BIO 1150 1st Edition Lecture 26Topic Discussed: Plant Signaling and HormonesSignal transduction pathways link signal reception to response- Receptors-detect changes in their environment- For stimulus to elicit a response, certain cells must have an appropriate receptor- Stimulation of the receptor initiates a specific signal transduction pathwayReception- Internal and external signals are detected by receptors, proteins that change in response tospecific stimuliTransductionSecond messengers- transfer/amplify signals from receptors to proteins that cause responsesDe-Etiolated-stopped branching, green, has reached lightEtiolated plant- stemming out to reach lightPlant Signaling works by three main steps: reception, transduction and responsePlant Hormones help coordinate growth, development and responsesHormones- chemical signals that coordinate different parts of an organismPhototropism- growth response to light, responsive to direction of lightLed to discovery of first plant hormoneFritizs Went- grandfather of plant hormonesThese 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.Chemical that diffused into stem, causes cell elongation (auxin)Plant Hormones- Hormones- control plant growth/development by affecting the division, elongation, and differentiation of cells- Plant hormones- made in very low concentration, but a minute amount can greatly affect growth and development of a plant organ- They usually act some distance away from where they are producedAuxin-cell elongation- acid growth hypothesis- auxin stimulates proton pumps in the plasma membrane- proton pumps- lower the pH in the cell wall, which activates expansins (enzymes) which loosens the cell wall- With loose cellulose, the cell can elongateLateral and Adventitious Root Formation- Auxin - root formation and branching- Overdose- can kill dicotsCytokinins- cell division- produced in actively growing tissues such as roots, embryos, and fruits- works with auxin to control cell division and differentiation- Juvenility- “keeps young”Control of Apical Dominance- Cytokinins balance auxin and other factors to control of apical dominance- Apical dominance- a terminal bud’s ability to suppress development of axillary buds- terminal bud removal- plants become bushierGibberellins - stem elongation, fruit growth, and seed germinationFruit Growth- auxin and gibberellins needed for fruit to set- Gibberellins are used for seedless grapesAbscisic acid (ABA) -slows growth- Seed dormancy- Drought tolerance- Stimulates guard cells to close stomataSeed Dormancy- Makes sure that the seed will germinate only in optimal conditions- ABA can be broken down by heavy rain, light, or prolonged cold- If ABA isn’t effective precautious germination can happen- Precocious germination – germinates too earlyEthylene- A response to stress: drought, flooding, mechanical pressure, injury, and infection- Effects include: response to mechanical stress, senescence, leaf abscission, and fruit ripeningThe Triple Response- causes stem to bendStem elongation slows downSeedling curvesThickenHelps to circumvent obstacles- Ethylene-insensitive mutants fail to undergo the triple response after exposure to ethylene- Some mutants don’t respond to ethylene synthesis inhibitors- ein – ethylene insensitive- ctr – constituent triple responseSenescence -programmed death of plant cells or organs- apoptosis- the programmed destruction of cells, organs, or whole plants- A burst of ethylene is associated with this- Fruit ripening is also stimulated by ethyleneLeaf Abscission- A change in the balance of auxin and ethylene Lets leaves fall off in the
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