Plant Growth Size & shape depends on cell # & cell size Decide when,where and which way to divide

Plant Growth Size & shape depends on cell # & cell size 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 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 Wall Proteins HRGP: hydroxyproline-rich glycoproteins (eg extensin) 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 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 Peroxidase & laccase in cell wall create radicals that polymerise non-enzymatically Very difficult to digest, yet major plant component!

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 Turgor then drives expansion

Plant Cell Walls and Growth Expansins loosen bonds between Hemicellulose & cellulose Endoglucanases & transglucanases cut & reorganize hemicellulose & pectin XET is best-known Cuts & rejoins hemicellulose in new ways Expansins, endoglucanases & transglucanases catalyse cell wall creepage Activated by low pH

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 Auxins Cytokinins Gibberellins Abscisic acid Ethylene Brassinosteroids Strigolactones 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

IAA IBA 4-CI-IAA PA 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 IBA 4-CI-IAA PA

IAA Auxin IAA is the main auxin in vivo. Many synthetic auxins have been identified IAA

IAA Auxin IAA is the main auxin in vivo. Many synthetic auxins have been identified No obvious structural similarity, yet all work! IAA

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

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

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

IAA Auxin weed killers! Agent orange was 1:1 2,4-D and 2,4,5-T 2,4,5-T was contaminated with dioxin, a carcinogen IAA

IAA Auxin weed killers! Agent orange was 1:1 2,4-D and 2,4,5-T 2,4,5-T was contaminated with dioxin, a carcinogen 2,4-D is still widely used: selectively kills dicots IAA

Auxin weed killers! 2,4-D is still widely used: selectively kills dicots Controls weeds in monocot crops (corn, rice, wheat) Mech unclear: may cause excess ethylene or ABA production. IAA

Auxin weed killers! 2,4-D is still widely used: selectively kills dicots Controls weeds in monocot crops (corn, rice, wheat) Mech unclear: may cause excess ethylene or ABA production. IAA

Auxin >90%of IAA is conjugated to sugars in vivo!

Auxin >90%of IAA is conjugated to sugars in vivo! Inactive, but readily activated!

Auxin >90%of IAA is conjugated to sugars in vivo! Inactive, but readily activated! Best way to measure [auxin] is bioassay!

Auxin >90%of IAA is conjugated to sugars in vivo! Inactive, but readily activated! Best way to measure [auxin] is bioassay! Critical concentration varies between tissues

Auxin >90%of IAA is conjugated to sugars in vivo! Inactive, but readily activated! Best way to measure [auxin] is bioassay! Critical concentration varies between tissues Roots are much more sensitive than leaves!

Auxin Critical concentration varies between tissues Roots are much more sensitive than leaves! Made in leaves & transported to roots so [IAA] decreases going down the plant Most cells are IAA sinks!

Auxin Synthesis Made in leaves & transported to roots so [IAA] decreases going down the plant Most is made from trp

Auxin Synthesis Most is made from trp Also made by trp-independent pathway: exits before trp

Auxin Synthesis Most is made from trp Also made by trp-independent pathway: exits before trp Path used varies between tissues

Auxin Synthesis Most is made from trp Also made by trp-independent pathway: exits before trp Path used varies between tissues No way to run out of IAA

Auxin Levels No way to run out of IAA! [IAA] depends on metabolism

Auxin Levels No way to run out of IAA! [IAA] depends on metabolism Most cells are IAA sinks!

Auxin Levels No way to run out of IAA! [IAA] depends on metabolism Most cells are IAA sinks! IAA is made at shoot apex & transported down: basipetal

Auxin Levels No way to run out of IAA! [IAA] depends on metabolism Most cells are IAA sinks! IAA is made at shoot apex & transported down: basipetal IAA transport therefore affects growth & development

Auxin Transport IAA transport therefore affects growth & development is polar and basipetal: New roots form at base of stem even if stored upside-down

Auxin Transport IAA transport therefore affects development: is polar and basipetal. New roots form at base of stem even if stored upside-down. Stem sections only move IAA basipetally

Chemiosmotic Auxin Transport Apoplastic IAAH diffuses into cell IAAH due to low pH

Chemiosmotic Auxin Transport Apoplastic IAAH diffuses into cell IAAH due to low pH AUX1 pumps in IAA- -

Chemiosmotic Auxin Transport Apoplastic IAAH diffuses into cell IAAH due to low pH AUX1 pumps in IAA- 2. In cell IAAH-> IAA- due to pH 7.2 -

Chemiosmotic Auxin Transport Apoplastic IAAH diffuses into cell IAAH due to low pH AUX1 pumps in IAA- 2. In cell IAAH-> IAA- due to pH 7.2, , draws more IAAH -

Chemiosmotic Auxin Transport Apoplastic IAAH diffuses into cell IAAH due to low pH AUX1 pumps in IAA- 2. In cell IAAH-> IAA- due to pH 7.2, draws more IAAH 3. IAA- is pumped out by PIN proteins in basal part of cell -

Chemiosmotic Auxin Transport Apoplastic IAAH diffuses into cell IAAH due to low pH AUX1 pumps in IAA- 2. In cell IAAH-> IAA- due to pH 7.2, draws more IAAH 3. IAA- is pumped out by PIN proteins in basal part of cell 4. In apoplast IAA- -> Cycle repeats

Chemiosmotic Auxin Transport Supporting evidence Some chemicals specifically block import or export

Chemiosmotic Auxin Transport Supporting evidence Some chemicals specifically block import or export Export blockers stop efflux into block, no effect on uptake

Chemiosmotic Auxin Transport Supporting evidence Some chemicals specifically block import or export Export blockers stop efflux into block, no effect on uptake Import blockers stop uptake

Chemiosmotic Auxin Transport Supporting evidence Some chemicals specifically block import or export Export blockers stop efflux , no effect on uptake Import blockers stop uptake Both mess up development!

Chemiosmotic Auxin Transport Supporting evidence Some chemicals specifically block import or export Export blockers stop efflux , no effect on uptake Import blockers stop uptake Both mess up development! Natural transport inhibitors have anti-cancer activity!

Chemiosmotic Auxin Transport Supporting evidence Some chemicals specifically block import or export Export blockers stop efflux , no effect on uptake Import blockers stop uptake Both mess up development! Natural transport inhibitors have anti-cancer activity! Genistein binds estrogen receptors

Chemiosmotic Auxin Transport Supporting evidence Some chemicals specifically block import or export Both mess up development! 2.AUX1 encodes an IAA-H+ symporter found at top of cell

Chemiosmotic Auxin Transport Supporting evidence Some chemicals specifically block import or export Both mess up development! 2.AUX1 encodes an IAA-H+ symporter found at top of cell aux1 resemble plants treated with import blockers

Chemiosmotic Auxin Transport Supporting evidence Some chemicals specifically block import or export 2.AUX1 encodes an IAA-H+ symporter found at top of cell aux1 resemble plants treated with import blockers 3. PINs encode IAA exporters found at cell base

Chemiosmotic Auxin Transport Supporting evidence Some chemicals specifically block import or export 2.AUX1 encodes an IAA-H+ symporter found at top of cell aux1 resemble plants treated with import blockers 3. PINs encode IAA exporters found at cell base pin1 resemble plants treated with export blockers