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9/19/2014 Roots Functions? Essential For Plant Growth • Root System & Soil Environment Have Great Effect on Plant Life & Productivity • Storage • Water & Nutrient Uptake – Most Uptake Occurs Near Root Tip, Through Root Hairs – 80% Absorption Occurs in Top 18 Inches of Soil – Plant Management Practices Will Affect Uptake Zones – Region of Greatest Root Volume Not Always Area of Greatest Water/Nutrient Uptake – Root Does Not ‘Grow Toward’ Water & Nutrients – Most of Carbohydrates Transported to Roots Are Used For Active Root Growth – Some Crops Will Store Carbohydrates in Their Roots For Later Growth/ Regrowth – Stored Carbohydrates Allow Plants to Produce New Shoot Growth • Support & Anchoring – Roots Provide Support For Upright Stem Portions of Plants & Help Hold the Plant in the Soil Against Wind & Rain • Anchor Plant in Soil • Store Food • Reproduction • Absorb Moisture • Symbiotic Relationships With Microbes • Propagation (Creeping) How’s the Soil? – Lateral Branch Roots Arising From Vertical Root – Adventitious Buds Can Form at Any Point Along the Roots • Soil Moisture Level • Soil Physical Condition • Produce New Plants by Sending Up Leafy Shoots – Roots Can Grow Only Where Root Pressure Is Greater Than the Physical Pressures Exerted Against the Roots – Most of Taproot Can Extend Below Cultivating Depth – Produce Deeper, Horizontal Branches When Upper Ones Are Destroyed – Can Grow Straight Downward • Soil Fertility & pH – Roots Grow Better, More Branching & Spread, in a Fertile Soil Compared to Less Fertile Soil – Roots Do Not Grow Toward Nutrients – Excess Nutrients in Soil – pH Beyond Optimum Ranges Result in Reduced Root Growth http://www.ca.uky.edu/agc/pubs/pat/pat1-6/10.jpg 1 9/19/2014 • Soil Aeration • Soil Temperatures in Root Zone – Optimum Usually Cooler Than For Above-Ground Plant Portions – Less Temp Fluctuation Than Above Ground – Temperatures Above Optimum? – Temperatures Below the Optimum? – Temp Affects Root Thickness & Branching – Effects of Moisture? – Effects of Soil Color? – Effects of Plant Canopy or Other Covering? – 20-25% of Soil Pore Space Should Be Air – Oxygen Needed For Respiration – Reduced Growth if Soil Aeration < 10% • Except Hydrophytes – Anaerobic Microorganisms May Produce Toxins – CO2 in Soil Air Often Higher Than in Above-Ground Air Gravitropism • Roots Grow Downward, With Gravity (Positive Gravitropism) • Due to Different Amounts of Plant Hormones Called Auxins in Different Parts of a Cell • Upper Side of Horizontal Root Grows More, Causing Root Tip to Turn Downward Root Systems • First Root From a Seed Is the Radicle – Develops Into the Primary Root • If Primary Root Continues to Grow & Develop, Plant Has a Taproot System – Can Grow Deeply Into Soil – Some Harvested For Food • Tap – Important Food Source – Also Source of Flavorings & Medicine – eg: Beet, Carrot, Parsnip, Radish, Turnip, Sweet Potato http://www.bioschool.co.uk/bioschool.co.uk/images/pages/geotropism_JPG.htm Fibrous Root System • Primary Root Does Not Develop Much • Fibrous Systems Are More Thoroughly Distributed & Absorb More Water & Nutrients Within the Root Zone Than Tap Root Systems • Allows Greater Contact Within Rooting Zone – Common in Grass Crops • Fibrous – Often Used for Flavorings & Medicine – Hold Topsoil in Place & Prevent Soil Erosion • Secondary Roots – Branch From 1° Roots or Arise From