2. Secretory structures
ecretion the release of substances that have a
S –
special physiologic function (enzymes, hormones)
xcretion‐ separation of products eliminated
E
from metabolism
Secretion is used to include excretion :
 role of many of these substances is not known
 they may be found in the same container
 Secretion may remain in the cell producing it
as droplets , be walled off from the cytoplasm
or leave the cell

3. Types of secretory structures
xternal secretory structures
E
 A. Trichome and glands
 B. Nectaries
 C. Osmophors
 D. Hydathodes
nternal secretory structures
I
 A. Secretory cells
 B. Secretory spaces
 C. Laticifers

4. Types of secretory structures
xternal secretory structures
E
 A. Trichome and glands
 B. Nectaries
 C. Osmophors
 D. Hydathodes
nternal secretory structures
I
 A. Secretory cells
 B. Secretory spaces
 C. Laticifers

5. Trichomes and glands
 trichomes simpler than glands although no sharp
distinction exists between glandular hairs and glands
 Trichomes
 Contains anti‐herbivore secretions
 Glands
 Salt glands‐ mechanism for the plant to get rid of excess salt
absorbed from the environment
 Function of plants living in salt marshes and salt infiltrated
soils in coastal marine areas
 Glands of insectivorous plants‐secrete digestive juices

6. Glandular hair of
Urtica dioica
(stinging nettle)
‐Upon contact with an
animal, the tip breaks off
releasing the toxic substances
in the cell as it penetrates the
skin.
‐ Reported to contain a
histamine and an
acetylcholine

7. Salt gland of
Tamarix aphylla
Note that the gland, which
consists of two basal
collecting cells and four
secretory cells, is sunken in
the epidermis. Salt is
transferred symplastically
from the leaf mesophyll into
collecting cells and secretory
cells and apoplastically
through the wall labyrinth to
the exterior

9. tructure of secretory cells
S
 Have dense protoplast
 Large nucleus
echanisms for release
M
 1. May release secretion in between wall and
cuticle
 A. Eventually cuticle bursts (may regenerate
cuticle or dry up after excretion)
 B. Or not at all but individual cells are severed
after release of secretion
 2.Special mechanism (tip breaks off and
contents e.g. histamine escape into wound)

11. Glandular
trichome

12. Glandular hair of
Urtica dioica
(stinging nettle)
‐Upon contact with an
animal, the tip breaks off
releasing the toxic substances
in the cell as it penetrates the
skin.
‐ Reported to contain a
histamine and an
acetylcholine

13. Nectaries
May occur on flowers (floral nectaries) or
vegetative parts (extrafloral nectaries)
 Secretory tissue
 restricted to the epidermal layer or may
include subsurface layers
 have dense cytoplasm
 may be papillate
 are closely packed
 have thin walls

15. Nectaries
 Sugars of nectaries derived from phloem
 Nectar excreted through
 cell wall and ruptured cuticle
 or through stomates (that are not able to
close and open)

16. Osmophors
 scent of the flowers produced by essential oils
 originates from epidermis of perianth or from
osmophors (special glands)
 osmophors found in Aristolochiaceae, Araceae etc.
 floral parts differentiated as osmophors may
assume the form of flaps, brushes or cilia
 may be distinguished by using neutral red

17. Method to
locate
osmophors

18. Secretory
tissue of
osmophors
Emission of volatile
secretion is of short
duration and is associated
with utilization of large
a m o u n t s o f s to ra ge
products

19. Hydathodes
 A structure that discharge water from the interior
of the leaf to the surface
 water contains dissolved salts, sugars and other
organic substances
 Eliminates water through the terminal tracheid
 in contact with epithem
 may have no epithem and water moves through
ordinary mesophyll

20. Guttation, the exudation of water droplets
Occurs when water absorption > loss of water

21. hydathode

22. Internal secretory structures
ecretory cells
S
 Crystal‐ containing cells may die after
deposition of the crystal or may be separated
from living part of the protoplast
ecretory spaces
S
 In the form of spaces or cavities formed by
schizogeny, lysigeny or their combination
 Epithelial cells of resin canals
 Lysigenous space

23. Secretory cells

24. Secretory cells
A. Cells containing tannins
B. Oil idioblast

25. Secretory
spaces
A‐D. Schizogenous
cavities
E. Lysigenous
cavity

26. Internal secretory structures
aticifers
L
 Derived from the word latex meaning juice in
Latin
 Because of the milky appearance of the latex, it
is sometimes called lactiferous cells or vessels
from the Latin word for milk, lac

