BOT 119 Handout 12: Parenchyma

• Parenchyma


  A tissue composed of living cells variable in their morphology and physiology, but generally having thin walls and a polyhedral shape and concerned with vegetative activities of the plant

  
  

  The individual cells of such tissue are parenchyma cells

  
• Parenchyma cells


  • Living protoplasts - can resume meristematic activity and give rise to new cells, totipotent, principal seat of essential cellular activities
  • Thin primary walls - important in wound healing, regeneration, formation of adventitious organs, union of grafts
  • Unspecialized morphologically and physiologically - may change functions or combine several different ones

  
• Where does parenchyma cells occur in the plant body?

  • Pith
  • Pith ray cortex
  • Mesophyll
  • Ground tissue of reproductive structures
  • Associated with primary and secondary vascular tissues
  • Phelloderm

  
• Origin of parenchyma cells

  1. Ground meristem

  2. Procambium/Vascular cambium

  3. Cork cambium

  
• General structure and appearance of parenchyma cells

  • Polyhedral - many sides or facets, but no single pattern of shape
  • Isodiametric: ground tissues of stem and root
  • Lobed: gymnosperm mesophyll
  • Irregular/branched: spongy mesophyll
  • Elongated: prosenchyma of the palisade mesophyll
• Types of parenchyma cells

  • Chlorenchyma - contain numerous chloroplasts, function in photosynthesis
  • Secretory - dense protoplast, rich in ribosomes, numerous Golgi-bodies, and ER
  • Storage - starch-storing, protein and oil-storing, pigment-storing, crystal-storing, water-storing
  • Transfer - contain cell wall ingrowths, increases surface area of plasma membrane
  • Aerenchyma - have prominent intercellular spaces, common in aquatic/semi-aquatic plants
  • Idioblast - specialized cells that contain certain substances
• Ground tissues


  Tissues composed of parenchyma cells
• Parenchyma cells are ubiquitous because they are found all around the plant
• Origin and distribution of parenchyma cells

  • Ground meristem - pith, pith ray, cortex, mesophyll, and around tissue of reproductive structures
  • Procambium/Vascular cambium - parenchyma cells associated with the primary and secondary vascular tissues
  • Cork cambium - phelloderm
• General structure and appearance of parenchyma cells

  • Polyhedral - many sides, no single pattern of shape, shape varies depending on location/function
  • Isodiametric - around tissues of stem and root
  • Lobed - gymnosperm mesophyll , flower shape
  • Irregular/branched - spongy mesophyll
  • Elongated - prosenchyma of palisade mesophyll
• Cell types of parenchyma

  • Chlorenchyma - cells contain numerous chloroplasts that function in photosynthesis
  • Secretory - dense protoplast, rich in ribosomes, numerous Golgi bodies or developed endoplasmic reticulum
  • Storage cells - starch-storing, protein- and oil-storing, pigment-storing, crystal-storing, water-storing
  • Transfer cells - cells that contain cell wall ingrowths to increase surface area of plasma membrane
  • Aerenchyma - characterized by prominent intercellular spaces
  • Idioblast - specialized cells that contain certain substances
• The relationship of cell shape, size, and specialized parts with the function of the tissue is that they vary because of the cells' respective functions
• Distinguishing characteristics of parenchyma in vascular tissues vs ground tissues

  Vascular: Smaller, thick lignified walls, for transport of food and water

  Ground: Larger, thin walls, compactly arranged, for storage
• General Characteristics of Parenchyma Cells

  1. Living Protoplast - living at maturity

  • can resume meristematic activity and give rise to new cells
  • totipotent
  • Principal seat of essential cellular activities
• General Characteristics of Parenchyma Cells

  2. Thin primary cell wall - important in wound healing, regeneration, formation of adventitious organs, union of grafts

  • no secondary walls
  • primary pit fields are present
• General Characteristics of Parenchyma Cells

  3. Unspecialized morphologically and physiologically - may change functions or combine several different ones
• Are parenchyma cells considered meristematic cells?

  • Yes, if and only if parenchyma cells undergo dedifferentiation to attain its meristematic nature
• Parenchyma is a fundamental tissue

  Foundation of the plant:

  • ontogenetically - reproductive cells (spores and gametes) are parenchymatous in nature
  • phylogenetically - charophytes, other earlier form of plants are parenchymatous in nature
• Parenchyma is a a part of ground tissue

  • it is called ground tissue because it is where the other tissues are embbed