Epidermis

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EPIDERMIS

EPIDERMIS

Outermost layer of cells of organs in primary growthIn most plants, uniseriateM lti i t igi t fMultiseriate– may originate from:a] ground meristem hypodermisb] protoderm multiseriate epidermis

MULTISERIATE EPIDERMIS

Results from periclinal division of protodermOccurs late in ontogenic stageseg. Ficus elasticaMoraceae, certain BegoniaceaeVelamen water storage

CELLS IN THE EPIDERMIS

A] ordinary epidermal cellsB] single cell or groups of cells with special

structure; form or contentC] ll t d ith t tC] cells connected with stomataD] epidermal appendages

A. ORDINARY EPIDERMAL CELLS

Closely attached to form compact layerDevoid of intercellular spacesConifer very thick and lignifiedCutin is present in the outer wall

complex of lipid derivativesdeposition outside the cell forms CUTICLE

layer

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CUTICLE

Present in all parts of herbaceous stem, leavesAbsent in actively growing parts of the rootsThicker plants in dry habitatsTwo layers: 1] cuticle proper (outer; cutin)

2] cuticular layer(inner; cutin+wallmaterials)

Cuticle proper cuticularization (secretion of cutin to the surface of the cell wallCuticular layer cutinization (deposition of cutin between the cellulose microfibrils of the outermost wall layersPectin layerPectin layerEpicuticular wax depostion of wax on the surface of cuticle; granulated or rod-like or continuous layer

gives the “bloom” of many leaves and fruits

WAXaffects the cuticular permeability and the degree to which a surface can be wettedReduces damage to photosynthesis and heat load of leaves

LIGNINRareWhen present, it is found in all walls or only in outer wallEg. Cycadaceae, needles of conifers

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STRUCTURE OF PROTOPLAST OF ORDINARY EPIDERMAL CELLS

Highly vacuolatedContain leucoplastsNumerous mitochondria, ER, spherosomes, di tdictyosomeschloroplastsAnthocyanins –in flowers, in boat of moses

B. EPIDERMAL CELLS WITH SPECIAL STRUCTURE OR CONTENT

In Gramineae: --- long cells and short cells*short cells silica cells and cork cells

--- bulliform cells thin walled and large vacuole- devoid of chloroplasts

lithocysts– Acanthaceae, Moraceae, Urticacaceae, Cucurbitaceae

C. CELLS ASSOCIATED WITH STOMATA

Minute openings or intercellular spaces limited by guard cells– stomataStoma= opening +guard cellsSt t l t l t + Stomatal apparatus or comples = stoma + subsidiary cells

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TYPES OF STOMATA BASED ON ONTOGENY

a. mesogenous-- subsidiary cells (SC) and guard cells common origin

b P igb. Perigenous-- SC develop from protodermal cells adjacent to the stomatal mother cell

c. Mesoperigenous- cells surrounding the stoma are of dual origin

STOMATA

aerial portion of plant; esp. on leavesAbsent in rootsFloating water plants – upper side of leaves

lonlyLand plants – lower surface or bothPlants in full sun environment /high photosynthetic capacity--both

STOMATA

Arrangement> random in plants with reticulate venation> arranged in parallel row with parallel venation

Position relative to other epidermal cell> level> raised> sunken

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Substomatal chamberOpening of stomataShape> kidney shaped> dumb bell shape/ elongated (Gramineae; Cyperaceae)

MAIN TYPES OF STOMATA (EUDICOTS)

Anomocytic (ranunculaceous)Anisocytic (cruciferous)Paracytic (rubiaceous)Diacytic (caryophyllaceous )Actinocytic --uncommon

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MAIN TYPES OF STOMATA (MONOCOT)

1] 4-6 subs. cells2] 4-6 subs. cells; 2 round, smaller than the rest,

situated at the end of guard cell3] G d ll i d l t ll b 2 3] Guard cells are accompanied laterally by 2

subs. Cells4] guard cells are not assoc. with any subs. cells

ONTOGENY OF STOMATA

TYPES OF STOMATA DEVELOPMENT (BASED ON ORDER OF APPEARANCE OF STOMATA)

Basipetal – parallel venation--from the tip of the organ to its baseNo pattern– reticulation venation

STOMATA FREE REGIONS

inhibition of additional stomata by already differentiated onesFormation of stomata together with the surrounding cells as part of the same surrounding cells as part of the same developmental patternInduction of stomata pattern by the pattern of the underlying tissue (mesophyll)

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D. EPIDERMAL APPENDAGES

Unicelluar and multicellular-- TrichomeMassive structures such as warts, prickles (epidermal and subepidermal)– emergencesTRICHOMES b lig ifi d ith d TRICHOMES—may be lignified, with secondary wall or lose their protoplast-- has taxonomic implications

TRICHOMES

1. Non-glandular a. simiple unicelluar or multicellular, uniseriate, non-flattened hairsb if h i fl t d lti ll lb. squamiform hairs—flat and multicellular*sessile scale*stalked peltate*dendritic

c. multicellular hairs– stellate; branched candelabrum-liked. T-shaped hairs

TRICHOMES

2. Glandular- secretion of various substances (salt, sugar as in nectar, lipids, gums)-possess endodermal cells (prevents backflow)possess endodermal cells (prevents backflow)- sessile or stalked

a. salt-secreting trichomesb. Trichome-hydathodec. nectar-secreting

d. Mucilage secretinge. Glands of carnivorous plantsf. Trichomes secreting lipophilic materialsg. colleters- secreting sticky substancesh. Stinging hairs

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3. Root hairs- tubular elongations of epidermal cells- appear beyond the meristematic region

i bl f h t i d- viable for a short period