Lesson 7: Plant Cell Wall

cell wall

thick wall outside the plasma membrane that can be several microns thick, ECM surrounding plant cells

Cellulose microfibrils

• Long, thin polysaccharide fiber that helps strengthen plant cell walls

  • Interwoven with other polysaccharides and some structural proteins bonded to form a complex structure that resists both compression and tension 

Lignin

• a complex polymer, a highly cross-linked network in woody tissue

  • Makes matrix more rigid and waterproof 

Pectin

• provides resistance to compression, fills spaces between the microfibrils 

  • Especially middle lamella, green strands in diagram below  

structure of cell wall

middle lamella, primary cell wall, secondary cell wall, plasma membrane 

middle lamella

Outermost layer, shared by all adjacent cells

• Acts as a cementing material that binds the cells together 

• Composed of pectins and proteins

• Formed during cytokinesis from vesicles originating in golgi 

• has phragmoplast 

phragmoplast

• Give rise to plasma membranes of daughter cells at plate 

• What is formed in a cell to divide it into 2 different cells (equitoral plate in plants)

• What forms cell wall → vesicles come from golgi fuse in middle to form it

plasmodesmata

Direct communication channels between the cytoplasm of adjacent cells that allow the free passage of substances

• connections between 2 daughter cells 

• tiny holes 

  • ER from both daughter cells is connected 

primary cell wall

• Thicker, composed of cellulose that forms fibers (microfibrils have chains arranged parallelly)

• Cellulose gives cell wall its rigidity 

• Composition

  • Cellulose microfibrils

  • Hemicellulose molecules

• pectins and structural proteins

secondary cell wall

• Present in only certain types of cells

• Forms after primary cell wall after cell has stopped growing 

• Primarily mechanical function 

• 3 sublayers: S1, S2 and S3 (from outside in)

Desmotubule

•  tube-shaped structure often observed passing through the plasmodesma 

  • Located in center w/out occupying the entire space and is connected to the ER 

Pits

inhibitions of secondary wall deposition at level of a cluster of plasmodesmata, where both the thickening wall and the subsequent deposition of the secondary wall have been inhibited  

• Places w/out secondary cell wall, primary cell wall is thinner 

• Need to have holes for communication

Bordered pits:

• secondary wall forms a projection or rim w/out completely covering the cluster of plasmodesmata 

torus

• lens-shaped thickening formed by the primary wall and middle lamella 

  • Acts as a valve in response to pressure differences between cells