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Pathogens • Agrobacterium tumefaciens • Agrobacterium rhizogenes • Pseudomonas syringeae • Pseudomonas aeruginosa • Viroids • DNA viruses • RNA viruses • Fungi • oomycetes • nematodes Symbionts • N-fixers • Endomycorrhizae • Ectomycorrhizae Plant Growth Decide which way to divide & which way to elongate • Periclinal = perpendicular to surface: get longer • Anticlinal = parallel to surface: add more layers Now must decide which way to elongate: which walls to stretch Plant Cell Walls and Growth Carbohydrate barrier surrounding cell • Protects & gives cell shape • 1˚ wall made first • mainly cellulose • Can stretch! • 2˚ wall made after growth stops • Lignins make it tough Plant Cell Walls and Growth • 1˚ wall made first • mainly cellulose • Can stretch! Control elongation by controlling orientation of cell wall fibers as wall is made • 1˚ walls = 25% cellulose, 25% hemicellulose, 35% pectin, 5% protein (but highly variable) Plant Cell Walls and Growth 1˚ walls = 25% cellulose, 25% hemicellulose, 35% pectin, 5% protein (but highly variable) Cellulose: ordered chains made of glucose linked b 1-4 • Cross-link with neighbors to form strong, stable fibers Plant Cell Walls and Growth Cellulose: ordered chains made of glucose linked b 1-4 • Cross-link with neighbors to form strong, stable fibers • Made by enzyme embedded in the plasma membrane Plant Cell Walls and Growth Cellulose: ordered chains made of glucose linked b 1-4 • Cross-link with neighbors to form strong, stable fibers • Made by enzyme embedded in the plasma membrane • Guided by cytoskeleton Plant Cell Walls and Growth Cellulose: ordered chains made of glucose linked b 1-4 • Cross-link with neighbors to form strong, stable fibers • Made by enzyme embedded in the plasma membrane • Guided by cytoskeleton • Cells with poisoned µtubules are misshapen Plant Cell Walls and Growth Cellulose: ordered chains made of glucose linked b 1-4 • Cross-link with neighbors to form strong, stable fibers • Made by enzyme embedded in the plasma membrane • Guided by cytoskeleton • Cells with poisoned µtubules are misshapen • Other wall chemicals are made in Golgi & secreted Plant Cell Walls and Growth Cellulose: ordered chains made of glucose linked b 1-4 • Cross-link with neighbors to form strong, stable fibers • Made by enzyme embedded in the plasma membrane • Guided by cytoskeleton • Cells with poisoned µtubules are misshapen • Other wall chemicals are made in Golgi & secreted • Only cellulose pattern is tightly controlled Plant Cell Walls and Growth Cellulose pattern is tightly controlled • 6 CES enzymes form a “rosette”: each makes 6 chains -> 36/fiber Plant Cell Walls and Growth Cellulose pattern is tightly controlled • 6 CES enzymes form a “rosette”: each makes 6 chains -> 36/fiber • Rosettes are guided by microtubules Plant Cell Walls and Growth Cellulose pattern is tightly controlled • 6 CES enzymes form a “rosette”: each makes 6 chains • Rosettes are guided by microtubules • Deposition pattern determines direction of elongation Plant Cell Walls and Growth Cellulose pattern is tightly controlled • Deposition pattern determines direction of elongation • New fibers are perpendicular to growth direction, yet fibers form a mesh Plant Cell Walls and Growth New fibers are perpendicular to growth direction, yet fibers form a mesh Multinet hypothesis: fibers reorient as cell elongates Old fibers are anchored so gradually shift as cell grows Plant Cell Walls and Growth New fibers are perpendicular to growth direction, yet fibers form a mesh Multinet hypothesis: fibers reorient as cell elongates Old fibers are anchored so gradually shift as cell grows Result = mesh Plant Cell Walls and Growth 1˚ walls = 25% cellulose, 25% hemicellulose, 35% pectin, 5% protein (but highly variable) Hemicelluloses AKA cross-linking glycans: bind cellulose Plant Cell Walls and Growth Hemicelluloses AKA cross-linking glycans: bind cellulose Coat cellulose & bind neighbor Plant Cell Walls and Growth Hemicelluloses AKA cross-linking glycans Coat cellulose & bind neighbor Diverse group of glucans: also linked b 1-4, but may have other sugars and components attached to C6 Hemicelluloses Diverse group of glucans: also linked b 1-4, but may have other sugars and components attached to C6 makes digestion more difficult Hemicelluloses Diverse group of glucans: also linked b 1-4, but may have other sugars and components attached to C6 makes digestion more difficult Assembled in Golgi Plant Cell Walls and Growth Hemicelluloses AKA cross-linking glycans A diverse group of glucans also linked b 1-4, but may have other sugars and components attached to C6 makes digestion more