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