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Secretory Structures
Plant Anatomy 254 Lec 10
Rajaa Abueideh
• Secretion:
- complex phenomena of separation of
substances from the protoplast
- The secreted substances may be
* excess of ions removed in a form of salts,
* excess of products as sugars or cell wall
substances
* end products of metabolism
* products that will not be used physiologically
as alkaloids, tannins, terpens, resins, crystals
* products with special physiological function
as enzymes, hormones
-some secretory substances are waste products
Plant Anatomy 254 Lec 10
Rajaa Abueideh
• The exact role of many secreted
substances is not known.
• No exact distinction between excretion
and secretion although excretion may
refer to removal of substances that are not
used in metabolism.
• Secretion covers both:
- removal of materials from the cell (to
the surface of plant or into internal space)
- Accumulation of secreted substances
in some compartments of the cell.
Plant Anatomy 254 Lec 10
Rajaa Abueideh
Secretory glands are highly specific in their
activities depending on the material they
secrete.
Cytological there are two types of glands:
• Glands that secret hydrophilic substances
[abundance of mitochondria, ER and dictyosomes)
• Glands that secret oil (hydrophobic substances)
[degeneration of the dense protoplast e.g. no
dictyosomes]
Secretion is either by- exocytosis
-diffusion (passive transport)
Plant Anatomy 254 Lec 10
Rajaa Abueideh
• Secretory structures could be
External Secretory Structures (found on surface of
plant)
- Trichomes and Glands
-Nectaries
- Hydathodes
Internal Secretory Structure (embedded in various
tissues)
-Secretory cells
-Secretory cavities and canals
- Laticifers
Plant Anatomy 254 Lec 10
Rajaa Abueideh
• External Secretory Structures
Trichomes and Glands:
-Sometimes part of epidermis is secretory
-Trichomes have unicellular or multicellular
head composed of cells producing the
secretion found on a stalk of non glandular
cells.
- Oil secreting trichomes , oil could be stored
in vesicle in cytoplasm or stored in
plastids.
Plant Anatomy 254 Lec 10
Rajaa Abueideh
• Oil secreting trichomes (mint, geranium,
lavender)
• Stinging hairs in Urtica (nettle plant)
• Trichomes in leaves of insectivorous
secrete mucopolysaccharides to trap
insects and proteolytic enzymes to digest
the insects and the secretion is trapped by
nitrogenous material trapped on the
surface
Plant Anatomy 254 Lec 10
Rajaa Abueideh
Esau,1977
Secretory trichomes
(glandular trichomes)
Plant Anatomy 254 Lec 10
Rajaa Abueideh
• Salt excreting glands (vary in
structure and method of secretion,
carried to gland by transpiration
stream)
- in Atriplex plant bladder like cells
attached to epidermis where ions are
secreted into large central vacuole.,
after cells collapse , ions are
deposited on the surface of the leaf
Plant Anatomy 254 Lec 10
Rajaa Abueideh
Esau, 1977
Salt secreting gland
Plant Anatomy 254 Lec 10
Rajaa Abueideh
- in
Tamarix, complex gland of 8
cells, 6 secretory and 2 are basal
collecting cells, salts accumulate
in microvacuoles until it is
secreted by fusing with plasma
membrane , salts then exit
through pores in the surface layer
Plant Anatomy 254 Lec 10
Rajaa Abueideh
Esau,1977
Plant Anatomy 254 Lec 10
Rajaa Abueideh
• Nectaries
Both xylem and phloem participate in
secretion by nectaris. Vascular tissue
occurs more or less close to the secretory
tissue, some nectaries have their own
vascular bundles, often consisting of
phloem only.
Nectaries secrete sugar-containing liquid
(nectar), the sugar is not as derived from
phloem but modified by enzymes of
nectaries
Plant Anatomy 254 Lec 10
Rajaa Abueideh
• Nectaries could be:
-floral nectaries: occur on flower,
found on sepals or petals, stamens,
ovaries or the receptacles
- Extrafloral nectaries: occur on
vegetative parts of the plant, on
stems, leaves, stipules and pedicle of
flower
Plant Anatomy 254 Lec 10
Rajaa Abueideh
• Nectaries may have the form of glandular
surface or may differentiate into specialized
structures
• The secretory tissue of the nectary may be
restricted to epidermis or may be of several
layers of cells deep.
• The secretory tissue is covered on the outside
with a cuticle
• The secretory cells of nectaries have dense
cytoplasm and small vacuoles often containing
tannins, numerous of mitochondria and ER.
