BIOL 240W 1st Edition Lecture 15Outline of Last Lecture I. Big Picture/ ContextII. ReproductionIII. Life Cycle of PlantsIV. Plant Structure/function and ReproductionV. Asexual ReproductionVI. Selective BreedingVII. Genetically Modified OrganismsOutline of Current Lecture I. Signal TransductionII. Plant HormonesCurrent LectureI. Signal Transductiona. At a molecular level, responses occur based on environmental influences.b. Genes produce proteins that produce enzymes to catalyze a reaction. i. These genes are not always onii. Need a stimulus to cause enzyme to be producedc. Cell gets signal. Information must go into cell, and cell responds by turning genes off or ond. Antagonistic hormones i. Ex: glucagon brings glucose back to normal levels. Negative feedback (this occursin animals)e. The Central Dogmai. DNARNAProteinii. Basis of all biologyf. Plants are Stationary, so they cannot move away from a bad stimulus. If they encounter something bad, they must alter growth and development by picking up a signalg. Plants also have indeterminate growth. Meristems can produce growth if it is neededh. ReceptionTransductionResponse is the basis for signal transductioni. Plants contain receptors embedded into the cell membrane. i. Hormone or environmental stimulus binds to receptor. 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.ii. Once binding occurs, proteins are relayed from receptor sites to (most likely) thenucleus. iii. This activates cellular responsesj. Receptioni. Plant receives internal or external signalii. Protein receptors spanning across cell membrane are ready to receive information (first messenger)k. Transductioni. Second messengers take information from initial receptor and relay it to the nucleusl. Responsei. In most cases, genes are turned on. This increases the activity of enzymesii. Regulation occurs at transcriptional or translational levelII. Plant Hormonesa. Hormones coordinate growth, development, and responses to stimuli (chemical signals)b. Can operate at very low concentrationsc. Major plant hormonesi. Tropism- once response is received, curvature of organs occurs to move plant toward or away from stimulus1. Ex- phototropism- coleoptile of single grass shoot will bend toward light.Certain cells expand on certain sides of the plant that allows it to bend toward lighta. Charles Darwin did an experiment on this. When the tip of the shoot was removed, the plant did not display phototropismb. Found there was something happening at the tip of the plant that caused it to bendc. Boysen Jenson found the messenger was water solubled. Went discovered the distribution of a mobile, growth-promotingsubstance caused phototropismd. Auxin- any chemical promoting elongation of coleoptilesi. Indolacetic acid is a common auxin derived from tryptophanii. Auxin is pumped downwardiii. Acid-growth hypothesis- using ATP, protons are pumped from one side of membrane to another. This reduces pH, so acidic space-containing expansin cellsloosen cross-links in the cell wall. The cellulose is loosened, and now the cell canelongate. Turgor pressure expands the celliv. In class video- plant responds preferentially to blue light instead of red (curves toward blue light) because light wavelengths below 500nm induce curvature in plants. Do not respond to green light, for example, because plants reflect green lightv. Auxin inhibits axillary buds. Enforces apical dominance. The herbicide 2,4-dichlorophenoxyacetic acid succumbs eudicots to overgrowth due to hormone overdose (monocots not affected)e. Cytokininsi. Stimulate cell division (cytokinesis)ii. Exist in roots. Are transported in xylem and act with auxin to stimulate growth by division and expansion of cells. Also stimulate growth of lateral budsiii. Isolated parenchyma cells exposed to:1. Auxin- cell expansion2. Cytokinins- no response3. Auxin + cytokinin: expand and divideiv. Ratio of these two stimuli controls differentiationv. Play an important role in the control of apical dominance1. Auxin inhibits growth of axillary buds2. Cyotokinins promote growthf. Gibberellins i. Variety of effectsii. Discovered from fungal pathogen of riceiii. Produced in apical buds, roots, and young leavesiv. Promote stem elongation by elongation of cells and cell divisionsv. Dwarf varieties of plants are gibberellin deficient (mutation in gene that encodesgibberellin biosynthesis enzyme)vi. Adding gibberellins promotes premature flowering before harvesting. However, these stimuli are used in fruit production1. Auxin and gibberellins must be present for fruit to developvii. Play a role in germination. Produced by embryos upon imbibition and stimulate production of enzymes that digest complex carbs to simple sugars and aid in seedling growthg. Abscisic Acidi. Don’t directly contribute to leaf abscission (falling)ii. Slows growth and counteracts effects of other plant hormones1. Critical processes include seed dormancy and drought tolerance2. Seed dormancy- dormancy is broken when ABA is removed by heavy rain, light, or prolonged cold. Early germination occurs by inactive or lowlevels of ABA. ABA levels increase during seed maturation. ANTAGONISTIC3. Drought Tolerance- Plants in dry areas need control of closing and opening of stomata. If ABA increases, stomata close (drought tolerance) because if causes K+ channels to openh. Ethylene- triple response to mechanical stressi. Elongation of stem, thickening of stem, horizontal growth1. If plant is bumping into something, it must get around it from triple response to this mechanical
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