Chapter_04_Effects_of-Pathogens_on_Plant_Physiology
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Chapter_04_Effects_of-Pathogens_on_Plant_Physiology

Course Number: AGH 483, Fall 2008

College/University: Missouri State

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AGH 483 Diseases of Economic Plants Fall 2007 Lecture 4: Effects of Pathogens on Plant Physiology Physiology o Photosynthesis o Translocation o Respiration o Toxins May Inhibit P/S Enzymes o Decrease in Chlorophyll o Membrane Permeability o Transcription and Translation Photosynthesis Content o Chlorosis o Closed Stomata Xylem o Water and Minerals Absorbed by Roots o Translocated through the Xylem Vessels...

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483 AGH Diseases of Economic Plants Fall 2007 Lecture 4: Effects of Pathogens on Plant Physiology Physiology o Photosynthesis o Translocation o Respiration o Toxins May Inhibit P/S Enzymes o Decrease in Chlorophyll o Membrane Permeability o Transcription and Translation Photosynthesis Content o Chlorosis o Closed Stomata Xylem o Water and Minerals Absorbed by Roots o Translocated through the Xylem Vessels of the Stem o Into Vascular Bundles of Petioles and Leaf Veins o Enter the Leaf Cells o Most of the Water Evaporates and Diffuses into the Atmosphere via the Stomata o Results in Water Tension in the Xylem o Pulls the Water Column Upward o Stimulates additional Uptake Pathogens Interfere with Normal Translocation Process o Flow of Nutrients or Water Blocked Disease in Affected Cells/Tissues Inability to Carry Out Functions Shortage of their Products Disease in Entire Plant How Can Pathogens Impair Translocation of Water and Inorganic Nutrients? o Root Damage *DampingOff Fungi *RootRot Fungi, Bacteria *Most Nematodes *Some Viruses o Mechanisms of Damage *Cause Direct Injury to Roots *Inhibit Root Hair Production 1 *Alter Permeability of Root Cells o Xylem Gets Destroyed *Rot or Canker Pathogens *Gall Formation o Xylem Gets Clogged *Growth of Vascular Wilt Pathogens *Pathogen Secretions *Secretions of Tylose by Plant in Response to the Pathogen Excessive Transpiration Occurs when Pathogens Damage Leaves, Stomata o Leaf Cuticle Protects against Excessive Water Loss *Rusts, Mildews and Apple Scab Destroy Considerable Portion of Cuticle and Epidermis *Loss of Turgor and Wilting of Leaves *Suction Forces may Lead to Collapse or Dysfunction of Underlying Vessels Phloem o Carbohydrates Produced in Leaf Cells Move through Plasmodesmata into Adjoining Phloem Elements o Move down Phloem Sieve Tubes o Move into Nonphotosynthetic Cells or into Storage Organs o Nutrients Are Removed from `Circulation' How Can Pathogens Impair Translocation in the Phloem? o Movement of Substances from Leaf Cells to the Phloem o Translocation through Phloem Elements o Movement from Phloem into Cells that will Use the Nutrients o Obligate Fungal Parasites (eg: Rust and Mildew) *Respiration Increases *P/S Decreases *However, Photosynthetic Products Accumulate in Invaded Areas *Apparently Nutrients from Uninfected Areas Are Translocated toward the Infected Areas o Viruses *Viruses that Cause LeafCurling and some Yellows Diseases Cause Death of Phloem *Some Viruses Inhibit Enzymes that Break Down Starch into Smaller, Translocatable Molecules Plant Respiration o Cells Break Down Carbohydrates to CO2 and H2O in Series of Steps C6H12O6 + 6O2 6CO2 + 6 H2O o Energy Released when the Carbohydrate Bonds Are Broken Is Used for `Work' 2 Cellular *Accumulation and Mobilization of Compounds *Synthesis of Proteins *Activation of Enzymes *Cell Growth and Division *Defense Reactions o One of first Functions Affected when Plants Are Infected by Pathogens Disease = Respiration o Shortly after Infection--by the Time the Symptoms Are Visible *Rate Continues to Rise during Multiplication and Sporulation of the Pathogen *Declines to Normal or belowNormal Levels *Rate Increases more Rapidly in Resistant Varieties o Increased Respiration Depletes Plant's Reserves o Changes Metabolism *Increased Activity of Enzymes *Increased Synthesis, Accumulation and Oxidation of Phenolics Cell Membranes o Double Layer of Lipid Molecules o Protein Molecules Embedded *Parts usually Protrude on One or both Sides of Lipid Bilayer o Membranes Are Selective Barriers *Allow Entry of Substances the Cell Needs *Inhibit Passage out of the Cell o Cell Wall Keeps Large Molecules away from Membrane o Small WaterSoluble Molecules such as Ions, Sugars and Amino Acids Flow through or Are Pumped through Membrane Channels (Proteins) o Disruption of the Cell Membrane Alters Permeability *Uncontrollable Loss of Useful Substances and Entry of Harmful Substances Membrane Permeability Is often the First Detectable Response of Cells to Infection *Leakage of Electrolytes *Unknown if Membrane Leakage Is 1 or 2 Effect *If Direct Attack, Pathogens probably Use One of the following Strategies *Stimulate MembraneBound Enzymes that Pump H+ in and K+ out *Interfere with Maintenance and Repair of Membrane's Fluid Film *Degrade the Lipid or Protein Components of Membrane Transcription and Translation 3 *Transcription *Copying Coding on DNA onto Messenger RNA *Translation *Use of Messenger RNA as a Template to Produce Proteins *Disturbances of any of the Processes may Affect Expression of Genes and Cause Drastic, Unfavorable Changes in Structure and Function of Affected Cells Effect on Transcription *Some Pathogens Change Composition, Structure or Function of Chromatin Associated with Cell DNA *Virus Uses Host Cell's Nucleotides and Machinery to Make Its own RNA *Sometimes See Activity of Enzymes that Break Down RNA *Pathogen may Be Forcing Plant to Produce New Kinds of Enzymes not Produced in Healthy Plants *Higher Levels of RNA in Infected Plants, especially Resistant Ones *Probably Due to Increased Synthesis of Substances Involved in Defense Mechanisms Effect on Translation *Higher Energy Needs *Increased Activity in Enzymes Associated with Respiration *Increased Production of Phenolics or Oxidation of Phenolic Compounds *Used in Defense Reactions *Resistant Plants Have Protein Synthesis in First few Minutes of Infection *Levels Remain High up to 2 to 20 Hours after Inoculation 4
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