* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Bio3460-22 Hormones
Survey
Document related concepts
G protein–coupled receptor wikipedia , lookup
Magnesium transporter wikipedia , lookup
Cell growth wikipedia , lookup
Cell culture wikipedia , lookup
Hedgehog signaling pathway wikipedia , lookup
Organ-on-a-chip wikipedia , lookup
Cytokinesis wikipedia , lookup
Tissue engineering wikipedia , lookup
Extracellular matrix wikipedia , lookup
Cellular differentiation wikipedia , lookup
List of types of proteins wikipedia , lookup
Biochemical cascade wikipedia , lookup
Transcript
Major Plant Hormones • Auxin (IAA) • Cytokinin (Kinetin, Zeatin) • Gibberellin • Ethylene • Abscisic Acid (ABA) Hormones: • chemical signal produced in one part of the organism & transported to other parts where it binds to a specific receptor and initiates a response (signal transduction) • small amounts can induce a substantial change in growth and development (signal amplified) • small molecules required for easy passage across cell walls Phototropism: A grass seedling growing toward a candle’s light Hormones: • plant hormones can have multiple effects • relative concentration of two or more hormones often control the growth and development of cells Early experiments of phototropism Coleoptile = a modified en-sheathing leaf. It protects primary leaves as seedling grows through soil. 1 Frits Went’s experiments: Discovery of Auxin Auxin is from Greek auxein, “to increase” or “to grow” Auxin Transport: • most Auxin movement is too slow for phloem transport • Auxin normally moves from shoot tip to base NOT in reverse direction • Unidirectional transport is called Polar Transport (one cell to next cell) • Polar transport requires ATP Polar auxin transport: a chemiosmotic model (Layer 1) 2 Polar auxin transport: a chemiosmotic model (Layer 2) Asymmetric location of PIN proteins Normal Polar auxin transport: a chemiosmotic model (Layer 3) To modify localization of PIN proteins Treatment Main function of Auxin is to: • Stimulate the elongation of developing shoot cells Role of Auxin in Cell Elongation Acid Growth Hypothesis Cell elongation in response to auxin: the acid growth hypothesis AUXIN and the statolith hypothesis for root gravitropism Statoliths are starch storing plastids that serve as gravity sensors 3 Auxin – can stimulate or inhibit cell elongation depending on concentration Statoliths are starch storing plastids that serve as gravity sensors Other Uses of Auxins • used commercially in vegetative propagation of plants by cuttings • treat a detached leaf or stem with rooting powder containing Auxin results in the formation of adventitious roots Other Uses of Auxins • used commercially in vegetative propagation of plants by cuttings • treat a detached leaf or stem with rooting powder containing Auxin results in the formation of adventitious roots Extreme proliferation of roots in an Arabidopsis mutant that produces 17-fold higher Auxin conc. Auxin promotes the development of adventitious roots 4 Synthetic Auxins Other Uses of Auxins • 2,4-D is a synthetic Auxin that kills dicot weeds • synthetic Auxins sprayed on Tomato vines induce fruit development without pollination (seedless tomatoes) Cytokinin Was discovered during trial and error attempts to find chemical additives to enhance growth and development of cells in Tissue Culture • liquid endosperm from coconut • degraded samples of DNA active ingredient was modified form of adenine Effects of Cytokinin Kinetin is a heat-induced degradation product of DNA (adenine base) Naturally occurring cytokinin first found in Corn (Zea mays), is the most prevalent cytokinin in higher plants. 1) control of cell division and differentiation (tissue culture) 2) apical dominance Naturally occurring cytokinin in other plants Named Cytokinins because they stimulate cell division or cytokinesis 5 Effects of Cytokinin 1) control of cell division and differentiation • when stem tissue is cultivated without cytokinin cells grow very large but do not divide • adding cytokinins alone has no effect • cytokinins along with auxin control cell division and differentiation in tissue culture Effects of Cytokinins 2) Apical dominance • Auxin and Cytokinin have counteracting effects on apical dominance IAA is a natural Auxin Kinetin is an artificial Cytokinin • plants that over produce cytokinins tend to have “bushier” growth - more than one main stem Apical dominance: with apical bud (left), apical bud removed (right) 6 “Foolish seedling disease” in rice Gibberellins • first discovered