Plant Histology Summary PDF

Plant Histology By Sara Meame  Introduction Plants Animals Food By photosynthesis Feed on other organisms Growth Unlimited growth Limited growth...

Plant Histology By Sara Meame  Introduction Plants Animals Food By photosynthesis Feed on other organisms Growth Unlimited growth Limited growth Cell wall Present Absent Centrioles Absent Present Plastids (Chloroplast, Present Absent chromoplast) Central vacuole Present Absent Shoot Stem + leaves + fruits + Reproductive structures Roots  Cell wall v Is strong & rigid. v Provides mechanical support & protection + allow the transportation of materials through plasmodesmata. v Not selectively permeable v Synthesized by protoplasm but not a part of it. v Middle lamella = between cells, made up of pectin (viscous => cement like) Secondary cell Primary cell wall wall (Outer) (Inner)  Primary Cell Wall Secondary Cell Wall 1. Laid down against the middle lamella 1. Much thicker than the primary cell wall 2. Plastic & capable of extension => allow the growth of plant in length & in width 2. –Location: Hard parts of the plant. 3. –Can increase only in thickness 3. Has NO differentiated cells 4. Contains lignin => provides rigidity for the Composed of: plant. –Cellulose: in the form of irregular fibers { cellulosic molecules + hydrogen bonds => 5. Made up of 3 layers (lamellae), each one microfibrils => macrofibrils => fibers) consist of cellulosic fibers arranged in Cellulose= 3,000 linked glucose => unbranched parallel & making an angle 60* with the polysaccharide. other lamella. –Hemicellulose: mixture of NEUTRL 6. Mature cells with 2nd cell wall => dead cells polysaccharides = pentoses (xylose & (role: mechanical support) arabinose) + hexoses (galactose, mannose, Plasmodesmata: glucose) Are small wholes in the wall with Pectin (acidic polysaccharide) + glycoproteins protoplasmic connections Found in areas called Pits = areas where cell wall is thin + NO 2nd cell wall  Plant Tissues Meristematic Permanent Primary Secondary Ground Protective Vascular Xylem Parenchyma Collenchyma Sclerenchyma Ploem Sclerenchyma Sclerides Aerenchyma Chlorenchyma fibers  Meristem v Undifferentiated embryonic tissue => NO specialization v No space between its cells Primary meristem (Apical) Secondary Meristem-Cambium=Lateral –found in growing apics of plant organ –found in the stem & roots (between the –generative layer conductive tissues) –Provide the growth in Length = Primary –Allow the increase of thickness= Secondary growth Growth. –Cells: Cells: Isodiametric Cylindrical No plastids NO plastids Many mitochondria Nucleus is smaller than the primary one Large nucleus Large vacuole Few (or no) vacuoles Packed with THIN cellulosic wall Vascular Cambium Packed with THIN cellulosic wall Cork cambium Produces 2nd tissues that Found between the function in support & cork & phelloderm conduction  Apical Meristems Provide Primary growth (growth in length) Found on the tips of roots & stem Produces new leaves & flowers Lateral Meristems Provide Secondary Growth (in width) Found at cambium Produce bark on trees  Protective Tissue v It cover the plant body. v Role: is to protect the other tissues from external factors: rain, drought & resistance to water impermeability. Epidermis Periderm 1) Epidermis: v It covers the outer tissue of plants, it’s a primary tissuefrom apical mer. v Role: prevent mechanical injury & water loss. Epidermal Cells: –Irregular shape Stomata (pores): –NO intercellular space => Good barrier –Location: in leaves & young stems –Living cells with thin cytoplasm + NO –Function: Gas exchange chloroplast (except in aquatic one) + cell –Surrounded by guard cells (for wall covered by Cuticle (cutin: consist of adaptation) fats + wax) => prevent water loss (thick: –Sub stomatal Chamber = air chamber = in drought areas & thin: humid areas) + space below each stoma protect against mechanical injury NO CUTICLE in piliferous layer (Root tip) Hydathodes (water pores): Epidermal appendages = Epidermal –Function: get rid of excess water Hair: (guttation) –outgrowth of epidermal cells –Location: at leaf border –Function: protect the plant from biotic & –NOT associated with sub stomatal abiotic factors. chamber or guard cells 2) Periderm: v Stem & Roots grow in thickness => replacement of epidermis by periderm that is composed of: 1. Cork cambium 2. Some parenchymal cells v Cork is composed of: 1. Dead flat cells with suberified (suberin) 1st cell wall. 2. NO intercellular space 3. Gas lenticels = openings to allow the exchange of gases with the living cells. 4. Replacement of the old cork by a new cork is done by cork cambium  Ground Tissues 1) Parenchym: v Soft tissue v Produced by Primary or Secondary meristem. v Cells: isodiametric + thin primary cellulosic cell wall + intercellular space. A– Chlorenchyma = Chlorophyll Parenchyma: Location: Aerial green parts Function: chloroplasts => photosynthesis. Presence of intercellular space between its cells. In leaves it is called Mesophylls, covered by epidermis & crossed by veins.  