Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Plant defense against herbivory wikipedia , lookup
Plant breeding wikipedia , lookup
Plant physiology wikipedia , lookup
Plant evolutionary developmental biology wikipedia , lookup
Plant ecology wikipedia , lookup
Plant secondary metabolism wikipedia , lookup
Glossary of plant morphology wikipedia , lookup
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