Plant Cell Walls and Growth 1 walls 25
- Slides: 72
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
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 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 CH 2 O • 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: 2 nd most abundant on earth (after cellulose)
Plant Cell Walls and Growth Lignins = polyphenolic macromolecules: 2 nd 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: 2 nd 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 p. H: many studies show that lower p. H is sufficient for cell elongation
Plant Cell Walls and Growth Must weaken crosslinks joining cellulose fibers • Lower p. H: many studies show that lower p. H 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 p. H is activating expansins and glucanases
Plant Cell Walls and Growth Updated acid growth hypothesis: main function of lowering p. H 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
Light regulation of Plant Development Plants use light as food and information Use information to control development
Light regulation of Plant Development Plants use light as food and information Use information to control development • germination
Light regulation of Plant Development Plants use light as food and information Use information to control development • Germination • Photomorphogenesis vs skotomorphogenesis
Light regulation of Plant Development Plants use light as food and information Use information to control development • Germination • Photomorphogenesis vs skotomorphogenesis • Sun/shade & shade avoidance
Light regulation of Plant Development • Germination • Morphogenesis • Sun/shade & shade avoidance • Flowering
Light regulation of Plant Development • Germination • Morphogenesis • Sun/shade & shade avoidance • Flowering • Senescence
Light regulation of growth Plants sense 1. Light quantity
Light regulation of growth Plants sense 1. Light quantity 2. Light quality (colors)
Light regulation of growth Plants sense 1. Light quantity 2. Light quality (colors) 3. Light duration
Light regulation of growth Plants sense 1. Light quantity 2. Light quality (colors) 3. Light duration 4. Direction it comes from
Light regulation of growth Plants sense 1. Light quantity 2. Light quality (colors) 3. Light duration 4. Direction it comes from Have photoreceptors that sense specific wavelengths
Light regulation of growth Early work: • Darwin showed that phototropism is controlled by blue light
Light regulation of Plant Development Early work: • Darwins : phototropism is controlled by blue light • Duration = photoperiodism (Garner and Allard, 1920) Maryland Mammoth tobacco flowers in the S but not in N
Light regulation of Plant Development Early work: • Darwins : phototropism is controlled by blue light • Duration = photoperiodism (Garner and Allard, 1920) Maryland Mammoth tobacco flowers in the S but not in N = short-day plant (SDP)
Light regulation of Plant Development Duration = photoperiodism (Garner and Allard, 1920) Maryland Mammoth tobacco flowers in the S but not in N = short-day plant (SDP) Measures night! 30" flashes during night stop flowers
Light regulation of growth Duration = photoperiodism (Garner and Allard, 1920) Maryland Mammoth tobacco flowers in the S but not in N = short-day plant (SDP) Measures night! 30" flashes during night stop flowers LDP plants such as Arabidopsis need long days to flower
Light regulation of growth Duration = photoperiodism (Garner and Allard, 1920) Maryland Mammoth tobacco flowers in the S but not in N = short-day plant (SDP) Measures night! 30" flashes during night stop flowers LDP plants such as Arabidopsis need long days to flower SDP flower in fall, LDP flower in spring, neutral flower when ready
Light regulation of growth Measures night! 30" flashes during night stop flowers LDP plants such as Arabidopsis need long days to flower SDP flower in fall, LDP flower in spring, neutral flower when ready Next : color matters! Red light works best for flowering
Light regulation of growth Next : color matters! Red light (666 nm)works best for flowering & for germination of many seeds!
Phytochrome Next : color matters! Red light (666 nm)works best for flowering & for germination of many seeds! But, Darwin showed blue works best for phototropism!
Phytochrome Next : color matters! Red light (666 nm)works best for flowering & for germination of many seeds! But, Darwin showed blue works best for phototropism! Different photoreceptor!
Phytochrome But, Darwin showed blue works best for phototropism! Different photoreceptor! Red light (666 nm) promotes germination Far red light (>700 nm) blocks germination
Phytochrome But, Darwin showed blue works best for phototropism! Different photoreceptor! Red light (666 nm) promotes germination Far red light (>700 nm) blocks germination
Phytochrome Red light (666 nm) promotes germination Far red light (>700 nm) blocks germination After alternate R/FR flashes last flash decides outcome
Phytochrome Red light (666 nm) promotes germination Far red light (>700 nm) blocks germination After alternate R/FR flashes last flash decides outcome Seeds don't want to germinate in the shade!
Phytochrome Red light (666 nm) promotes germination Far red light (>700 nm) blocks germination After alternate R/FR color of final flash decides outcome Seeds don't want to germinate in the shade! Pigment is photoreversible
Phytochrome Red light (666 nm) promotes germination Far red light (730 nm) blocks germination After alternate R/FR color of final flash decides outcome Pigment is photoreversible! -> helped purify it! Looked for pigment that absorbs first at 666 nm, then 730
Phytochrome Red light (666 nm) promotes germination Far red light (730 nm) blocks germination After alternate R/FR color of final flash decides outcome Pigment is photoreversible! -> helped purify it! Looked for pigment that absorbs first at 666 nm, then 730
Phytochrome Red light (666 nm) promotes germination Far red light (730 nm) blocks germination After alternate R/FR color of final flash decides outcome Pigment is photoreversible! -> helped purify it! Looked for pigment that absorbs first at 666 nm, then 730 Made as inactive cytoplasmic Pr that absorbs at 666 nm
Phytochrome Made as inactive cytoplasmic Pr that absorbs at 666 nm or in blue Converts to active Pfr that absorbs far red (730 nm)
Phytochrome Made as inactive cytoplasmic Pr that absorbs at 666 nm or in blue Converts to active Pfr that absorbs far red (730 nm) 97% of Pfr is converted back to Pr by far red light
Phytochrome Made as inactive cytoplasmic Pr that absorbs at 666 nm or in blue Converts to active Pfr that absorbs far red (730 nm) 97% of Pfr is converted back to Pr by far red light Also slowly reverts in dark
Phytochrome Made as inactive cytoplasmic Pr that absorbs at 666 nm or in blue Converts to active Pfr that absorbs far red (730 nm) 97% of Pfr is converted back to Pr by far red light Also slowly reverts in dark: how plants sense night length
Types of Phytochrome Responses Two categories based on speed 1. Rapid biochemical events 2. Morphological changes
Types of Phytochrome Responses Two categories based on speed 1. Rapid biochemical events 2. Morphological changes Lag time also varies from minutes to weeks
Types of Phytochrome Responses Two categories based on speed 1. Rapid biochemical events 2. Morphological changes Lag time also varies from minutes to weeks: numbers of steps after Pfr vary
Types of Phytochrome Responses Lag time also varies from minutes to weeks: numbers of steps after Pfr vary "Escape time" until a response can no longer be reversed by FR also varies
Types of Phytochrome Responses Lag time also varies from minutes to weeks: numbers of steps after Pfr vary "Escape time" until a response can no longer be reversed by FR also varies: time taken for Pfr to do its job Conclusions: phytochrome acts on many processes in many ways
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