Epidermis

• 1. Apical meristem
  2. Protoderm
  3. Epidermis
  4. Cork cambium
  5. Cork
  6. Phelloderm
  7. Procambium
  8. Primary phloem
  9. Primary xylem 
  10. Fascicular cambium
  11. Vascular cambium
  12. Secondary xylem
  13. Secondary phloem
  14. Cork cambium
  15. Ground meristem
  16. Pith
  17. Cortex
  18. Interfascicular cambium
  19. Cork cambium

  
• Epidermis is derived from the Greek words:

  • epi meaning upon
  • derma meaning skin
• Epidermis

  • outermost layer of cells on all parts of the primary plant body
  • usually one layer
  • epidermal tissues develop from the protoderm 
  • localized externally
  • rhizodermis: epidermis of the root

  
• Is the epidermis present in all parts of the plant body? 

  • absent in the root cap 
  • not differentiated in the apical meristems
• Shoot Epidermis

  • outermost cell layer of the apical meristem
• Root Epidermis

  • has a different origin from the shoot epidermis
  • rhizodermis/epiblem 
  • Dermatocalyptrogen
  • Cuticle is absent or very thin 
  • Root hairs from trichoblast which function in increasing absorption of the roots
• Where do the epidermal tissues of angiosperms develop from?

  • outermost layer of SAM, dermatogen
  • Tunica (Tunica-Corpus Theory)
  • Dermatogen (Histogen Theory)
• Where do the epidermal tissues of gymnosperms develop from?

  • lateral derivatives of apical initials
  • Cytohistological Theory
• Where do the epidermal tissues of pteridophytes develop from?

  • common origin with deeper lying tissues
  • Apical Cell Theory
• Epidermis in different types of plants:

  • Plants with little or no secondary growth: epidermis is retained in plants with little or no secondary growth
  • Monocots: replaced by a special type of periderm
  • Woody plants (stem/root): replaced by periderm
  • Plants that have undergone secondary growth: epidermis may still be present in plants that have undergone secondary growth
• In such instance, how does the plant body accommodate its increase in girth?  

  • Meristematic tissues which enables plants to support growth and form bark

  • vascular cambium - secondary xylem and secondary phloem
  • cork cambium - generate cork cells
• Characteristics:

  • The epidermis is the outermost layer of the plant parts in the plant body 
  • The epidermis is a complex tissue composed of wide variety of cell types which work together as a unit
  • Epidermal cells have living protoplasts at maturity 
  • Epidermal cells are tightly joined together with no intercellular spaces 
  • Epidermis is typically uniseriate (In some leaves, the protodermal cells and their derivatives divide periclinally, resulting to a multiseriate epidermis)
  • Cuticle may be present on the epidermis of the aerial parts of the plant

  
• Velamen

  • seen in aerial roots of orchids and palms and some leaves (formed late in development)
  • specifically in, Ficus, Peperomia, Begoniaceae, and Malvaceae 
  • multiple epidermis 

  
• What is the significance of the velamen? 

  • provides support, prevent water loss and assist in absorption
• Some plants have epidermal-looking tissue layers known as the hypodermis. Can this be considered as a dermal tissue?

  • Hypodermis: resembles a multiseriate epidermis, and is found right next (below) the true  epidermis
  • derived from the ground meristem
• Functions:

  • reduction of water loss by transpiration (cuticle)
  • mechanical protection (no intercellular spaces/compact arrangement)
  • gaseous exchange through stomata 
  • offers mechanical support and stiffness to stems (compact arrangement/cuticle covering)
  • dynamic storage of  the compartment of various metabolic products (inside of cells)
• Functions:

  • site of perception involved in circadian leaf movements and photoperiodic induction (presence of chloroplast) 
  • site of photosynthesis in plants submerged in water
  • protects the mesophyll from damage that may cause by radiation (cuticle)
  • acts as lenses (cuticle)
  • absorption of water and solute both in the shoot and root 
  • Protection from injury 
• Structural Components of the Epidermis 

  1. Ordinary Epidermal Cells or Pavement Cells 

  • typically tabular/rectangular in shape  
  • many have wavy anticlinal walls 
  • varied shapes in surface view
  • living protoplasts at maturity (have functional chloroplasts and protein crystals vacuoles with high amount of water and anthocyanins)
  • wall vary in thickness (due to the presence of cuticle)
• Ordinary Epidermal Cells or Pavement Cells 

  Other cell wall features:

  • Pectin Layer is continuous with the middle lamella and bonds the cuticle to the outer walls
  • Teichodes are channels along the outer wall that functions in foliar absorption and excretion

  * plasmodesmata in outer walls of epidermal cells
• Structural Components of the Epidermis 

  2. Stomata

  • Openings in the epidermis, each bounded by a pair of guard cells 
  • Regulate exchange of water vapor and of CO2 
  • Distribution and abundance is affected by light and CO2 
• In which parts of the plant body can the stomata be found? 