difficult Assembled in Golgi Secreted cf woven Plant Cell Walls and Growth 1˚ walls = 25% cellulose, 25% hemicellulose, 35% pectin, 5% protein (but highly variable) Pectins: fill space between cellulose-hemicellulose fibers Pectins Pectins: fill space between cellulose-hemicellulose fibers Form gel that determines cell wall porosity(& makes jam) Pectins Pectins: fill space between cellulose-hemicellulose fibers Form gel that determines cell wall porosity (& makes jam) Acidic, so also modulate pH & bind polars Pectins Pectins: fill space between cellulose-hemicellulose fibers Form gel that determines cell wall porosity (& makes jam) Acidic, so also modulate pH & bind polars Backbone is 1-4 linked galacturonic acid Pectins Backbone is 1-4 linked galacturonic acid Have complex sugar side-chains, vary by spp. Pectins Backbone is 1-4 linked galacturonic acid Have complex sugar side-chains, vary by spp. Plant Cell Walls and Growth Also 4 main multigenic families of structural proteins Plant Cell Walls and Growth Also 4 main multigenic families of structural proteins Amounts vary between cell types & conditions Plant Cell Walls and Growth Also 4 main multigenic families of structural proteins Amounts vary between cell types & conditions 1. HRGP: hydroxyproline-rich glycoproteins (eg extensin) • Proline changed to hydroxyproline in Golgi Plant Cell Wall Proteins 1. HRGP: hydroxyproline-rich glycoproteins (eg extensin) • Proline changed to hydroxyproline in Golgi • Highly glycosylated: helps bind CH2O 1. • • • Plant Cell Wall Proteins HRGP: hydroxyproline-rich glycoproteins (eg extensin) Proline changed to hydroxyproline in Golgi Highly glycosylated: helps bind CH2O Common in cambium, phloem 1. • • • • Plant Cell Wall Proteins HRGP: hydroxyproline-rich glycoproteins (eg extensin) Proline changed to hydroxyproline in Golgi Highly glycosylated: helps bind CH2O Common in cambium, phloem Help lock the wall after growth ceases Plant Cell Wall Proteins 1. HRGP: hydroxyproline-rich glycoproteins (eg extensin) • Proline changed to hydroxyproline in Golgi • Highly glycosylated: helps bind CH2O • Common in cambium, phloem • Help lock the wall after growth ceases • Induced by wounding 2. PRP: proline-rich proteins Plant Cell Wall Proteins 1. HRGP: hydroxyproline-rich glycoproteins (eg extensin) 2. PRP: proline-rich proteins • Low glycosylation = little interaction with CH2O 1. 2. • • Plant Cell Wall Proteins HRGP: hydroxyproline-rich glycoproteins (eg extensin) PRP: proline-rich proteins Low glycosylation = little interaction with CH2O Common in xylem, fibers, cortex 1. 2. • • • Plant Cell Wall Proteins HRGP: hydroxyproline-rich glycoproteins (eg extensin) PRP: proline-rich proteins Low glycosylation = little interaction with CH2O Common in xylem, fibers, cortex May help lock HRGPs together 1. 2. • • • 3. • Plant Cell Wall Proteins HRGP: hydroxyproline-rich glycoproteins (eg extensin) PRP: proline-rich proteins Low glycosylation = little interaction with CH2O Common in xylem, fibers, cortex May help lock HRGPs together GRP: Glycine-rich proteins No glycosylation = little interaction with CH2O 1. 2. • • • 3. • • Plant Cell Wall Proteins HRGP: hydroxyproline-rich glycoproteins (eg extensin) PRP: proline-rich proteins Low glycosylation = little interaction with CH2O Common in xylem, fibers, cortex May help lock HRGPs together GRP: Glycine-rich proteins No glycosylation = little interaction with CH2O Common in xylem 1. 2. • • • 3. • • • Plant Cell Wall Proteins HRGP: hydroxyproline-rich glycoproteins (eg extensin) PRP: proline-rich proteins Low glycosylation = little interaction with CH2O Common in xylem, fibers, cortex May help lock HRGPs together GRP: Glycine-rich proteins No glycosylation = little interaction with CH2O Common in xylem May help lock HRGPs & PRPs together Plant Cell Wall Proteins 1. HRGP: hydroxyproline-rich glycoproteins (eg extensin) 2. PRP: proline-rich proteins 3. GRP: Glycine-rich proteins • No glycosylation = little interaction with CH2O • Common in xylem • May help lock HRGPs & PRPs together 4. Arabinogalactan proteins Plant Cell Wall Proteins 1. HRGP: hydroxyproline-rich glycoproteins (eg extensin) 2. PRP: proline-rich proteins 3. GRP: Glycine-rich proteins 4. Arabinogalactan proteins • Highly glycosylated: helps bind CH2O Plant Cell Wall Proteins 1. HRGP: hydroxyproline-rich glycoproteins (eg extensin) 2. PRP: proline-rich proteins 3. GRP: Glycine-rich proteins 4. Arabinogalactan proteins • Highly glycosylated: helps bind CH2O • Anchored to PM by GPI Plant Cell Wall Proteins 1. HRGP: hydroxyproline-rich glycoproteins (eg extensin) 2. PRP: proline-rich proteins 3. GRP: Glycine-rich proteins 4. Arabinogalactan proteins • Highly glycosylated: helps bind CH2O • Anchored to PM by GPI • Help cell adhesion and cell signaling Plant Cell Wall Proteins 1. HRGP: hydroxyproline-rich glycoproteins (eg extensin) 2. PRP: proline-rich proteins 3. GRP: Glycine-rich proteins 4. Arabinogalactan proteins • Highly glycosylated: helps bind CH2O • Anchored to PM by GPI • Help cell adhesion and cell signaling 5. Also many enzymes involved in cell wall synthesis and loosening Plant Cell Walls and Growth Also many enzymes involved in cell wall synthesis and loosening As growth stops, start making lignins & linking HGRP Plant Cell Walls and Growth As growth stops, start depositing lignins & linking HGRP Lignins = polyphenolic macromolecules: 2nd most abundant on earth (after cellulose) Plant Cell Walls and Growth Lignins = polyphenolic macromolecules: 2nd most abundant on earth (after cellulose) Bond hemicellulose: solidify & protect cell wall (nature’s cement): very difficult to digest Plant Cell Walls and Growth Lignins = polyphenolic macromolecules: 2nd most abundant on earth (after cellulose) Bond hemicellulose: solidify & protect cell wall (nature’s cement): very difficult to digest Monomers are made in cytoplasm & secreted Plant Cell Walls and Growth Monomers are made in cytoplasm & secreted Peroxidase & laccase in cell wall create radicals that polymerise non-enzymatically Plant Cell Walls and Growth Monomers are made in cytoplasm & secreted Peroxidase & laccase in cell wall create radicals that polymerise non-enzymatically Plant Cell Walls and Growth Peroxidase & laccase in cell wall create radicals that polymerise non-enzymatically Very difficult to digest, yet major plant component! Plant Cell Walls and Growth As growth stops, start depositing lignins & linking HGRP Solidify & protect cell wall: very difficult to digest Elongation precedes lignification Plant Cell Walls and Growth As growth stops, start depositing lignins & linking HGRP Solidify & protect cell wall: very difficult to digest Elongation precedes lignification Requires loosening the bonds joining the cell wall Plant Cell Walls and Growth Elongation precedes lignification Requires loosening the bonds joining the cell wall Can’t loosen too much or cell will burst Plant Cell Walls and Growth Elongation precedes lignification Requires loosening the bonds joining the cell wall Can’t loosen too much or cell will burst Must coordinate with cell wall synthesis so wall stays same Plant Cell Walls and Growth Elongation: loosening the bonds joining the cell wall Can’t loosen too much or cell will burst Must coordinate with cell wall synthesis so wall stays same Must weaken crosslinks joining cellulose fibers Plant Cell Walls and Growth Must weaken crosslinks joining cellulose fibers Turgor pressure then makes cells expand Plant Cell Walls and Growth Must weaken crosslinks joining cellulose fibers Turgor pressure then makes cells expand • Lower pH: many studies show that lower pH is sufficient for cell elongation Plant Cell Walls and Growth Must weaken crosslinks joining cellulose fibers • Lower pH: many studies show that lower pH is sufficient for cell elongation Acid growth hypothesis: Growth regulators cause elongation by activating H+ pump Plant Cell Walls and Growth Acid growth hypothesis: Growth regulators cause elongation by activating H+ pump • Inhibitors of H+ pump stop elongation • But: Cosgrove isolated proteins that loosen cell wall • Test protein extracts to see if wall loosens Plant Cell Walls and Growth Acid growth hypothesis: Growth regulators cause elongation by activating H+ pump • But: Cosgrove isolated proteins that loosen cell wall • Test protein extracts to see if wall loosens • Identified expansin proteins that enhance acid growth Plant Cell Walls and Growth Acid growth hypothesis: Growth regulators cause elongation by activating H+ pump • But: Cosgrove isolated proteins that loosen cell wall • Test protein extracts to see if wall loosens • Identified expansin proteins that enhance acid growth • Still don’t know how they work! Plant Cell Walls and Growth • Identified expansin proteins that enhance acid growth • Still don’t know how they work! • Best bet, loosen Hemicellulose/cellulose bonds Plant Cell Walls and Growth Also have endoglucanases and transglucanases that cut & reorganize hemicellulose & pectin Plant Cell Walls and Growth Also have endoglucanases and transglucanases that cut & reorganize hemicellulose & pectin XET (xyloglucan endotransglucosylase) is best-known Plant Cell Walls and Growth Also have endoglucanases and transglucanases that cut & reorganize hemicellulose & pectin XET (xyloglucan endotransglucosylase) is best-known Cuts & rejoins hemicellulose in new ways Plant