DOC PREVIEW
BYU PWS 440 - chapter 15_ Cell walls (1)

This preview shows page 1-2-3-4-5 out of 14 pages.

Save
View full document
View full document
Premium Document
Do you want full access? Go Premium and unlock all 14 pages.
Access to all documents
Download any document
Ad free experience
View full document
Premium Document
Do you want full access? Go Premium and unlock all 14 pages.
Access to all documents
Download any document
Ad free experience
View full document
Premium Document
Do you want full access? Go Premium and unlock all 14 pages.
Access to all documents
Download any document
Ad free experience
View full document
Premium Document
Do you want full access? Go Premium and unlock all 14 pages.
Access to all documents
Download any document
Ad free experience
View full document
Premium Document
Do you want full access? Go Premium and unlock all 14 pages.
Access to all documents
Download any document
Ad free experience
Premium Document
Do you want full access? Go Premium and unlock all 14 pages.
Access to all documents
Download any document
Ad free experience

Unformatted text preview:

Slide 1Slide 2Slide 3Slide 4Slide 5Slide 6Slide 7Slide 8Slide 9Slide 10Slide 11Slide 12Slide 13Slide 14Chapter 15: Cell wallsCell wall structurePrimary cell wall 1) produced early in cell development 2) thin and expandable Secondary cell wall 1) thick, does not expand, therefore they form after cell growth ceases, can make up to 90% weight in large trees Middle lamella- interspace between cell wallsPrimary wall composition: cellulose microfibrils Cellulose microfibrils- glucan chains (glucose polymer) woven into strands extremely stable with high tensile strength Synthesized on the plasma membrane by a rosette unit (“cell loom”) Rosette composed of 6 subunits composed of 6 cellulose synthase enzymes Cellulose synthase produces glucan chains by linking glucose monomers derived from the hydrolysis of sucrosePrimary wall composition: matrix polymers Hemicelluloses: flexible polysaccharides that form tethers that bind microfibrils into a cohesive network Pectins: hydrated gel in which microfibril-hemicellulose network is embedded Hemicellulose-pectin matrix is 80% water giving primary cell walls extensibility Hemicelluloses and pectins are sythesized by glycosyltranferases in Golgi apparatus and delivered to the cell wall via exocytosis Evidence for self-assembly and enzyme mediated cell wall assemblyNon-covalent bonding contributes to cell wall linkagesGroups of neighboring pectin chains are linked together via Ca2+ Negative carboxyl groups bind to calcium’s positive chargePatterns of cell expansionMicrofibril orientation influences growth directionality Because microfibrils resist expansion, cell growth occurs perpindicular to microfibril orientationSecondary wall composition Secondary walls form after cell expansion ceases cellulose microfribrils impregnated with lignin Function of lignin 1) increase structural strength in stems and branches 2) prevents the collapse of xylem during periods of high water tension 3) hydrophobic, which reduces susceptibility to pathogen enzymes 4) decreases palatability of plant tissue to herbivoresCell wall function Provides protection (insects, pathogens) Rigidity & strength to defy gravity (“cell exoskeleton”) Defines cell shape, size and direction of growth Diffusion barrier to large macromolecules Nutrient reservoir Influences cell and tissue water balance How? Cell:Tissue: Water holding capacity & rate of water movement in apoplastWater potential Ψ = (-)osmotic potential + pressure potentialAuxins stimulate growth by cell wall relaxationAuxin mutantsHow do cells stimulate cell expansion?Observation: cells expand under acidic conditions (ph 4.5)How would acidic conditions promote cell wall extension?Through Ca2+ exhangeHow do cells acidify the cell wall space? ATP driven proton pumpsCell wall extension is mediated by ExpansinsExpansins loosen non-covalent adhesion between cell wall polysaccharides; evidence suggest they may relax the microfibril-hemicelluose linkagesCell wall degradationDevelopmental cell wall degradation Enzymes mediate wall hydrolysis & degradation during fruit ripening, leaf abscissionDefense signaling Fungal released pectinases hydrolyze cell wall releasing defense elicitors Plants release chitinases & glucanases that hydrolize fungal cell wall components that serve as defense elicitorsCell growth: applying your knowledgeWater potential Ψ = (-)osmotic potential + pressure potentialWhat would need to happen at the cellular level for this circular cell to growth horizontally?1) Increase in cell turgor (expansion capacity)2) Need influence direction of growthOrientation of cellulose microfibrilsChapter 15 Homework questionsDescribe the components and processes that plant cells use to produce their primary cell wallHow do primary and secondary walls differ and explain the function of eachWith the water potential equation as your guide and a knowledge of the action of auxins and expansins on cell wall function, explain the steps that are required for cell expansion to occur. Explain how the directionality of cell growth is


View Full Document

BYU PWS 440 - chapter 15_ Cell walls (1)

Download chapter 15_ Cell walls (1)
Our administrator received your request to download this document. We will send you the file to your email shortly.
Loading Unlocking...
Login

Join to view chapter 15_ Cell walls (1) and access 3M+ class-specific study document.

or
We will never post anything without your permission.
Don't have an account?
Sign Up

Join to view chapter 15_ Cell walls (1) 2 2 and access 3M+ class-specific study document.

or

By creating an account you agree to our Privacy Policy and Terms Of Use

Already a member?