cooper1 - Plant Physiology Plants are successful on Earth...

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Plant Physiology • Plants are successful on Earth –big (100m tall), long life span (10,000 years) • Plants are important to humans • Primary Producers –“Food” for all consumers • Source of polymers and chemicals –Fuel, Fiber –Flavors, Fragrances –Farmaceuticals 1 Lecture 4 Basic Plant Architecture Photosynthesis Overview of plant architecture • Cellular differences from animals Cell wall: structure and implications • Overview of anatomy Tissue types and organization Cell wall Composition of cell wall • 25-30% cellulose (major structural component) • 40-55% other polysaccharides • 1-15% protein • Fully hydrated Walls critical for structure, but also site of cell-cell contact and communication = linear glucose polymer, lots of H-bonding potential
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Organization of cellulose and other polysaccharides in wall matrix Microfbrils composed oF 30-250 linear molecules H-bonded together Length varies From 2000-25000 Glc residues per molecule Cross-linked by other polysaccharides • Fiber-reinforced cell wall is strong --> Osmosis can build up high internal hydrostatic pressure (turgor pressure) • Cell growth depends on turgor to stretch walls Plant cells can elongate up to 200x •Elongation/expansion requires turgor pressure (up to ~10 atm) and wall loosening •Major increase in cell volume occurs in vacuole, not cytoplasm •Direction of expansion is always perpendicular to cellulose micro±brils •Orientation of cellulose deposition determines orientation of growth Orientation of cellulose micro±brils in elongating cell walls •Cell expansion is accompanied by new cell wall synthesis •Old micro±brils shift to more vertical orientation as cell elongates •Deposition of new micro±brils at cell surface continues perpendicular to long axis of cell -> maintains orientation of expansion Plant secondary walls •Highly regular array of cellulose •Micro±brils often ~10x longer than in primary walls -> very rigid •No further expansion possible •Often include specialized polymers • SUBERIN (wax) or LIGNIN (plastic) 12 Cotton fiber cell walls 99.99% cellulose
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13 Wood (xylem) cell wall: ~50% Cellulose ~50% Lignin Lignin = crosslinked polyphenolicn resin Very resistant to biodegradation, and chemical degradation 14 Phenylalanine PAL, Phenylalanine Ammonia Lyase Crosslinked by Peroxidase PhenylPropanoids secreted into wall. infused throughout cellulose network 15 LignoCellulosic cell walls structured like fiberglass Strong cellulose fibers crosslinked lignin resin Strong glass fibers crosslinked epoxy resin Formation of new cell wall Vesicles coalesce at cell plate Vesicles fuse to form middle lamella (with some gaps) Daughter cells secrete wall material at PM surface Results in age gradient within wall Formation of new cell wall Daughter cells secrete wall material at PM surface Secondary cell wall laid down inside primary cell wall. Results in age gradient
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cooper1 - Plant Physiology Plants are successful on Earth...

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