Unformatted Document Excerpt
Course Hero has millions of student submitted documents similar to the one
below including study guides, practice problems, reference materials, practice exams, textbook help and tutor support.
Course Hero has millions of student submitted documents similar to the one below including study guides, practice problems, reference materials, practice exams, textbook help and tutor support.
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