Plant Anatomy 254 Lec 10
Rajaa Abueideh
Esau,1977
Plant Anatomy 254 Lec 10
Rajaa Abueideh
• Hydathodes:
• Secretory structure that discharge water from
the interior of the leaf to the surface (process
called guttation)
• Modified ground and vascular tissue
• Structurally are modified parts of leaves
(modified mesophyll epithem), located at
margins or tips, so water released from xylem
can reach the surface and released through
openings in the epidermis (stomata)
• Epithem is chlorophyll-free parenchyma, may be
compact or with intercellular spaces , may be
differentiate as transfer cells with thick cell wall
Plant Anatomy 254 Lec 10
Rajaa Abueideh
• Hydathods xylem consists of tracheids
• Water released by hydatodes either
passively under the control of root
pressure or secreted actively by
hydathodes cells
Plant Anatomy 254 Lec 10
Rajaa Abueideh
• Internal secretory structures
Secretory cells
Specialized cells (Idioblasts) dispersed
among less specialized cells
secretory cells may be elongate so called
sacs or tubes. could be branched.
Secretory cells are classified based on their
contents, but many secretory cells contains
mixtures of substances
Used in taxonomic purposes of plants. Some
plant families for example have secretory
cells containing oil Rutaceae , others with
resiniferous cells or mucilaginous cells
Plant Anatomy 254 Lec 10
Rajaa Abueideh
• The secretions (oil) are formed in the
thylakoids of plastids, then it appears
in the cytoplasm as droplets, then all
cell components degenerate.
• In many oil cells, the secretion is
found in oil sacs with their own
cellulose wall attached by stalklike
extension to the wall of the cell.
Plant Anatomy 254 Lec 10
Rajaa Abueideh
Plant Anatomy 254
Lec 10
sbs.utexas.edu
Rajaa Abueideh
• Tannin cells are parenchyma cells
• Tannin cells often connected to vascular
bundles.
• It occur in many families in leaves and in pith
and phloem of stems.
• Tannin in tanniferous cells are oxidized to brown
and brown – reddish compounds.
• Crystal- containing cells are parenchyma cells
too .
• cystolith containing cells in Ficus leaves
within epidermal cells attached to the outer
epidermal wall by cellulosic stalk.
• made of calcium carbonate, cellulose and
callose
Plant Anatomy 254 Lec 10
Rajaa Abueideh
Raphide crystals
doctortee.com
biology.uco.edu
Plant Anatomy 254 Lec 10
Rajaa Abueideh
• Raphide crystals are found in
long sac like cells filled with
mucilage, it may be separated
from the living part of
protoplast by cellulosic cell
wall.
Plant Anatomy 254 Lec 10
Rajaa Abueideh
• Secretory cavities and canals:
-are spaces that result from :
- dissolution of cells (lysigenous spaces)
* partly disintegrated cells occur along the periphery of the
cavity
* example oil cavities in citrus plants and mucilage canals
in bud scales of Tilia
- separation of cells from one another
(schizogenous spaces)
* Usually lined with intact cells
• Example Resin ducts in Conifers similar to gum ducts in
dicots
• Resin ducts are long spaces surrounded by resin
secreting cells
• Resin ducts occur in vascular tissues of all plant organ,
Plant Anatomy 254 Lec 10
Rajaa Abueideh
Plant Anatomy 254 Lec 10
Rajaa Abueideh
Plant Anatomy 254 Lec 10
Rajaa Abueideh
• The contents of secretory cavities
and canals are often oily
• Their chemistry is unknown
• Secretory cavities and canals
occur naturally in plants can not
be distinguished from canals and
cavities arising under the stimulus
of injury.
Plant Anatomy 254 Lec 10
Rajaa Abueideh
Laticifers:
• Are series of connected cells that contain latex
(fluid of complex composition)
• Laticifers may be simple or compound by origin:
- Simple laticifers: single cells (nonarticulated
laticifers)
- may become multinucleated if they elongate
and their nuclei divide repeatedly
- Compound laticifers: derived from series of
cells by dissolution of intervening walls so called
(articulated laticifers)
-are multinucleated
Plant Anatomy 254 Lec 10
Rajaa Abueideh
Nonarticulated
laticifers
sbs.utexas.edu
sbs.utexas.edu
Plant Anatomy 254 Lec 10
Rajaa Abueideh
• Both types could be branched or unbranched
• Occur in various tissues and organs but may be
restricted to phloem.
• Laticifers have primary nonlignified cell walls
variable in thickness.
• Laticifers have living protoplast when the latex is
formed but some undergo autolysis during this
process.
• Occur in some families as and certain genera of
families of dicots and monocots
• Euphorbiaceae (Havea souce of rubber)
• Asteraceae (dandelion)
Plant Anatomy 254 Lec 10
Rajaa Abueideh
Latex:
• Secreted by laticifers varies in appearance
and composition
- frequently milky but may be clear and
colorless or brown or orange
- of the components of latex terpenoids (as
rubber), alkaloids (morphine, codeine
papaverine in the opium poppy),
sugars,waxes, proteins, enzymes,
crystals, tannins and starch
Plant Anatomy 254 Lec 10
Rajaa Abueideh