27. aticifers
L
 According to origin:
 1. Simple laticifer – derived from a single cell
 2. Compound laticifer – derived from union of
cells
 According to structure:
 1. Articulated laticifer ‐ (laticiferous vessel)
compound in origin consists chains of cells
end walls may remain, become perforated or
are completely removed

28. aticifers
L
 According to structure:
 1. Types:
Articulated nonanastomosing‐ compound
tubes not connected with each other laterally
(Ipomoea, Convolvulus, Achras sapota, Allium,
Musa)
Articulated anastomosing ‐ cell chains
connected with each other laterally (Hevea,
Lactuca, Carica papaya, Manihot)

29. Laticifers in Allium
sativum

30. laticifers

31. aticifers
L
 According to structure:
 Nonarticulated laticifer‐ (laticiferous cell)
simple in origin
through continued growth develops into a
tube‐like structure
 Types:
Nonarticulated unbranched – develop more or
less straight tubes (Vinca, Urtica, Cannabis)
Nonarticulated branched – each cell forms
branch repeatedly forming an immense
system of tubes (Nerium, Ficus, Euphorbia)

32. aticifers
L
 Composition and physical state of
latex
 Liquid matrix with minute organic suspension
Matrix contain: carbohydrates, organic acids,
salts, alkaloids, sterols, fats, tannins, and
mucilages
The dispersed particles: terpenes i.e.,
essential oils, balsams, resins, camphors,
carotenoids and rubber
 Latex may be clear or milky
 Flow of latex in when cut open is a pressure
flow

33. Composition
of laticifers
Latex with numerous
vesicles ; contain
polyterpenes and other
compounds

34. aticifers
L
 Cytology
 With living protoplast retaining nucleus at
functional maturity
 Cytoplasm along the periphery surrounding
the vacuolar sap
 In nonarticulated form of many plants, the
nuclei undergo divisions resulting in a
multinucleate coenocytic condition

35. aticifers
L
 Cytology
 if multinucleate in articulated forms, it is due
to fusion of protoplasts
 the latex particles are formed in the cytoplasm
 the tonoplast breaksdown in mature laticifers;
the latex particles escape into the vacuolar sap
which become part of the latex

36. aticifers
L
 Structure of the wall
 nonlignified and plastic
 Development
 Nonarticulated laticifers
A. Branched
o Arise when the cotyledons are initiated in
the form of relatively few primordia
o grow concomitantly with the plant into
branched systems permeating the whole
plant body

37. Nonarticulated
laticifer of nerium
oleander
(development)

38. aticifers
L
 Development
 Nonarticulated laticifers
B. Unbranched – primordia seen in
developing shoot (Vinca, Cannabis) or in the
shoot and root and new primordia arise
repeatedly beneath the apical meristem by a
combination of intrusive growth and
symplastic growth

39. aticifers
L
 Development
 Articulated laticifers
A. anastomosing
o develops into extensive tube‐like structures,
by constant addition of new primordia to
the existing ones
o in the hypocotyls and the cotyledons of the
embryo in the mature seed
o end walls of primordia are intact but during
germination break down and the cell rows
are converted into vessels

40. aticifers
L
 Development
 Articulated laticifers
A. anastomosing
o the vessels are extended by differentiation of
further meristematic cells into laticiferous
elements in acropetal direction
o where the vessels lie side by side, parts of the
common wall become resorbed; if they are
further apart, the intervening cells may become
changed into laticiferous cells with resorption
of common walls; some of the anastomoses
may end up blindly
o in the secondary phloem may develop from
derivatives of fusiform initials

41. aticifers
L
 Development
 Articulated laticifers
B. nonanastomosing
o the development of nonanastomosing kind
is similar to anastomosing laticifers, except
that no lateral connections are established
among the various tubes

42. Articulated laticifer development

43. aticifers
L
 Arrangement in the plant
 frequently distributed generally through the
plant
 sometimes are restricted to certain tissues
most commonly the phloem
may occur also in the xylem (Caricaceae)
cortex (Musa)
pericycle
mesophyll

44. Arrangement of laticifers in the
plant

45. aticifers
L
 Possible function
 Vital sap vessels like blood vessels of animals
 Take part in the translocation of assimilates
 Take part in the storage of food materials
 They form an excretory system
 Protection as the latex may play a role in:
covering wounds
as defense against herbivores and
microorganisms