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Epidermis Plant Anatomy 254 lec 5 nsci.plu.edu plant Anatomy 254 lec.5 RajaaAbueideh Abueideh Rajaa • The epidermis is a system of cells. • Vary in structure and function. • Form the covering of the primary plant body.( the layer of cells in contact with the external environment of the plant) • It may last through the life of a given plant part or it may be replaced by other protective tissue (periderm) plant Anatomy 254 lec.5 Rajaa Abueideh • It is usually one layer of cells in thickness. • Sometimes the protoderm (meristems that will differentiate into epidermis) divide parallel (periclinally X anticlinally)with the surface and their derivatives may divide again resulting in tissue with many related layers (multiple epidermis) (in leaves, velamen: multiple epidermis covering aerial roots in epiphytic plants) plant Anatomy 254 lec.5 Rajaa Abueideh velamen layers of dead, hollow cells sta.uwi.edu plant Anatomy 254 lec.5 Rajaa Abueideh sbs.utexas.edu plant Anatomy 254 lec.5 doctortee.com Rajaa Abueideh • Multiple epidermis (multiseriate epidermis) in leaves the outermost layer has epidermal characteristics where as those beneath developed into a tissue with few or no chloroplasts. May function in water storage Sometimes subepidermal layers resemble the multiple epidermis but derived from ground tissue so to differentiae between subepidermal layers and epidermis is by developmental studies. plant Anatomy 254 lec.5 Rajaa Abueideh • Function of epidermis: • Restricts transpiration (contains cutin (fatty material) within outer wall and on its surface (cuticle)) • Gas exchange (presence of stomata) • Mechanical support (compact arrangement of cells and presence of tough cuticle layer) • Absorption ( thin walled and presence of root hairs) • Water storage (xerophytic plants) • Site of light perception involved in circadian leaf movement and photoperiodic induction plant Anatomy 254 lec.5 Rajaa Abueideh nature-education.org plant Anatomy 254 lec.5 Rajaa Abueideh • Shape & Composition of Epidermis: • Unspecialized cells + specialized cells • Most of epidermal cells are tubular. In elongated plant parts as stems, petioles, vein ribs of leaves, leaves of monocots the epidermal cells are elongated parallel with the long axis of plant part. In leaves, petals, ovaries and ovules the epidermis may have wavy vertical walls plant Anatomy 254 lec.5 Rajaa Abueideh Epidermis in stems Epidermis in leaves sbs.utexas.edu sbs.utexas.edu plant Anatomy 254 lec.5 Rajaa Abueideh • Epidermal cells have living protoplasts. • May store products of metabolism. • They contain plastids with few grana so are deficient in chlorophyll (epidermis of plants of shady habitats contains photosynthetically active chloroplasts) plastids may contain starch (amyloplasts, also chromoplasts may present) protein and crystals. • Vacuoles may contain anthocyanin plant Anatomy 254 lec.5 Rajaa Abueideh • Specialized epidermal cells: Guard cells Subsidiary cells Trichomes (epidermal appendages) Idioblasts = cells in a tissue that differ in size, form or contents from cells of the tissue) (cells containing tannins, oils, crystals and other substances: silica cells , cork cells) Bullliform cells (in monocot leaves) elongated bubble like cells Sclerenchyma may present (sclereids or fibers) Secretory cells in some plants plant Anatomy 254 lec.5 Rajaa Abueideh biologie.uni-hamburg.de botany.hawaii.edu waynesword.palomar.edu plant Anatomy 254 lec.5 Rajaa Abueideh chemeng.ntnu.no plant Anatomy 254 lec.5 Rajaa Abueideh • Development of epidermis : • Epidermis differentiates from meristematic surface layer (protoderm or dermatogen) by periclinal division in the developing embryo. plant Anatomy 254 lec.5 Rajaa Abueideh Mature epidermis retains it potential for growth for long time. - in perennial stems form periderm in late life or not at all, the epidermis continues to divide (anticlinal Division: at right angle to the surface) in response to increase in stem width and when periderm is formed the source of meristematic phellogen may be the epidermis - the adventitious buds arise from epidermis. plant Anatomy 254 lec.5 Rajaa Abueideh • The