Plant Stem Tissue – May Be Roots From Underground • Tertiary Roots – Arise From 2° Roots • Quaternary Roots – Arise From Tertiary Roots • Quinary Roots – Arise From Quaternary Roots • Adventitious Roots – Arise From Stem or Other Non-Root Meristems – May Be 2° Roots – Adventitious Stem Roots Usually Originate at a Node 2 9/19/2014 • Brace & Prop Roots Taking Root! Extent of Root Growth – Types of Adventitious Roots – Penetrate Soil for Anchorage • Aerial • Root Dry Weight Is Usually 1/3 to ¼ of Total Plant Dry Weight (May Be More) • Root Surface Area Is at Least 20 to 30 Times Greater Than Leaf & Stem Surface Area • Knowing Extent of Root System Aids in Water & Fertilizer Placement – May Penetrate Soil – May Attach to Other Plants or Objects • Epiphytes Monocot vs. Dicot Monocot vs. Dicot Roots • Fibrous • Develops From Adventitious Roots • Scattered Vascular System Around Perimeter of Stele • Taproot • 1° Root Persists, Produces Branches & Continues as Main Root of Plant • Vascular System in a Cross in the Center of the Stele http://www.bio.miami.edu/dana/160/160S12_15.html • • • Fibrous Root System Root System Develops From Adventitious Roots Scattered Vascular System Around Perimeter of Stele • • • Taproot System 1° Root Persists, Produces Branches & Continues as Main Root of Plant Vascular System in a Cross in the Center of the Stele Image From Purves et al., Life: The Science of Biology, 4th Edition, By Sinauer Associates (www.sinauer.com) & WH Freeman (www.whfreeman.com), used With permission. 3 9/19/2014 Monocot vs. Dicot Stem http://www.bio.miami.edu/dana/160/160S12_15.html Dicot Monocot Structure • Roots Grow From Meristems Near the Tip of Roots • Root Cap Is at Tip • Being Regenerated By the Root Tip It Protects – Cells Deposited to the Sides, Leaving Thin Gel-Like Coating on Soil Particles – High Energy Process • 20-30% of Photosynthetic Energy! • Above Root Cap Is an Apical (Tip) Meristem Where Cells Divide Fairly Rapidly kilby.sac.on.ca http://klemow.wilkes.edu/BIO122-LabQuiz2.html http://biology.uco.edu/bidlack/botany/botanypics/default.htm • Above Meristem Is Zone of Elongation – 1 to 10mm Long – Newly-Formed Cells Take on Water & Elongate to Mature Size – Primary Function Is to Increase Root Length • Above Elongation Zone Is Differentiation Zone or Zone of Maturation – – – – Cells Actively Divide to Produce More Cells Dividing Cells Are Protected By the Root Cap Some Cells Are Used in the Root Cap Some Cells Become Root Tissues • Root Hairs Develop From Epidermal Cells • Once Epidermal Cells Cease Elongation, They Produce Tiny Extensions Into Soil Area • Up to 200 Root Hairs/mm2 of Root http://www.lima.ohio-state.edu/academics/biology/images/zeahair.jpg 4 9/19/2014 • Root Hairs Greatly Increase the Surface Area of a Root • 1-Month-Old Rye Plant = 14 Billion Root Hairs With Surface Area of ~4,300 ft2 • Reach Full Size in a Few Hours • Essential For Rapid Absorption of Water & Nutrients • In Typical Soil, Water Mostly Is Thin Film Surrounding Every Microscopic Soil Particle • Root Hairs Absorb This Water • Water Diffuses Molecule By Molecule Root Anatomy • Cross-Section in Maturation Zone Shows Cells Have Differentiated – Specialized Functions Pith http://www.backyardnature.net/roots.htm http://www.tutorvista.com/content/biology/biology-iii/plant-histology/anatomy-monocot-root.php http://ghs.gresham.k12.or.us/science/ps/sci/ibbio/plants/notes/introot.htm