  • it is found in all aerial parts of the primary plant body most abundant in leaves, rarely found in roots
• Classification of occurrence of stomata in leaves:

  Amphistomatic 

  • found on both surfaces; adaxial and abaxial surface
  • most monocots

  Epistomatic 

  • found in the upper epidermis; adaxial surface
  • plants submerged in water

  Hypostomatic 

  • found in the lower epidermis
  • eudicots

  
• Classification based on level of their position in the epidermis:

  On the same level - as adjacent epidermal cells; unspecialized for any environments

  Raised - above the surface of the epidermis; found in areas with a lot of water present to prevent taking too much water

  Sunken - below the surface of the epidermis

  On stomatal crypt - restricted to depressions/ invaginations (stomatal crypts) often contain trichomes

  
• What is the significance of stomatal crypts?

  • increase air boundary layer
  • less water loss
  • to prevent dessication or drying of trichomes
• Components and other related cells

  1. Guard Cells 

  • Pair of specialized epidermal cells that are distinguished from the pavement cells by their green color and unique shape 
  • Eudicots have crescent-shaped guard cells while monocots have dumbbell-shaped guard cells. 
  • Lined by cuticle 
  • Have prominent nucleus, numerous mitochondria and poorly developed chloroplasts  
  • Chemicals/ions involve in closing and opening of the stomatal pore 
• Stomatal Development

  1. starts from asymmetric division of protodermal 
  2. cell cell with shorter, densely staining cytoplasm, and large nucleus will be the precursor, stomatal meristemoid  
  3. equal division gives rise to the guard cells 
• 2. Subsidiary Cells 

  • Border the guard cells 
  • Differ in size, shape, arrangement, and sometimes in content from ordinary epidermal cells  
  • Arise from guard mother cell or other protodermal cell 

  1. Mesogenous origin - all subsidiary and neighboring cells arise from where the guard cells originated  
  2. Perogenous Origin - none of the subsidiary or neighboring cells have a common origin with the guard cells
  3. Mesoperigenous - if one subsidiary or neighboring cell is directly related ontogenetically with the guard cells; the others are not
• Ledge - Cuticular, play a role in regulating water vapor loss

  Substomatal Chamber - Connects the intercellular air spaces of the mesophyll
• Types of the configuration of stomatal complexes: 

  • Floating - a single subsidiary cell surrounds the guard cell pair
  • Anomocytic - subsidiary cells are lacking
  • Anisocytic - guard cells are surrounded by 3 subsidiary cells, with one cell, smaller than the other two
  • Paracytic - stomata is accompanied by two subsidiary cells that is parallel to the long axis of the guard cells
  • Diacytic - stomata is enclosed by a pair of subsidiary cells whose common walls are at right angles with the guard cells
• Types of the configuration of stomatal complexes: 

  • Actinocytic - stomata is surrounded by a circle of radiating cells whose long axes are perpendicular to the outline of the guard cells
  • Cyclocytic (encyclocytic) - stomata is surrounded by one or two narrow rings  of subsidiary cells, numbering four or more
  • Tetracytic - stomata is enclosed by four subsidiary cells, two lateral and two polar (terminal), also found in many monocots
  • Triacytic - three subsidiary cells adjoin the guard cell pair
  • Graminaceous - guard cells are dumbbell shaped and subsidiary cells lie parallel in a paracytic fashion
• 3. Trichomes

  • Highly variable appendages arising from protuberances from an epidermal cell 

  Functions of Trichomes:

  • reduction of transpiration rate 
  • absorption of water and minerals 
  • salt secretion 
  • protection against UV-B radiation damage 
  • defense against insect 
• How do trichomes reduce transpiration rates?

  • By increasing the reflection of solar radiation and the boundary air layer
• Morphological Categories Classification of Trichomes: 

  • Papillae 
  • simple (unbranched) 
  • 2-5 armed trichomes 
  • stellate 
  • scale or peltate  
  • dendritic (branched) 
  • root hairs 
• Classification Based On Specialization of Trichomes: 

  • Stinging 
  • pearl gland 
  • cystolith-containing hairs 
  • water vesicles
• 4. Other Specialized Cells

  
  

  Silica cells and Cork cells 

  • Provides support to the leaves 
  • Increases resistance to various insects and pathogens

  Bulliform Cells 

  • Large, thin-walled, highly vacuolated 
  • Function in the rolling or unrolling of leaves following the loss of uptake of water

  Cystolith 

  • Contains calcium carbonate, silica 
  • Physiological significance is unclear
• Identify the following:

  1. Subsidiary cells
  2. Guard cells

  
• Identify the following:

  1. Ledge
  2. Cuticle
  3. Substomatal chamber

  
• Identify the stomatal complex:

  Anomocytic

  
• Identify the stomatal complex:

  Anisocytic

  
• Identify the stomatal complex:

  Diacytic