Plant cells and tissues.pptx

Plant cells Plant cells • Basically • a living cell (protoplast) plus a cell wall Protoplast bound by cell membrane (plasmalemma) Regulates passage of materials in and out of cell • Pressed tightly against cell wall because of very high internal pressure • • Turgor pressure – without the cell...

Plant cells Plant cells • Basically • a living cell (protoplast) plus a cell wall Protoplast bound by cell membrane (plasmalemma) Regulates passage of materials in and out of cell • Pressed tightly against cell wall because of very high internal pressure • • Turgor pressure – without the cell wall, plant cells would rupture Plant cells - organelles • The usual collection of organelles (with some variations) Nucleus – double walled • Endoplasmic reticulum • • • Rough ER – studded with ribosomes – site of manufacture of (especially) transmembrane proteins Smooth ER – where those transmembrane proteins are deposited. • Destined for processing in the Golgi apparatus Golgi apparatus (dictyosome) – Site of post-processing of proteins from smooth ER. • Moved from Golgi to destination organelle membrane or cell membrane • • Continuity CONCEPT of the internal membrane system = ENDOMEMBRANE Plant cells - organelles • Mitochondria – Cellular respiration Double membrane – internal highly folded into “cristae”. • ATP synthesis • Has its own DNA • Does most of its own housekeeping • Has prokaryotic origin (“endosymbiosis”) • • Microbodies – single membranes, enzymatic functions Peroxisomes – destroy oxides and peroxides (“reactive oxygen species” – ROS) created by UV light. • Glyoxysomes – in seeds – convert fats to carbohydrates during germination • Plant cells - organelles • Vacuole Largest organelle in mature plant cells (can be up to 90% of volume) • Fluid filled sac – membrane called TONOPLAST • Formed from small vesicles transported and processed by Golgi. • Responsible for maintaining turgor pressure of cell • Vacuole content – “cell sap” or “cellam sucus” • Water, atmospheric gas, ions, sugar, proteins • Organic acids – citrus fruits, etc. (citric acid) • Water soluble pigments (anthocyanins – another antioxidant chemical) • Insoluble salts – waste or defense (calcium oxalate crystals of Araceae – “raphides”) • Plant cells - cytoskeleton • Microtubules • Actin • Act – made of tubulin filaments together for motility, movement of materials through cells, cell contraction and shape, cytoplasmic streaming. Plastids • Also had a prokaryotic origin via endosymbiosis • Have their own DNA/do their own cellular housekeeping • Semiautonomous • Have double membranes similar to mitochondria • Develop from undifferentitated proplastids • Classified • All based on pigment and function can INTERCONVERT between plastid types. Plastids • Chloroplasts Contain chlorophylls and carotenoids • Responsible for photosynthesis • Inner membrane is thylakoid membrane • Thylakoids are pancake-like membrane formations embedded with photosynthetic pigment • Grana are stacks of thylakoids • Plastids • Chromoplasts Only contain carotenoids • Function to signal ripeness in fruits (chloroplasts in green tomatoes change to chromoplasts in ripe tomatoes), etc. • Plastids • Leucoplasts Colorless – no pigment • Store starch (amyloplasts), protein (aleuroplasts), or lipids (elaioplasts) • Example: starchy potato cells have large numbers of amyloplasts • Plant cells – the cell wall • Can • have a primary and a secondary cell wall Primary cell wall – living, herbaceous cell walls • • • • • • • Always the outermost wall Made of several molecules Mainly beta-cellulose strands Linked together by hemicellulose Embedded in a matrix of pectin, cutin, suberin, etc. Cells glued together by a middle lamella of pectin Have plasmodesmata • Living, membrane lined passages from one cell to another • Chemical communication between cells Secondary cell wall • Laid down INSIDE primary cell wall • Laid down after cell growth is completed • For structural support and conduction of materials • Can • have up to three laminated (like plywood) layers S1, S2, S3 • Embedded • Cell in matrix of LIGNIN (wood) for rigid structure dies after secondary cell wall is completed A number of plant cells only reach functional maturity after they die (apoptosis) • Plasmodesmata then become known as PITS. • Plant tissues •3 • tissue systems Ground tissue Parenchyma • Collenchyma • Sclerenchyma • • Vascular tissue Xylem • Phloem • • Dermal tissue • Epidermis Ground tissue - parenchyma • Makes • Cell up the bulk of the “filler tissue” in soft parts of plants is thin-walled, isodiametric, living at maturity • Many types of specialized cells Photosynthesis • Starch storage • Secretion (resin ducts, laticifers, etc.) • Wound repair (remain meristematic) • Ground tissue - collenchyma • Elongated and irregularly thickened Provide flexible structural support. • Usually alive at maturity • Ground tissue - sclerenchyma • Lignified • Dead • Two support tissue at maturity types Fibers – jute, hemp, flax, etc. • Sclereids – small bundles of sclerenchyma • Stone cells of pears • Shells of many seeds • Vascular tissue - xylem • Moves water up (only) from the roots to the leaves • Water is moved via root pressure, capillarity, and transpirational pull • Made up of two elements • Tracheids • • • • Serve as structural support and transport More primitive type of xylem Usually alive at maturity Vessel elements • • • • Grow end-to-end to form a continuous tube Elements “Pipes” through which a plant moves water and minerals Dead at maturity Tracheids and vessel elements Vascular tissue - phloem • Transports sugars (up and down) from the leaves or storage tissues to all parts of the plant. • Sap is moved via active cell processes (energy expenditure) • Made • Sieve tube cells • • up of two elements The “pipes” through which the sugars are transported Companion cells • Command centers which regulate osmosis, movement of sugars into and out of phloem Sieve tube and companion cells Dermal tissue • Continous, unbroken layer of tissue Serves as a protective layer against injury, herbivory, water loss • May be specialized as guard cells, root hairs, trichomes •