Plant tissues

• Plant cells


  The basic structural and functional units that the plant body is composed of. Cells are the building blocks of the organism.
• Plant tissue


  An ensemble of similar cells from the same origin that together carry out a specific function. Organs are then formed by the functional grouping together of multiple tissues.
• Two major types of plant tissues

  • Meristematic tissue
  • Permanent tissue
• Meristematic tissue


  • Cells are roughly spherical or polyhedral, rectangular-shaped, thin-walled and tightly packed. They have a large nucleus with small or no vacuole. They are actively dividing cells that facilitate growth in length and thickness.
• Meristem


  An area composed of cells whose principal function is the formation and production of new cells
• Types of meristematic tissue

  • Apical meristem
  • Lateral meristem
  • Intercalary meristem
• Apical meristem


  • Present at the shoot apex (where primary stem, leaves, and flowers differentiate) and at the root apex (where primary root tissue is produced). They form growing parts at the apices of roots and stems and are responsible for the increase in length, also called primary growth.
• Intercalary meristem


  • Located in between permanent tissues, usually at the base of the node, internode, and leaf base. They are responsible for growth in the length of the plant and by increasing the size of the internode, they result in branch formation and growth. They are also responsible for primary growth.
• Lateral meristem


  • Located parallel to the long axis of a shoot or root, most commonly in the pericyclic region, at the junction between vascular tissue and the cortex. This meristem consists of cells that mainly divide in one plane and cause the organ to increase in diameter and growth. Lateral meristem usually occurs beneath the bark of the tree in the form of cork cambium and in vascular bundles of dicots in the form of the vascular cambium. The activity of this cambium results in the formation of secondary growth.
• Primary growth


  The initial growth of a shoot or root and the generation of leaves and flowers. The plant stem and root elongate i.e. increase in length by cell enlargement. The growth occurs in areas called apical meristems.
• Secondary growth


  The transition from primary growth to secondary growth. Secondary growth is an increase in the thickness of existing stems and roots due to lateral meristems.
• Vascular cambium


  A cylinder of tissue that extends throughout the length of the plant from the tips of the shoots to the tips of the roots. It is present in all perennials and in some annual plants. Tissues produced by cell divisions of the vascular cambium are secondary tissues.
• Cork cambium


  Found in the bark of roots and stems of woody plants where they produce cork cells. The cork cambia originate just under the epidermis of the primary body and in some tree species are long cylinders running parallel to the vascular cambium.
• There are three processes that facilitate plant growth: cell division, cell elongation, and cell differentiation.
• Some epidermal cells have specialized functions such as guard cells (stomata) or trichomes (hairs).
• Types of permanent tissues

  • Simple permanent tissues
  • Complex permanent tissues
  • Special or secretory tissues (glandular)
• Parenchyma


  • Relatively unspecialized living cells with thin cell walls that are usually loosely packed so that intercellular spaces are found between cells of this tissue. This tissue provides support to plants and also stores food. In some situations, parenchyma contains chlorophyll and performs photosynthesis, in which case it is called chlorenchyma. In aquatic plants, large air cavities are present in parenchyma to give support to them to float on water. Such a parenchyma type is called aerenchyma.
• Collenchyma


  • A living tissue of primary body like parenchyma. Cells are irregularly thick-walled, possess thickening of cellulose, water and pectin substances (pectocellulose) at the corners where number of cells join together. This tissue gives a tensile strength to the plant and the cells are compactly arranged and have very little inter-cellular spaces.
• Sclerenchyma


  • Tissue consists of thick-walled, dead cells (protoplasm is absent). These cells have hard and extremely thick secondary walls due to uniform distribution of lignin. Lignin deposition is so thick that the cell walls become strong, rigid and impermeable to water. Sclerenchyma cells have a narrow lumen and are long and narrow.
• Types of Sclerenchyma cells


  • Sclereid
  • Fiber
• Sclereid


  Irregularly shaped, dead at maturity, and common in shells of nuts, hard seeds, and stones of fruit (cherry or peach).
• Fiber


  Very long, narrow, thick, and lignified sclerenchyma cells.
• Pectocellulose


  • Thickening of cellulose, water and pectin substances at the corners where number of cells join together
  • Gives tensile strength to the plant
  • Cells are compactly arranged with little intercellular spaces
  • Occurs chiefly in hypodermis of stems and leaves
  • Absent in monocots and in roots
• Collenchyma


  Collenchymatous tissue that acts as a supporting tissue in stems of young plants
• Collenchyma


  • Provides mechanical support, elasticity, and tensile strength to the plant body
  • Present in the margin of leaves and resist tearing effect of the wind
• Parenchyma and collenchyma cells
• Sclerenchyma


  Tissue consisting of thick-walled, dead cells (protoplasm is absent)
• Sclerenchyma


  • Cells have hard and extremely thick secondary walls due to uniform distribution of lignin
  • Lignin deposition is so thick that the cell walls become strong, rigid and impermeable to water
  • Cells have a narrow lumen and are long and narrow
• Types of Sclerenchyma cells


  • Sclereid
  • Fiber
• Sclereid


  Irregularly shaped, dead at maturity, common in shells of nuts, hard seeds, and stones of fruit (cherry or peach)
• Fiber


  Very long, narrow, thick, and lignified cells that are pointed at both ends
• Complex permanent tissue


  Consists of more than one type of cells which work together as a unit
• Complex tissue


  • Protects all parts of the plant, regulates water loss, and exchange of gases
  • Helps in the transportation of organic material, water and minerals up and down the plants
  • Also known as conducting and vascular tissue
• Common types of complex permanent tissue

  • Epidermis
  • Xylem or wood
  • Phloem or bast
• Epidermis


  The entire surface of the plant consisting of a single outer layer of cells
• Epidermis tissue cell types

  • Epidermis cells
  • Guard cells
  • Trichomes
• Epidermis cells


  • Relatively flat
  • Outer and lateral walls are often thicker than the inner walls
  • Form a continuous sheet without intercellular spaces
  • Do not have chloroplast and are transparent to accommodate photosynthetic tissue underneath
• Guard cells


  Specialized cells in the epidermis
• Trichomes


  Outgrowths or hairs on the epidermis with various forms and sizes
• Epidermis


  • Protects all parts of the plant and controls water loss in the aerial parts
  • Epidermal cells prevent water loss through secretion of waxy layer called cuticle
  • Stomata controls diffusion of carbon dioxide, oxygen and water vapour