cell wall of epidermal cell: - Varies in thickness in different plants and in different parts of the same plant. - In thin walled epidermis the outer wall is the thickest - thick walled epidermis is found in leaves of conifers, the thick wall probably secondary , lignified - The thick wall may be silicified as in grasses - Primary pits and plasmodesmata present. plant Anatomy 254 lec.5 Rajaa Abueideh Thick walled epidermis in leaves of conifers facultyweb.berry.edu plant Anatomy 254 lec.5 Rajaa Abueideh • The epidermal wall contains wall fatty substance cutin • Cutin occurs: (stained using sudan IV dye) – within the wall between cellulose micells. - as separate layer the cuticle on the outer surface of the epidermis, that varies in thickness and its development depending on environmental conditions Cutininization: the process of impregnation with cutin Cutilicularization: the formation of cuticle plant Anatomy 254 lec.5 Rajaa Abueideh • Cuticle is found in all plant surfaces exposed to the air, but sometimes present in the absorbing region of the root. Even the root hairs • Cuticle is covered with wax either: - in smooth flat-lying form - as rods or filaments growing from the surface (epicuticular waxes) • The composition of cuticle and cutinized wall is complex (cellulose, pectic compounds, cutin, waxes and other substance) plant Anatomy 254 lec.5 Rajaa Abueideh plant Anatomy 254 lec.5 Rajaa Abueideh • A depression in the cuticle over the aticlinal wall where the wax layers are thinner, so water loss and materials uptake occur easily there (common in epidermis of leaves) • Cutin and waxes are synthesized in living protoplasts and migrate to the surface through the cell wall. • Sometimes cuticular layers are formed in cortical cells for protection (cuticular epithelium) • In some roots the epidermis is worn away by friction with soil particles so it is replaced by exodermis (sclerenchyma) plant Anatomy 254 lec.5 Rajaa Abueideh lipidlibrary.aocs.org plant Anatomy 254 lec.5 Rajaa Abueideh Stomata • Stomata are openings (pores or apertures) in the epidermis. • For gaseous exchange (water released, CO2 uptake) • Occur on most plant surfaces above ground especially on green photosynthetic stems and leaves and on floral parts. plant Anatomy 254 lec.5 Rajaa Abueideh Guard cell may be covered with wax emc.maricopa.edu plant Anatomy 254 lec.5 Rajaa Abueideh agritech.tnau.ac.in • Stomata varies on different parts of the same leaf and on different leaves on same plant. It is affected by environmental conditions • In leaves it may occur on both sides or only on one side which is usually the lower one. • Vary depending on their position relative to epidermis could be : -even with other epidermal cells - raised above - below the surface of epidermal cells (sunken stomata as in gymnosperms) plant Anatomy 254 lec.5 Rajaa Abueideh Raised stomata biologie.uni-hamburg.de plant Anatomy 254 lec.5 botany.hawaii.edu Rajaa Abueideh • Bound by two specialized epidermal cells (guard cells) that change in shape to open or close the stomata.(wall away from pore is thicker than the other, [k+] increase, starch consumed during opening of pore) ( stoma: the pore and two guard cells) Guard cells have nuclei and chloroplasts that accumulate starch • Guard cells (as seen from the surface)are either: kidney shaped (in most plants) cuticle covering these cells extends over surface facing stomatal pore and substomatal cavity. or dumbbell-shaped (some monocot plants as Poaceae and Cyperaceae) The two guard cells are interconnected through pores in the bulbous ends of those guard cells plant Anatomy 254 lec.5 Rajaa Abueideh tutorvista.com plant Anatomy 254 lec.5 Rajaasparknotes.com Abueideh plant Anatomy 254 lec.5 Rajaa Abueideh mrothery.co.uk • Stomata may be surrounded by cells that differ in shape and in contents (sometimes) from ordinary epidermal cells (subsidiary cells) which participate in osmotic changes involved in movements of guard cells. plant Anatomy 254 lec.5 Rajaa Abueideh lima.ohio-state.edu plant Anatomy 254 lec.5 Rajaa Abueideh cccmkc.edu.hk plant Anatomy 254 lec.5 Rajaa Abueideh • Development of guard cells and stomata :guard cells results from