http://www.rsbs.anu.edu.au/profiles/Brian_Gunning/Web%20PCB/Ch%2002%20Introduction%20to%20Plant%20Cells/Topic%203%20AS&V%20Cells/02%2003%2001.htm • Outermost Cells Called Epidermis – Single Layer of Cells on the Root Surface – Absorb Water & Nutrients • Next Is the Cortex – Loosely Packed Cells – Can Be Several Layers Thick – Conduct Water & Nutrients to Vascular Bundle – Stores Food & Nutrients For the Root • Next Is Endodermis – Single Layer of Cells That Separates the Cortex From the Vascular Bundle – Regulates Types of Absorbed Nutrients Allowed to Enter Vascular Cylinder • Pith • Stele – The Root Center Tissues Including the Pericycle, Phloem & Xylem – Stele Diameter Is Larger in Monocots Than in Dicots • Pericycle – Separates the Xylem & Phloem – Layer of Meristematic Cells in Dicots • Vascular System – Very Center of Root – Made Up of Phloem & Xylem – Monocots • Xylem & Phloem Form Ring Around the Center of the Root – Dicots • Phloem Surrounds & Eventually Is Outside the Xylem • Xylem Will Be in the Very Center of the Root The Pathway of Water in Roots The Water Pathway – Found in the Center of a Monocot • Cambium – Cells Can Divide to Produce 2° Growth in Perennial Plants – Found Only in Dicots – Not Important in Annual Plants http://ghs.gresham.k12.or.us/science/ps/sci/ibbio/plants/notes/introot.htm • Symplast—Living Portion of Cells • Apoplast—Spaces Between Cells Video http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/X/Xylem.html 5 9/19/2014 • Water & Nutrient Transport Unseen Partners – Cortex to Endodermis • Casparian Strip – Through Endodermis to Pericycle – Then to Xylem – Moves Rapidly Upward in Plant to Stems & Leaves – Injury to Roots Can Reduce/Prevent This Flow • Rhizobium – Nitrogen-Fixing Species of Bacteria, Symbiotic Relationship With Legumes – N-Fixing Enzyme Nitrogenase • Converts Atmospheric N Into Ammonia, Gives N to Plant, Plant Gives Food to Bacteria • Azospirillum • Nitrogen-Fixing Genus of Bacteria in Many Grasses Including Grain Crops • Frankia – Nitrogen, Defense, Increase # Root Hairs, Mineral & Water Uptake – Transport of Hormones Through Roots • Mycorrhizae Plants Talk Through Mycorrhizae • Plants Use Underground Network of Fungi to Warn Each Other About Aphid Attacks – Have to Be Connected in Same Network – Send Out Chemical Signal That Repels Aphids & Attracts Predatory Wasps – Fungi Pay Plant Back by Transmitting Signal Efficiently • Plants Communicate With Similar Chemical Warnings via Roots & Through Air • Plants Warn Neighbors of Impending Danger by Wafting Chemical Signals Into the Air • 2 Genes in Rice Switch On in Response to Music & Clear Tones • Corn Roots Will Lean Toward Certain Vibrations • Chili Seedlings Don’t Like Fennel’s Sound • China Researchers Have Increase Yields With Sound Waves • Sounds Change Gene Expression Can Plants Hear? • ‘Hearing’ Affects Ability to Ward Off Pests • Researchers Played Noises of Caterpillars Munching on Foliage to 1 Group of Plants • Control Group Kept in Silence • Group Exposed to Sound Produced More Repellents When Real Caterpillars Set Loose Specialized Roots & Vegetative Propagation • Creeping Roots – Dicots – Roots Initiate Adventitious Shoots – May Grow Deeply – New Shoots Independent of Parent – Killing Shoots Encourages Formation of New Shoots • Tuberous Roots – Abruptly Thickened Roots – Appear to Be Tap Roots, But Often Are Types of 2° or Adventitious Roots 6