EvoDevo Vascular Plants

• Lignin


  Complex polymer of phenolic compounds incorporated in the secondary wall, imparts strength and rigidity to the cell wall
• Secondary cell walls


  Thicker than primary cell walls, contain cellulose, secreted outside of the plasma membrane

  
• Pits


  Holes in the secondary cell wall that allow communication between cells during development and differentiation
• Primary pit fields


  Group of plasmodesmata
• Sclerenchyma


  • Nonconductive cells that have a thick, lignified secondary cell wall (with pits), dead at maturity, two types: fibers and sclereids

  
• Fibers


  Long, very narrow cells with sharply tapering end walls
• Sclereids


  Isodiametric to irregular or branched in shape
• Function of fibers


  • Mechanical support in various organs and tissues
• Function of sclereids


  • Structural support, aid to deter herbivory in some plants
• Collenchyma


  • Live cells with unevenly thickened, pectic-rich, primary cell walls

  
• Tracheary elements


  • Specialized cells that function in water and mineral conduction from the roots to other parts of the plant, elongate cells, dead at maturity, have lignified 2° cell walls, joined end-to-end forming a tubelike continuum

  
• Tracheids


  Imperforate tracheary elements

  
• Vessel members


  Perforate tracheary elements
• Perforation plate


  Contact area of two adjacent vessel members, may be compound or simple, differ in length, width, angle of the end walls, and degree of perforation
• Sieve elements


  • Specialized cells that function in conduction of sugars, elongate cells having only a primary (1°) wall, with no lignified 2° cell wall, semi-alive at maturity, oriented end-to-end forming a tubelike continuum

  
• Callose


  Polysaccharide composed of β-1,3-glucose units
• Sieve plate


  Consist of one or more sieve areas at the end wall junction of two sieve tube members

  
• Types of sieve elements

  • Sieve cells
  • Sieve tube members

  
• Sieve cells


  Have only sieve areas on both end and side walls, ancestral sugar-conducting cells, found in nonflowering vascular plants
• Sieve tube members


  Have both sieve areas and sieve plates, derived from sieve cells, found in flowering plants

  
• Albuminous cells


  Parenchyma cells associated with sieve cells, derived from different parent cells

  
• Companion cells


  Associated with sieve tube members, derived from the same parent cell as are sieve tube members
• Casparian strip


  A band or ring of lignin and suberin that infiltrates the cell wall of endodermal cells, acts as a water-impermeable material that binds to the plasma membrane

  
• Vascular plants


  • Have a haplodiplontic alternation of generations with a dominant, free-living, photosynthetic, relatively persistent sporophyte generation

  
• Sporophytic axes (stems)


  • Branched and have multiple sporangia, referred to as polysporangiophytes, supportive organs bearing elevated leaves and reproductive organs, conductive organs

  
• Stele


  Organization of xylem and phloem
• Protostele


  Central solid cylinder of xylem and phloem
• Cortex


  Largely parenchymatous tissue between the epidermis and vascular tissue
• Sporophytic leaf


  • Dorsiventrally flattened organs for photosynthesis, occur on gametophytes only and are not strictly homologous with the sporophytic leaves of vascular plants, evolution increases the tissue area available for photosynthesis and allows survival in inaccessible habitats

  
• Cuticle


  • Covers the outer cell wall of epidermal cells

  
• Vascular bundles (veins)


  Contain xylem and phloem tissue and conduct water and sugars
• Mesophyll


  Specialized into upper, columnar palisade mesophyll cells and lower, irregularly shaped spongy mesophyll cells

  
• Stomata


  For gas exchange in lower epidermis
• Shoot


  Association of stem plus leaves
• Apical meristem


  Actively dividing cells (continuous mitotic divisions)
• Node


  Point of attachment of a leaf to the stem
• Internode


  Region between two nodes
• Axil


  Tissue at the region of the junction of stem and upper leaf, may begin to divide and differentiate into a bud
• Bud


  Immature shoot system, may develop into a lateral branch or may terminate by developing into a reproductive structure
• Roots


  • Specialized plant organs that function in anchorage and absorption of water and minerals, found in all vascular plants, plants lacking roots generally have uniseriate (one cell thick), filamentous rhizoids