Cell Walls and Growth XET is best-known Cuts & rejoins hemicellulose in new ways Expansins & XET catalyse cell wall creepage Plant Cell Walls and Growth XET is best-known Cuts & rejoins hemicellulose in new ways Expansins & XET catalyse cell wall creepage Updated acid growth hypothesis: main function of lowering pH is activating expansins and glucanases Plant Cell Walls and Growth Updated acid growth hypothesis: main function of lowering pH is activating expansins and glucanases Coordinated with synthesis of new cell wall to keep thickness constant Plant Cell Walls and Signaling Pathogens must digest cell wall to enter plant Plant Cell Walls and Signaling Pathogens must digest cell wall to enter plant Release cell wall fragments Plant Cell Walls and Signaling Pathogens must digest cell wall to enter plant Release cell wall fragments Many oligosaccharides signal”HELP!” Plant Cell Walls and Signaling Pathogens must digest cell wall to enter plant Release cell wall fragments Many oligosaccharides signal”HELP!” Elicit plant defense responses Growth regulators 1.Auxins 2.Cytokinins 3.Gibberellins 4.Abscisic acid 5.Ethylene 6.Brassinosteroids All are small organics: made in one part, affect another part Growth regulators All are small organics: made in one part, affect another part Treating a plant tissue with a hormone is like putting a dime in a vending machine. It depends on the machine, not the dime! Auxin First studied by Darwins! Showed that a "transmissible influence" made at tips caused bending lower down Auxin First studied by Darwins! Showed that a "transmissible influence" made at tips caused bending lower down No tip, no curve! Auxin First studied by Darwins! Showed that a "transmissible influence" made at tips caused bending lower down No tip, no curve! 1913:Boysen-Jensen showed that diffused through agar blocks but not through mica Auxin 1913:Boysen-Jensen showed that diffused through agar blocks but not through mica 1919: Paal showed that if tip was replaced asymmetrically, plant grew asymmetrically even in dark Auxin 1913:Boysen-Jensen showed that diffused through agar blocks but not through mica 1919: Paal showed that if tip was replaced asymmetrically, plant grew asymmetrically even in dark Uneven amounts of "transmissible influence" makes bend Auxin 1919: Paal showed that if tip was replaced asymmetrically, plant grew asymmetrically even in dark Uneven amounts of "transmissible influence" makes bend 1926: Went showed that a chemical that diffused from tips into blocks caused growth Auxin 1919: Paal showed that if tip was replaced asymmetrically, plant grew asymmetrically even in dark Uneven amounts of "transmissible influence" makes bend 1926: Went showed that a chemical that diffused from tips into blocks caused growth If placed asymmetrically get bending due to asymmetrical growth Auxin 1919: Paal showed that if tip was replaced asymmetrically, plant grew asymmetrically even in dark Uneven amounts of "transmissible influence" makes bend 1926: Went showed that a chemical that diffused from tips into blocks caused growth If placed asymmetrically get bending due to asymmetrical growth Amount of bending depends on [auxin] Auxin 1919: Paal showed that if tip was replaced asymmetrically, plant grew asymmetrically even in dark Uneven amounts of "transmissible influence" makes bend 1926: Went showed that a chemical that diffused from tips into blocks caused growth If placed asymmetrically get bending due to asymmetrical growth Amount of bending depends on [auxin] 1934: Indole-3-Acetic acid (IAA) from the urine of pregnant women was shown to cause bending Auxin 1934: Indole-3-Acetic acid (IAA) from the urine of pregnant women was shown to cause bending IAA is the main auxin in vivo. Others include Indole-3-butyric acid (IBA), 4-Chloroindole-3-acetic acid and phenylacetic acid (PA) IAA 4-CI-IAA IBA PA Auxin IAA is the main auxin in vivo. Many synthetic auxins have been identified IAA Auxin IAA is the main auxin in vivo. Many synthetic auxins have been identified No obvious structural similarity, yet all work! IAA Auxin IAA is the main auxin in vivo. Many synthetic auxins have been identified No obvious structural similarity, yet all work! Widely used in agriculture IAA Auxin IAA is the main auxin in vivo. Many synthetic auxins have been identified No obvious structural similarity, yet all work! Widely used in agriculture • to promote growth (flowering, cuttings) IAA Auxin IAA is the main auxin in vivo. Many synthetic auxins have been identified No obvious structural similarity, yet all work! Widely used in agriculture • to promote growth (flowering, cuttings) • as weed killers! Agent orange was 1:1 2,4-D and 2,4,5-T IAA
