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50 Cards in this Set
- Front
- Back
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seed
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contains early embryo; may be in “suspended animation”
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dormant seed
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development is stopped even when external conditions are adequate for growth; ensures survival during unfav. conditions, results in germination when conditions fav.
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mechanisms that maintain dormancy
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exclusion of H2O or oxygen from embryo by seed coat; mechanical restraint of embryo by tough seed coat; chemical inhibition of germination
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germinate
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sprout (dormancy broken)
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steps of germination
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imbibition (hydration, seed takes up water); metabolic changes - enzymes activated, RNA & proteins synthesized, rate of cell. resp. increases, other pathways activated; chemical building blocks accessed; by hydrolyzing starch, proteins & lipids stored in seed; radicle emerges as seedling
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cotyledon
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“seed leaves”
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endosperm
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specialized triploid seed tissue found only in angiosperms; surrounds embryo
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radicle
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embryonic plant root
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seedling
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when radicle emerges from seed coat
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angiosperm
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flowering seed plants (monocots and eudicots)
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monocot
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angiosperm with single embryonic cotyledon; growing shoot protected by coleptile
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eudicot
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angiosperm with two embryonic cotyledons that protect growing shoot
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coleoptile
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cylindrical sheath of cells protecting growing shoot of monocots
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plant hormones
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chemical signals that act at very low concentrations at sites often distant from where they are produced; each plant hormone plays multiple regulatory roles; complex interactions
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photoreceptors
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pigments assoc. with proteins; light acts directly on photoreceptors, which then regulate developmental processes that need to be responsive to light
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genetic screen
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creating a large collection of randomly mutated plants & identifying those individuals that are likely to have a defect in pathway of interest
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genetic screen method
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1) randomly mutate plant genes via transposon or chemical mutagens; 2) grow treated plants and examine for specific phenotype; once mutant place selected compare genotypes with wild-type plants
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gibberellin functions
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promotes seed germination (inc. mobilization of seed reserves), stem growth, fruit development, breaks winter dormancy, mobilizes nutrient reserves in grass seeds
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auxin functions
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related to phototropism; promotes stem elongation, lateral root initiation and fruit dev.; inhibits axillary bud outgrowth (by helping to maintain apical dominance), leaf abscission and root elongation
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abscisic acid functions
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maintains seed dormancy; closes stomata
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brassinosteroids functions
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promote stem and pollen tube elongation, promotes vascular tissue differentiation; receptor is an integral membrane protein rather than cytoplasmic receptor
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cytokinins functions
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required for continuous cell division; most are derivatives of adenine (150 kinds isolated); inhibit leaf senescence; promote cell division and axillary bud outgrowth; affect root growth
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ethylene functions
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promotes fruit ripening and leaf abscission; inhibits stem elongation; causes an increase in its own production; diffuses readily throughout fruit and to others; silver salts inhibit its action; maintains apical hook via asymmetrical production of ethylene
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aleurone layer
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gibberellins diffuse through endosperm to this layer underneath the seed coat, cascade occurs in the aleurone layer, enzymes synthesized and secreted to digest proteins and starch stored in endosperm
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phototropism
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plant stems bend toward light source (auxin!)
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auxin, general
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made in shoot apex. diffuses down shoot in a polar (unidirectional) fashion, stimulating cell elong. also works in a leaf petiole from leaf blade toward stem; in root toward the root tip
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gibberellin, general
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plants produce gibberellic acid; applying it to plants causes growth
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polar transport of auxin
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requires diffusion across plasma mem., membrane protein asymmetry (active transport carriers located in cell membrane at basal end of cell), chemiosmosis removes H+ from cell, inc. intracellular pH and dec. pH in cell wall, sets up electrochem. gradient to provide PE to drive auxin transport
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Ionization of weak acid (Auxin)
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A- + H+ <--> HA (when pH low, increased H+ conc. drives rxn to right, HA predominates. other way around when pH higher and there is more A-)
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Lateral redistribution of auxin
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Responsible for directional plant growth
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Gravitropism
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Auxin moves to lower side of shoot that is tipped sideways, causing more growth on lower side and thus upward bending of shoot (neg. gravitropism = upward gravitropic response of shoots, pos. gravitropism = roots bend downward)
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apical dominance
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the main central stem of the plant is dominant over (i.e., grows more strongly than) other side stems; on a branch the main stem of the branch is further dominant over its own side branchlets.
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parthenocarpy
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fruit development without fertilization
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acid growth hypothesis
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protons pumped from cytoplasm to cell wall, lowers pH of cell wall, activates expansin enzymes that catalyze changes in cell wall structure so that polysaccharaides adhere to e.o. less strongly; cell wall can now stretch as cell expands. Auxin increases syn. of proton pumps and guides insertion into plasma mem.
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excessively tall plants
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hormone syn. always "on" even in absence of hormone. presume normal allele for mutant gene codes for an inhibitor of hormone signal trans. pathway
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dwarf plants
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hormone response always "off". deficient in hormone synthesis and do not respond to added hormone
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Auxin/Gibberellin act similarly at molecular-level
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Mutations leading to either excessively tall or dwarf plants affect same protein, a repressor of a T.F. that stimulates expression of growth-promoting genes. One region binds to transcription complex to inhibit transcription (this is mutant region in excessively tall plants b/c repressor doesn't bind). Other region causes protein to be removed from transc. complex (this is mutant region in dwarf plants b/c repressor always bound to complex)
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F-box
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Region on receptors for both G & A that facilitates protein-protein interactions necessary for protein breakdown (plants have hundreds of these in their genomes)
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Triple response
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Stunted growth occurs when plants treated with ethylene (inhibits stem elong., promotes lateral swelling of stems; decreases stem sensitivity to gravitropic stimulation)
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Apical hook
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Formed at tip of stems of many eudicot seedlings (no coleoptile); protects shoot apex while growing through soil
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Cytokinins & Two-Component System
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Signal transduction pathway normally found in bacteria; cytokinin appears to act thru pathway w/ proteins that have aa seq. similar to two-comp. systems. Receptor acts as protein kinase, phosphorylates itself and the target; target protein, usually a T.F., regulates the response; (see Arabidopsis example p. 550)
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vivipary
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premature germination
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photomorphogenesis
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some physiological and developmental events in plants are controlled by light (respond to light quality & quantity)
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phototropin
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blue-light receptor protein in plasma mem.; flavin mononucleotide absorbs blue light at 436nm; light absorption changes protein shape, exposes active site for protein kinase, initiates signal trans. cascade, stimulates cell elong. by auxin
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zeaxanthin
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blue-light receptor plastid pigment; works w/ phototropin in light-induced opening of stomata
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cryptochromes
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yellow pigments that absorb blue & ultraviolet light; located in plant cell nucleus & affect seedling dev. and flowering. Strong blue light inhibits cell elong. via cryptochrome action
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phytochrome
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Bluish photoreceptor in cytosol of plants; exists in two isoforms, P(r) and P(fr). Cytoplasmic protein composed of two subunits (each consisting of protein chain and a chromophore - a nonprotein pigment); transcription of genes involved in phytochrome responses changes when P(r) converted to P(fr)
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P(r)
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Phytochrome "ground" state, absorbs red light. When photon red light absorbed, converts to P(fr) isoform
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P(fr)
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Phytochrome active form, triggers most biological processes; absorbs far-red light and converts back to P(r)
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Circadian rhythms
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Outward manifestation of biological clock, which can be entrained in plants within limits by light-dark cycles that change
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