FPU L4Woody Plant Cell

• What makes the plant cell UNIQUE?

  • The plant cell wall is a remarkable structure
  • It provides the most significant difference between plant cells and other eukaryotic cells
  • The cell wall is rigid (up to many micrometers in thickness) and gives plant cells a very defined shape
  • The first cell wall of growing cells is called the primary cell wall
  • The cell wall layers could be differentiated based on microfibrillar orientation, microfibrillar angle, and thickness
• Chemical Components of the Cell Wall

  • Carbohydrates (sugar molecules)
  • Cellulose (40 to 50%) - the main component of the cell wall in most plants
  • Hemicellulose (20 to 35%) - polysaccharides more or less ordered than cellulose
  • Lignin (15 to 35%) - the cementing substance of the wood
  • Extraneous Materials (20 to 25%) - include tannins, volatile oils, resins, gums, latex, alkaloids, and other complex organic compounds
• Primary Cell Wall Layer

  • Thin-walled, capable of being extensively increased in surface
  • Irregular interwoven orientation of microfibrils (primary-wall texture) provides greater length than diameter increase of cell
  • Provides strength and flexibility
• Secondary Cell Wall Layer

  • The most striking feature of secondary walls is their loss of plasticity
  • Progressive depositions of new lamellas thicken the wall while the cell lumen's diameter decreases
  • Less hydrated than primary walls and contain less pectins and hemicellulose
  • S1 - the first formed layer with high tensile strength
  • S2 - the thickest among the secondary wall layers, greatly influencing many properties of wood
• Microfibrillar orientation can be either a Z or S helix
• Microfibrillar angle and thickness differentiate cell wall layers
• Secondary wall layers


  • Layer S1 has high tensile strength
  • Layer S2 is the thickest among the secondary wall layers, influencing dimensional change along radial and tangential directions
  • Layer S3 is the last formed layer, also known as the "tertiary wall" with significantly different features compared to other layers
• Modifications or Sculpturing of the Cell Wall

  • Pit
  • Perforation
  • Spiral Thickening
  • Dentations
  • Crassulae
  • Trabeculae
  • Septations
  • Wart Structure/Layer
• Pit


  1. A recess or opening in the secondary wall, serves as a passage of moisture and other substances between cells

  2. There are two types of pits: simple and bordered

  3. Prosenchymatous elements have bordered pits, and parenchymatous elements have simple pits

  4. When two elements are positioned adjacent, they may form pit pairs

  5. There are three types of pit pairs: simple pit pair, bordered pit pair, and half-bordered pit pair

  6. Provide communication between adjacent cells
• Perforation


  1. Openings that occur in the common-end walls of two vertically contiguous vessel elements

  2. Provide communication between adjacent cells
• Spiral Thickening


  1. Ridges on the inner face of the secondary wall in the form of single or multiple helices around the cell

  2. Deposition of additional layers of material in a spiral pattern around the cell wall

  3. This modification provides additional structural support to the cell
• Dentations


  1. Tooth-like thickenings found in the ray tracheid of some species of conifers

  2. Help anchor the cell to its surroundings
• Crassulae


  1. Thicker, generally arching portions of the intercellular layer above and below the primary pit fields

  2. A crassula appears to be localized thickening of the primary wall which may serve as stiffening around the primary pit field
• Trabeculae


  1. Rod-like extensions across the cell lumen from wall to wall in conifers

  2. Associated with fungal activity

  3. Provide additional structural support to the cell
• Septations


  1. Transverse partitions in hardwood fiber

  2. May occur as a normal feature in some tropical hardwood species

  3. Regulate the movement of materials within the cell, separate incompatible processes
• Wart Structure/Layer


  1. Deposited remains of the cytoplasm formed in the innermost layer of the cell

  2. The presence affects the diffusion of water, preservatives, and pulping liquids

  3. Help protect the cell from environmental stressors such as abrasion or pathogens
• Lignin is deposited between cells to form secondary walls that are thicker than primary walls.
• The primary cell wall is composed mainly of cellulose, with hemicelluloses (xylans) as the major non-cellulosic polysaccharides.
• Secondary walls can be further subdivided into S1, S2, and S3 layers based on their thickness and composition.
• The lignified middle lamella binds adjacent cells together.
• Secondary growth occurs through the addition of new layers of xylem and phloem tissue on the outside of existing vascular bundles.
• Pectins are also present in small amounts.
• Xylem vessels become elongated and narrowed during secondary growth.
• Pectins are also present in small amounts.
• Secondary cell walls contain lignin, which provides strength and rigidity to the plant tissue.
• S1 layer: Thinnest layer, contains pectins and lignin.
• Secondary cell walls contain lignin, which provides strength and rigidity to the plant tissue.
• S2 layer: Middle layer, contains more lignin and less pectin compared to S1.
• Secondary cell walls contain lignin, which provides strength and rigidity to the plant tissue.
• Pits are openings in the secondary wall through which plasmodesmata connect neighboring cells.
• Tracheids have tapered end walls called bordered pits, while vessels lack them.
• Secondary cell walls contain lignin, which provides strength and rigidity to the plant tissue.
• Pits are openings in the secondary wall through which plasmodesmata connect neighboring cells.
• Tracheids have tapered end walls called bordered pits, while vessels lack them.
• Perforation plates are specialized pits found at the ends of tracheid elements.