The Plant Cell Wall

·         The plant cell wall is heterogeneous structure composed of layers (lamellae)

§  Each cell secretes its own wall

§  Junction between the walls is the Middle lamella

§  Cell wall is penetrated by plasmodesmataconnecting neighbouring cells

§  Cell walls are primarily composed of sugar polymers i.e. polysaccharides

§  The architecture, mechanics, and function of plants depend crucially on structure of cell wall

·         Functions 

§  Regulates cell volume by limiting protoplast size preventing cell rupture

§  Determines cell shape

§  Involved in cell-cell adhesion; provide support to cells and whole plant

§  Forms specialized structures for:

§  Transport of water and nutrients

§  Defense against bacterial and fungal attack

§  Reproduction

·         Composition of Cell Walls

§  Primary cell wall:

§  Which is the only cell wall in growing and dividing cells

§  First formed cell wall

§  Composed of cellulose embedded in matrix of hemicelluloseand pectin, cellulosemolecules: Unbranched glucose chains and hemicellulose – a highly branched molecule of sugars and sugar derivatives

§  Pectins:

·         Are highly branched negatively charged polysaccharides rich in galacturonic acid

·         Give compressive strength to the cell wall

·         Modulate porosity, pH, and ion concentrations within the wall

§  Primary wall/Middle Lamellae

§  Primarily associated with hemicellulosesand pectins

§  Water is 65% of weight of cell wall

§  Secondary Cell Wall

§  Many plant cells synthesize secondary walls after the cell has completely elongated

§  Secondary wall is deposited by protoplast inside primary wall after cell stops growing

§  Composition of secondary wall:

·         Cellulose, hemicellulose and pectin

·         Lignin

·         Stronger than cellulose

·         There substances found on the surface of the cell wall. These include cuticle waxes, suberin and minerals

Blue Water Wallpaper

Evans, W. C. (2009). Trease and Evans Pharmacognosy. India: Reed Elsevier Limited.

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