1/13/2010

1

Secretion –the release of substances that have a special physiologic function (enzymes hormones)(enzymes, hormones)

Excretion- separation of products eliminated from metabolism

Secretion : A] may remain in the cell producing it as

droplets

B] walled off from the cytoplasm

C] may leave the cell

External secretory structuresA. Trichome and glandsB. NectariesC. OsmophorespD. Hydathodes

Internal secretory structuresA.Secretory cellB. Secretory spacesC. Laticifers

1/13/2010

2

Trichomes may release Terpenes (essential oils)Sugars (floral and extrafloral nectaries)Sugars (floral and extrafloral nectaries)Water (trichomatous hydathodes)Salts (plants in saline habitats)

Glands may release- Nectar- mucilagesdigestive enzymes (insectivorous plants)-digestive enzymes (insectivorous plants)

Structure of secretory cells• Have dense protoplast, large nucleus

Mechanisms for release1.may release secretion in between wall and cuticle

* Eventually cuticle bursts (may regenerate cuticle or Eventually cuticle bursts (may regenerate cuticle or dry up after excetion)

* Or not at all but individual cells are severed

2.special mechanism (tip breaks off and contents e.g. histamine escape into wound

May occur on flowers (floral nectaries) or vegetative parts (extrafloral nectaries)

epidermal layer or may include subsurface layers,

have dense cytoplasm may be papillate are have dense cytoplasm, may be papillate, are closely packed and have thin walls

Sugars of nectaries derived from phloem

Nectar excreted through A. cell wall and ruptured cuticle B. through stomates

(that are not able to close and open)

scent of the flowers produced by essential oils

Originate from epidermis of perianth or from osmophores (special glands)

Aristolochiaceae Araceae etcAristolochiaceae, Araceae etc.

form of flaps, brushes or cilia

Emission of volatile secretion is of short duration and is associated with utilization of large amounts of storage products

1/13/2010

3

A structure that discharge water from the interior of the leaf to the surface

Eliminates water through the terminal tracheid in contact with epithemtracheid in contact with epithem

EPITHEMthin walled parenchyma deficient in

chloroplasts and provided with intercellular spaces through which water moves through the incompletely differentiated stomata

A. Secretory cells(crystal containing cells may die after deposition of the crystal or may be separated from living part of the protoplast)

B. Secretory spacesIn the form of spaces or cavities formed by schizogeny, lysigeny or their combination

Epithelial cells of resin canals(excretion found in protoplast next to wall facing the space)

Lysigenous space (oil cavities –Citrus)(excretion occurs first in intact cells before the

latter breakdown)

1/13/2010

4

Derived from the word latex meaning juice in latin

Because of the milky appearance of the Because of the milky appearance of the latex, it is sometimes called lactiferous cells or vessels from the latin word for milk, lac

According to origin:1. Simple laticifer – derived from a single

cell2 Compound laticifer derived from 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 end walls may remain, become perforated or are completely removed

2. Nonarticulated laticifer- (laticiferous cell) simple in origin which through continued growth develops into a tube-like structure

Articulated nonanastomosing-compound tubes not connected with each other laterally (Ipomoea, convolvulus Achras sapota Allium musa)convolvulus, Achras sapota, Allium, musa)

Articulated anastomosing –cell chains connected with each other laterally (Hevea, Lactuca, Carica papaya, Manihot)

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

1/13/2010

5

Liquid matrix with minute organic suspensioncontain: carbohydrates, organic acids, salts, alkaloids, sterols, fats, tannins, and mucilagesmucilagesThe dispersed particles: terpenes which include essential oils, balsams, resins, camphors, carotenoids and rubberLatex may be clear or milkyFlow of latex in when cut open is a pressure flow

1/13/2010

6

With living protoplast retaining nucleus at functional maturity

Cytoplasm along the periphery surrounding the vacuolar sap

nonarticulated coenocytic condition; if similarly observed nonarticulated - coenocytic condition; if similarly observed in articulated forms, it is due to fusion of protoplasts

The latex particles are formed in the cytoplasm

no clear demarcation bet. the cytoplasm and vacuole

the tonoplast breakdown the escape of the latex particles into the vacuolar sap which become part of the latex

Structure of the wallWalls of laticifers are nonlignified and

plasticArrangement in the plantArrangement in the plant

generally through the plantmost commonly the phloemmay occur also in the xylem

(Caricaceae), cortex (Musa), pericycle, mesophyll

Vital sap vessels

Take part in the translocation of assimilates-association with the vascular bundles

storage of food materials but not readily mobilized during unfavorable conditions

form an excretory system

Protection--seals wounds, as defense against herbivores and microorganisms