Cell wall Independent Study Flashcards
Functions of cell wall
Regulate volume
Determine cell shape
Regulate turgor pressure
Mechanical protection
Diffusion barrier - ionic and sieve
Sensory mechanism
Barrier to pathogens
Provide structure for water flow
Cellulose microfibrils
high tensile strength
linear, only one type of glucose unit
3nm
Beta-linked glucans
insoluable
macrofibril bundles - woody
structural bias
sites of disorder where pectins woven in
hydrophillic surfaces -OH extend from sides
hydrophobi CH groups
tight structure wards enzyme attack
made by cellulose synthase complex in PM
Pectin
-Gel-forming polysaccharide matrix to embed cellulose
-soluable
-determines cell porosity
-rich in acid-sugar residues
-high water content
-cell walls can expand
-neutral side chains bind to cellulose
-covalent to hemicellulose
-ionic bonds of pectin by Ca2+
Hemicellulose
-Matrix polysaccharide
-more random amorphous structure
- B-linked backbones - planar
-different sugars
-weaker
- tightly bound to cellulose, alters crystallization
-xyloglucan most dominant form
-fewer side chains can bind tight
- arabionxylan in grass - less digestible
non-enzymatic proteins
-2-10% of dry mass of cell
-exact function uncertain
- short motifs of repeating AA or high degree of glycosylation
-HRGP
-PRP
-GRP
-AGp
HRGP
hydroxyproline rich glycoprotein
- in cambium, vascular parenchyma
PRP
proline rich protein
- in xylem, fibers, cortex, root hairs
GRP
Glycine-rich
- in primary xylem and phloem
AGP
Arabinogalacten protein
-cell adhesion and differentation
Two types of cell expansion
tip growth and diffuse
Tip growth
- localized wall expansion
- root hairs and pollen tubes
- cytoskeletal - actin microfibrils
- growing wall doubles surface area in minutes
-coordinated so doesn’t burst
Diffuse growth
- actin flimaments
- not fibers/sclerids/trichomes
- 1-10% growth per hour
- growth influenced by microfibril direction
- cell wall extended by turgor pressure
- isodiametric at meristems - sphere
–anisotropic - if constrained - slower growth rate on some sides has more CA2+
what effect do microtubule poisons have on directionality of plant expansion and why?
-bind to tubulin (subunit of microtubule), depolymerize, leads to isotropic growth
-round expansion instead of directional - tumour like growth
-disrupts microtubule tracts
possible modifications of maturing cell that lead to wall rigidification
- reduction of loosening process (unforming/reforming cellulose matrix)
- increase cell-wall cross-linking
- alteration cell wall composition
- new matrix polysaccharides - tighter
- removal of 1,3,1,4B-D glucan in grass
- de-estrification of pectins
- cross-linking of tyrosine and ferulic acid residues
- microtubules reorient parallel to growth axis