Monocotyledon => homogenous mesophyll Dicotyledons => heterogenous mesophyll Palisade parenchyma Spongy Parenchyma Location: Upper or Ventral Location: Lower or dorsal Consist of one or many layers of Function: help in photosynthesis by elongated chloroplastic cells communicating with stomata –NO intercellular space –Formed of round cells B) Reserve Parenchyma: Location: roots, stem, seeds Function: storage of nutrients => NO chloroplast. Note: Succulent plants store water (aquifer parenchyma) Starch Sucrose Oils Protein Cellulose Potato Beet Seeds Wheat grain Date seeds  C) Aerenchyma: Abundant intercellular spaces full of air. Function: air circulation between roots & shoots 2) Collenchyma: v Is a Primary Supportive tissue. vLocation: Aerial organs. vFunction: flexibility, support, streching, & strengthening of growing & mature tissues. vComposed of: 1. Elongated living cells + NO AIR SPACES 2. Large surrounded by thin cytoplasm, NO 2nd Wall 3. Differ than Parenchyma by: thickness of 1st cell wall (thicker in collenchyma) Annular Collenchyma Angular Collenchyma Lamellar Collenchyma Collenchyma with Thickenings are at the Thickenings are on the uniformly thickened cell intercellular contact tangential wall wall points 3) Sclerenchyma: v Is DEAD supportive tissue (Primary or Secondary). v Location: in old organs of plant’s body v Secondary cell wall of its cells are heavily lignified & thick => NO AIR SPACE => harder than collenchyma. v It is composed of: 1. Fibers: elongated fusiform cells. –Location: seeds, roots, fruits, leaves. –Function: textile industry 2. Sclerids = stone cells: are short with very thick lignified cell wall -Location: hard seeds & fleshy fruits (apple, pears) Conducting or Vascular Tissues v Can be primary or secondary complex tissues v Location: in vascular plants vFunction: allow the circulation of sap in the parts of plant vComposed of 2 tissues: Xylem Ploem 1) Xylem: v Function: ensures the circulation of crude sap (very diluted aqueous solution) = mineral salts + water. vCan be primary or secondary tissue (wood) vComposed of: 1. Conducting elements (tracheids) 2. Vessels 3. Parenchymal cells 4. Fibers 1) Tracheids: Primitive conducting elements found in all vascular plants Are elongated cells tapered at there end + heavily lignified 2nd cell wall => support + sap conduction. Sap circulation occurs through pits (numerous at tapered part of tracheids) Mature primary xylem Secondary Xylem Tracheids stretch during the –in gymnosperms & dicots development of plant After lengthwise Þ NON-Functional growth is ceased Tracheids are not stretched & Þ 2nd cell wall will be in the they have large lumen form of rings.. 2) Vessels: Specialized conducting elements Made up of dead cells called vessel elements, they form a large cavities bounded by lignified cell wall + large lumen. Vessels are formed by the breaking down of transverse wall forming a perforation plate (‫)ﺛﻘب‬ Highly perforated transverse wall => compound perforation Dissolved transverse walls => simple perforation (‫)ﺛﻘب‬ Fibers provide support to tracheids 3) Parenchymal cells: Living cells provides the lateral conduction of sap. 2) Ploem: v Conducts sap (organic nutrients produced by photosynthesis) throughout the plant parts. vCan be Primary or Secondary Complex tissue. v Composed of: 1. Sieve Cells 2. Sieve tubes 3. Companion 4. Parenchymal cells 5. Fibers 1) Sieve cells: Living cells & Elongated with thin cellulosic wall perforated by pores + central vacuole 2) Sieve tubes: Found in angiosperms. Made up of superposed tubular cells surrounded by oblique cellulosic cell wall called Sieve plate ‫( ﻏرﺑﺎل‬allow the transport of small ,molecules ex: proteins) 3) Companion cells: Associated with sieve tubes Communicate with them through numerous plasmodesmata  Its nucleus controls its cytoplasm & the cytoplasm of the adjacent Sieve cell (bcz sieve’s nucleus will disintegrate at maturity) Function: when sieve cells die, companion cell divides longitudinally to give 2 cells => 1 will replace the sieve cell & the other is the companion cell. 4) Parenchymal Cells: –are living cells –Role: lateral conduction + storage of sap 5) Fibers: less abundant than that of Xylem  Secretory Tissues v They are localized in specific parts of the plant vConsists of Parenchymal cells or epidermal cells vInvolved in the secondary metabolic products (oils, tanins, resin, latex..) vThey can accumulate there products in there cells or secrete them in cavities. 1. Secretion cells isolated with the parenchyma cells: Secretion cells, accumulate products in their vacuoles 2. Secretory epidermis and glandular hairs: Epidermal cells develope and stores essential oils in cytoplasm Multicellular, secretory (glandular hairs) accumulate essential oils in their terminal cells (lavendar) 3. Glands and canals Globular cavities, surrounded by cells which excrete products Extend all the length of plants => tube-like secretion canals or ducts 4. Laticiferous tissue: Contain secretory tubes (laticifer) elaborating the latex Latex: (milky white or colored) which is viscous liquid (water, sugar, mineral salts and organic acids). Laticifers are limited by cellulosic primary wall. Articulated Non-articulated single cell laticifer, arranged single elongated large, in rows, remain many nucleus(coenocyte) independent The end..