Secretory Structure

Slides Lab.No.4 Secretory structure Prepared: 1-Tilia stem c.s 2- Pinus stem c.s (demonstration) 3- Ginkgo leaf c.s or stem c.s. (demonstration) Fresh specimens 1) Atriplex 2) Pelargonium branch 3) Urtica 4) Citrus 5) Euphorbia 6) Allium bulb with scales (boiled and non-boiled) 7) Rosemary leaves 1 Lab.No.4 Secretory structure Secretion means synthesis, segregation and release of materials that are functionally specialized or for storage or excretion. -secretion includes both removal of materials from the cell and accumulation of secreted materials in some compartments of the cell -External secretory structures: Those that secrete secretory product to ouside of the plant body 1- Nectary : -multicellular glandular structure -secreting liquid containing organic substance including sugars (nectar) - could be floral (from flower: to attract pollinators) or extrafloral (from vegetative plant parts) 2- Hydathodes:- structural modification of vascular and ground tissues usually in the leaf to release water directly to outside of the plant by root pressure through a pore in the epidermis. 3- Salt and chalk glands: Halophytic (salt-loving plants) frequently have glandular structures on stems and leaves that allow them to eliminate excess salts. Atriplex and Tamarix are famous examples, *** 1) Note the treads of salt on the surface of the new stems and leaves. Examine it under a dissecting microscope. The salt gland in Tamarix produce magnesium sulfate and calcium carbonate 4- Glandular trichomes with unicellular or multicellular stalk and a secretory head with one to several cells A) Glandular hair with unicellular head ***2) Prepare a thin c.s of the stem of Pelargonium, mount it and observe under low power. Trichomes of Pelargonium are present in a variety of levels of complexity. Frequently, the multicellular hairs have the ultimate cell modified into a swollen, glandular structure (unicellular) *** also examine glandular trichomes with unicellular gland in leaves of Rosemary using the dissecting microscope and try to make a thin cross section in the leaf, then examine using the compound microscope B) Glandular hair with multicellular head ***3) Prepare a thin c.s or paradermal section of the leaf of Lycopersicon, (tomato) mount it and observe under low power 2 C) Stinging hair with multicellular base ***4) Prepare a thin paradermal section of the stem of Urtica, mount it and observe under low power. Also examine the stem or the leaf using the dissecting microscope. -Internal Secretory Structures A) Secretory cells 1-Oil cells 2- Mucilagenous cells: cells containing mucilage (carbohydrates like gums and mucilage that swell in water) ***5) Examine a prepared slide for Tilia stem c.s Notice -mucilage containing cells in pith and cortex. 3- Resineferous cells: cells containing resin 4- Tannineferous cells: cells containing tannin Usually located in pith or phloem tissue *** 6) Examine prepared slide for Pinus stem c.s (conifers) Notice the following: - resin ducts in xylem tissue - tanniniferous cells in pith and phloem B) Secretory cavities or canals 1- Resin duct or canal (formed schizogenously) ***notice prepared slide with c.s. in Pinus stem and notice those resin canals or ducts. 2- Oil canals and Mucilage canals (formed lysigenously) ***7) Examine using the compound microscope a Citrus leaf and notice those oil ducts (take part of the leaf and put in a slide (wet mount preparation) You may use the dissecting microscope for this purpose instead of the compound microscope. ***9) Examine a prepared slide for Ginkgo leaf c.s or stem c.s and notice the mucilage ducts. C) Laticifers Cells or series of connected cells that contain latex (fluid of complex composition) ***9) Examine a drop of latex collected form Euphorbia or Nerium or Ficus plant by making wet mount preparation using the compound microscope. Draw what you will observe -Laticifers that secret latex could be: 3 A) Articulated laticifers [compound laticifers] Derived from series of interconnected cells, their intervening wall dissolved. Could be branched and unbranched. ***10) Prepare a slide for Allium bulb scales (white leaves) notice the laticifers which will appear as a whitish network [without boiling]. A small part of this net placed on a slide and examined under high power shows the thickened walls. Coagulating the latex by boiling the scales. Observe boiled onion scales to see the chains of latex cells occurring between the second and the third layers of parenchyma on the abaxial side of scales (ventral side that faces the organ), laticifers appear as longitudinal rows of opaque cells. They are filled with a cloudy granular fluid. B) Nonarticulated Laticifers. Simple laticefers , could be branched or non branched ***11) Prepare slide from partly macerated stem from Euphorbia, notice the simple unbranched laticifers. 4