Plant Interactions: 
Plant Anatomy & Secretory Structures


Initial discussion involves Plant:
     1 - body - review
     2 - organs - root, stem, leaf, flower
     3 - tissues and cell types
     4 - cells - emphasis on wall and secretion process
     5 - metabolism - diversity of secondary products

A - Body - review

B - Organs - structure
     1 - root - primary and secondary monocot and dicot
     2 - stem - primary and secondary, monocot and dicot
          lenticels - exchange
     3 - leaf - cell layers, stomates, cuticle
     4 - flowers - parts modified leaves, formation environmental
          cues, structure
          Fertilization - seeds and fruits - dry and fleshy
     5 - seeds - dispersal
 

C - Cell types and tissues
     1 - Parenchyma - thin-walled, potentially meristematic, cortex
            pith, vascular tissues, fruits.
          Wound healing, graft union
     2 - Support
          a - collenchyma - thick primary wall, living
          b - sclerenchyma - thick secondary wall, lignin
               (1) fibers - location
               (2) sclereids - location
     3 - Transport
               (1) xylem - transpiration, cohesion
               (2) phloem - loading source, sink - organic
                    Materials, sucrose, A.A.
     4 - Storage
          a - tannins
          b - carbohydrates
          (1) roots
               (2) stems - potato, parenchyma cells
               (3) waste products - crystals, druse, raphide
 

BASIC STRUCTURE OF LIVING CELLS

     1 - plasma membrane - external boundary of living system
          -invasion must penetrate living system
          a - structure - proteins, phospholipids, channels
          b - selective - carriers, channels
          c - continuity - plasmodesmata, desmotubule
     2 - vacuole - tonoplast.  Water soluble materials -
          alkaloids, pigments, secondary metabolites
     3 - cell wall - rigid
          a - compostion - cellulose, pectins, protein,
          semicelluloses
          b - structure
               (1) middle lamella - pictures, galacturonic
                    acid polymer
                    Selective dissolution - abscission, soft
                    rot (pathogenesis), fruit ripening
               (2) primary wall - secreted by protoplast,
                    Non-living, free diffusion
                    (a) hemicellulose - elastic, heterogeneous
                         polymer - mostly 5c sugars such as
                         arabinose.  Golgi non-cellulosic
                         polysaccharides
                    (b) cellulose - random microfibrils,
                         Synthesis synthetase enzyme rosettes
                         at membrane surface
                    (c)protein - example glycoprotein extensin,
                         high concentration of hydroxy-proline
               (3) secondary wall - fibers, tracheids vessels
                    (a) thick, secreted inside primary wall -
                         S1, S2, S3 - microfibrils at constant
                         direction within lamellum
                    (b) lignin deposited control phenylammonia
                         lyase, no growth.  Function support
                    (c)pits - allow passage materials between
                         cells - simple, bordered
 

PLANT SECRETORY CELLS IMPORTANT IN INTERACTIONS

I - External Secretions
     A - general characteristics
          1 - produced in cytoplasm, move outside or remain
               in cells
          2 - cells have large number of organeles-dictysomes
               produce numerous vesicles.  After ingrowths of
               cell wall and membrane - type of transfer cell
     B - types secretory cells
          1 - glandular trichomes
               a - stalk and head either single or multi-cell
               b - formation - outgrowth of wall of epidermal
                    followed by asymmetric division Head formed
                    by continued mitotic division.  Head covered
                    with cuticle permeable to secretions
               c - many with basal cell(s) suberigid - thought
                    to prevent apoplast movement - plasmodesmata
                    may facilitate symplastic transport
               d - composition - characteristic odor - include
                    volatile oils (peppermint) and resins
                    (tetrahydrocannabinol) Sugar accumulated in
                    certain extrafloral nectaries (groups of
                    glandular trichomes)
                    Stinging nettle - herbivory
     2 - Glands - group of cells which secrete and concentrate materials to the outer surface
          a - types
               (1) salt
               (2) wax
               (3) oil glands - aromatic oils
                    fruit pericarp - orange, lemon
                    floral parts - clove
                    leaves - Eucalyptus
               (4) nectaries - attract pollinating agent
                    location
                    (a) extra-floral
                         Poinsettia, densely packed cells
                    (b) floral mechanism - variety of
                         methods of accumulation -
                         positive hydrostatic pressure
                         result of active process
                         Source - modification of sieve
                         tube solution, selective accumulation
                         of sugars
                         Amount - depends on the physiological
                         state of plant - water, etc.
                         Also, autonomous rhythm corresponding
                         to the periodicity of the pollination
                         control-time, amount

                    (C)  Composition - sucrose primarily, also glucose
                         and fructose - from 25 to 75% as a result of phloem loading,
                         position of flowers,closing in bad weather - protect from rain
                         dilution
                         A.A., lipids, organic acids, phenolics,
                         glycosides, alkalids
                         Some high percentage lipid
                         Highest in A.A. - attract dung flies
                         or carrion flies
                    (d)  Function - pollination but some pseudo-nectaries with no nectar
                         protection
                         Nectar thieves - smaller insects, no
                         pollination
                         Housebreaking - bite, puncture flowers
                    (e)  Interaction Examples -
                        (1) flower aromatic compounds provide
                         signature of the flower - environmental
                         cue to organisms - example pollen eating
                         mites - Colwell studied dispersion -
                         mites exit flower 2-3 seconds to enter
                         hummingbird nostril
                         Sense floral aroma to exit, only 1 of
                         200 mistakes when get off on wrong
                         species
                         (2) Second example - carnivorous plants
                         519 dicot species.  Types have source
                         reduced nitrogen
                         Passive - pitcher plants have numerous
                         secretions
                         (A) wax glands - platelets slippery
                         (B) alluring glands - secrete aromatic
                              compounds and nectar
                         (C)digestive glands - proteases, pass
                              through cuticlular pores
               (f)  Insect adaptations
                    a - mosquito breeds
                    b - spider web at mouth
                    c - immunity
                    Active - Venus fly-trap, bladder wort -
                             Digestive enzymes

II Internal Secretions
     1 - resin ducts - small groups of thin-walled collect
          materials in a central cavity
          cavity origin -
               schizogenous - cell split apart
               lysigenous - cells break down
          Form in response to injury with increased frequency -
          Healing mechanism
               Adaptation - sawfly feed on conifers, store resin,
              larvae use resin emmission as defense mechanism
     2 - laticifers - approximately 20 families, usually
          milky solution (organic acids, carbohydrates,
          alkaloids) and dispersed particles (terpenes,
          resins, rubber)
          Examples:
          (A) Papaya - rich in proteolytic enzyme papain
          (B) poppy - alkaloid opium
          (C)Hevea - rubber latex

          Types
          a - non-articulated - single cells multinucleate,
          growth between cells, some pectinase in latex
          b - articualted - longitudinal files of cells formed
          when end wells break down