as a chemical produced by a fungus (Gibberella fujikuroi) • fungus was the cause of “foolish seedling disease” • infected seedlings grew tall & spindly - they toppled over before they could mature and flower Three of the more than 110 Gibberellins Gibberellin Effects 1) Stem Elongation 2) Fruit growth (grapes) 3) Seed germination Gibberellin Effects Gibberellin Mutants 1) Stem Elongation • stimulate growth in leaves and stems • stimulate cell elongation and cell division 7 Figure 20.5 The three stages of GA biosynthesis Non-13-Hydroxylation pathway occurs in some crop plants and Arabidopsis plants 13-Hydroxylation pathway is the major pathway in many plants This pathway results in the synthesis of bioactive GA1 We will focus on this pathway Figure 20.7 Portion of GA biosynthetic pathway showing mutation-blocked metabolic steps GA1 is active form --> Figure 20.7 Portion of GA biosynthetic pathway showing mutation-blocked metabolic steps Figure 20.9 Phenotypes and genotypes of peas that differ in GA 1 content of their vegetative tissue Treating pea dwarfism with a growth hormone (GA1) 8 Figure 20.10 Genetically engineered dwarf wheat plants GA1 is active form --> Figure 20.7 Portion of GA biosynthetic pathway showing mutation-blocked metabolic steps DELLA Protein Components: GA Signal Transduction Pathway: • GID1 hormone receptor binds GA • After binding, GA-GID1 interacts with DELLA protein and results in the degradation of the DELLA protein • DELLA protein is a NEGATIVE regulator of plant growth - stem elongation • GA binding then removes a restriction on growth • DELLA Domain – regulatory domain – GA binding • GRAS Domain – functional domain prevents gene expression controlling stem elongation Effect of Mutations in: • DELLA Domain > makes dwarf plants & GA insensitive • GRAS Domain > makes tall plants & will NOT exhibit reduced growth even if GA biosynthesis is stopped Figure 20.14 Structure of the GA-GID1a-DELLA complex Part of the Gibberellin Biosynthesis Pathway and Signal Transduction Pathway GA8 GA2ox sln 9 Figure 20.16 Domain structures of the RGA and GAI repressor proteins Figure 20.15 DELLA-domain (N-terminal end of protein - the first 5 amino acids are: Aspartic Acid (D), Glutamic Acid (E), Leucine (L), Leucine (L), Alanine (A) Figure 20.19 Degradation of the DELLA protein Figure 20.15 DELLA-domain (N-terminal end of protein - the first 5 amino acids are: Aspartic Acid (D), Glutamic Acid (E), Leucine (L), Leucine (L), Alanine (A) GA1 receptor -A mutation in this receptor will result in dwarf plants even when GA levels are high Part of the Gibberellin Biosynthesis Pathway and Signal Transduction Pathway GA8 GA2ox sln Other Effects of Gibberellin 2) Fruit growth • commercial application to “Thompson” seedless grapes produces larger grapes • internodes of grape stem elongates and provides more air circulation and less yeast and other microbe pest growth 10 The effect of gibberellin treatment on seedless grapes Figure 20.4 Gibberellin induces growth in “Thompson Seedless” grapes Other Effects of Gibberellin 3) Seed germination • developing embryos produce GA • GA stimulates synthesis of a amylase (a digestive enzyme) that mobilizes stored nutrients (breaks down starch) Ethylene (H2C=CH2) Ethylene (H2C=CH2) • has numerous effects on plants - many effects that were previously ascribed to other hormones (particularly Auxin) • gas formed from plant biosynthetic pathways Physiological Effects (Amino Acid) 1) Fruit ripening 2) Triple response to mechanical stress 3) Flooding induced aerenchyma production 4) Leaf abscission & programmed cell death 11 Ethylene Triple Response to Mechanical Stress Physiological Effects • reduced stem elongation • thickening of stem • horizontal growth 1) Fruit ripening (Bananas, Tomatoes) • Ethylene causes production of enzymes (Cellulase & Pectinase) that breakdown cellulose and pectin - structural components of cell walls • Ethylene causes starches to be converted to sugar Ethylene induces the triple response in pea seedlings Ethylene signal-transduction mutants can be distinguished by their different responses to experimental treatments Ethylene triple response in mutants: ein mutant (left), ctr mutant (right) A developmental response of corn roots to flooding and oxygen deprivation involves ethylene 12 Abscission of a maple leaf Abscisic Acid (ABA) Physiological Effects 1) Stomatal Closure 13 Fig. 1 Contrasting stomatal responses to exogenous ABA applied to diverse lineages of vascular plants. T J Brodribb, S A M McAdam Science 2011;331:582-585 14