unequal division of the protodermal cells results in formation of short cells and long cells, guard cells results from short cells (larger nuclei, nucleoli, simple plastids, more enzymes, more nucleohistones, proteins ,DNA and RNA) • The stomata occur when the intercellular space between the guard cells swells and the connection between the cells is weakened so separate forming the pore. plant Anatomy 254 lec.5 Rajaa Abueideh Undifferentiated epidermal cell Protodermal cell Larger daughter cell Guard mother cell faculty.washington.edu plant Anatomy 254 lec.5 Rajaa Abueideh • Development of subsidiary cells: Subsidiary cells may arise from the same precursor as the stoma or from other cells. There are three stomatal types depending on ontogeny (development, differentiation and growth) During development, a protodermal cell undergoes un equal mitotic division to produce larger daughter cell and meristemoid (guard cell mother cell) plant Anatomy 254 lec.5 Rajaa Abueideh Ontogenetic stomatal types:(types of stomata based on development of subsidiary cells) 1- agenous: the meristemoid give rise directly to guard cells and no subsidiary cells 2- mesogenous: the meristemoid cell gives rise to guard cells and subsidiary cells by several mitotic divisions 3- perigenous: the meristemoid give rise to guard cells and subsidiary cells formed from neighboring cells plant Anatomy 254 lec.5 Rajaa Abueideh • Types of stomata based on arrangement of mature subsidiary cells: The same species may show more than one type of stomata. 1- Anomocytic (irregular celled): stomata lack subsidiary cells 2- Anisocytic (unequal celled): stomata with three unequal subsidiary cells (one smaller than the other two) 3- Diacytic (cross celled): stomata with one pair or more than one pair of subsidiary cells with their common wall at right angles to guard cells 4- Paracytic (parallel celled): stomata have one or more subsidiary cells at either side of the guard cells 5- Actinocytic (radiate celled): several subsidiary cells with perpendicular longitudinal axes to outline of the guard cells. plant Anatomy 254 lec.5 Rajaa Abueideh plant Anatomy 254 lec.5 cognosy4all.blogspot.com Rajaa Abueideh miosjournal.org Diacytic stomata avin2000.persiangig.com Paracytic stomata Actinocytic stomata plant Anatomy 254 lec.5 Rajaa Abueideh beyondthehumaneye.blogspot.com Anomocytic stomata .flickr.com plant Anatomy 254 lec.5 Rajaa Abueideh Anisocytic stomata plant Anatomy 254 lec.5 Rajaa Abueideh miosjournal.org Trichomes • Are variable appendages of the epidermis. • Vary widely in form and function . • Could be glandular and non glandular hairs, stinging hairs,scales, papillae and root hairs • Could be unicellular or multicellular, branched or unbranched • Occur on all parts of the plant surface • May persist through the life of a plant or may fall off early. • Some of the hairs remain alive , others die and become dry. • May be used for taxonomic purposes. plant Anatomy 254 lec.5 Rajaa Abueideh • Their function: - Can insulate the mesophyll from excessive heat - May serve to remove salts from the leaf tissue so prevent the accumulation of toxic salts in the plant - defense against insects even sometimes it may houses insects and larvae. - Secretory trichomes participate in chemical defense (resin, volatile oils, proteolytic enzymes , poisonous substance) plant Anatomy 254 lec.5 Rajaa Abueideh • Morphological groups of trichomes: 1) hairs - glandular (with unicellular or multicellular stalk and a secretory head with one to several cells) - Non-glandular : simple -unicellular or - multicellular – uniseriate -multiseriate branched - Stellate (star shaped) - dendroid (branched hair) Hairs of cotton seeds are unicellular and develop secondary walls at maturity (developed by elongation of protodermal cell) 2)Scales (peltate hairs) 3) Water vesicles which are enlarged epidermal cells ٤) Root hairs plant Anatomy 254 lec.5 Rajaa Abueideh magazine.com٤٢٠ plant Anatomy 254 pharamcytimes.wordpress.com lec.5 Rajaa Abueideh superstock.com Cotton hair seeds sciencedirect.com plant Anatomy 254 lec.5 Rajaa Abueideh Glandular trichomes Stinging hairs Mauseth plant Anatomy 254 lec.5 Rajaa Abueideh