others Broad leaf weedsOther plant hormonesCytokinin- enhances cell growth and division- Modified form of adenineo Carlos Miller (1923-2012)o Produced by roots- Stimulate cell divsions- Partner with auxin to control plant growthApical 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 symmetryGibberellins- Discovered in Japano Named for funguso Causes “foolish seedling disease”- Elongates plantso Parter with auxin- Stimulates seed germination- Promotes fruit growth- 100+ gibberellins isolatedAbscisic Acid - Slows growth- Induces dormancy - Stomata closure in plants under stress- Not involved with leaf abscissiono Hormone misnamedEthylene- A gas- Causes senescence- Fruit ripeningo One bad apple…- Leaf abscissiono Interaction with auxino Special layers of cellso Separates leaf, protects stemOther tropismsGravitropism- Shoots go up, stems go down- Statholiths (starch grains)o Active transport of auxino Auxin medicated- BUT, mutant, starchless plantso Respond slightly without statholithsThigmotropism- Response to touch- Vine tendrilso Cling to surface- Rapid leaf movementsPlant DefenseAdvantages DisadvantagesPoison Inability to moveMechanical defense (thorns, etc.) Weather dependentRegeneration Pollinator dependentIsolate disease Speed of responseAutotrophicCell walls (protection)How might pathogens enter a plant?Entry for pathogens:STOMATATypes of pathogens- Biotrophic- eating live material (viral, bacterial, fungal)- Necrotropic- eating dead material (bacterial fungal)- Different responses to different attackersImmune 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 infectionImmune system (Basil)- receptors are on plasma membraneImmune system (Specific)- receptors inside cell(Refer to fig. 32.4)HOW TO STOP BIOTROPIC PATHOGEN:- Close stomata- Plug xylem- Produce antimicrobial compounds- Hypersensitive
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