Download Roots - Missouri State University

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
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• 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
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• 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.
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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
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• 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
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• 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
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