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Roots
Functions?
Essential For Plant Growth
• Root System & Soil Environment Have Great Effect
on Plant Life & Productivity
• Anchor Plant in Soil
• Store Food
• Reproduction
• 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
• Storage
– 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
Beet photo by Angelo Azeredo Lopes
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• Support & Anchoring
• Absorb Moisture
– Roots Provide Support For Upright Stem
Portions of Plants & Help Hold the
Plant in the Soil Against Wind & Rain
• Propagation (Creeping)
• Symbiotic Relationships With Microbes
– Lateral Branch Roots Arising
From Vertical Root
– Adventitious Buds Can Form at
Any Point Along the Roots
• Produce New Plants by
Sending Up Leafy Shoots
– Most of Taproot Can Extend
Below Cultivating Depth
– Produce Deeper, Horizontal
Branches When Upper Ones
Are Destroyed
– Can Grow Straight Downward
http://www.ca.uky.edu/agc/pubs/pat/pat1-6/10.jpg
How’s the Soil?
• Soil Moisture Level
• Soil Physical Condition
– Roots Can Grow Only Where
Root Pressure Is Greater Than
the Physical Pressures Exerted
Against the Roots
Angelo Azeredo Lopes photo
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• 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
• 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?
• Soil Aeration
– 20-25% of Soil Pore
Space Should Be Air
– Oxygen Needed For
Respiration
– Reduced Growth if Soil
Aeration < 10%
Nature Abhors It
• Except Hydrophytes
– Anaerobic
Microorganisms May
Produce Toxins
– CO2 in Soil Air Often
Higher Than in AboveGround Air
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Gravitropism
Root Systems
• 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
http://www.bioschool.co.uk/bioschool.co.uk/images/pages/geotropism_JPG.htm
Radicle
• First Root From a Seed Is the
Radicle
– Develops Into the Primary Root
Taproots
• 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
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
Secondary Roots
• Branch From 1° Roots or Arise From
Plant Stem Tissue
• May Be Roots From Underground
– Common in Grass Crops
• Fibrous
– Often Used for Flavorings & Medicine
– Hold Topsoil in Place & Prevent Soil Erosion
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Adventitious Roots
And More
• Tertiary Roots
– Arise From 2° Roots
• Quaternary Roots
– Arise From Tertiary Roots
• Quinary Roots
• Arise From Stem or Other NonRoot Meristems
• May Be 2° Roots
• Adventitious Stem Roots Usually
Originate at a Node
– Arise From Quaternary Roots
Photo By Jared Deckard, Natural Resource Specialist, Pomme de Terre Lake
• Aerial
Brace & Prop Roots
• Types of
Adventitious
Roots
• Penetrate Soil for
Anchorage
Tougher Than Nails
– May Penetrate
Soil
– May Attach to
Other Plants or
Objects
• Epiphytes
Taking Root!
Extent of Root Growth
• 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
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Oops
• Remove the Grow Bag!
• Bracing Gone Bad
• Rootbound
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
RootStructure
Structure
• Roots Grow From
Meristems Near the
Tip of Roots
kilby.sac.on.ca
http://klemow.wilkes.edu/BIO122-LabQuiz2.html
http://biology.uco.edu/bidlack/botany/botanypics/default.htm
• Root Cap Is at Tip
• Being Regenerated By the Root
Tip It Protects
http://www.lima.ohio-state.edu/academics/biology/archive/roots.html
• Above Root Cap Is an Apical (Tip)
Meristem Where Cells Divide Fairly
Rapidly
– 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
– Cells Deposited to the Sides, Leaving
Thin Gel-Like Coating on Soil
Particles
– High Energy Process
• 20-30% of Photosynthetic Energy!
http://www.lima.ohio-state.edu/academics/biology/images/onioncap.jpg
http://www.botany.hawaii.edu/faculty/webb/BOT410/Roots/ApicalMeristems.htm
http://www.lima.ohio-state.edu/academics/biology/images/onioncap.jpg
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• Above Meristem Is
Zone of Elongation
• 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
– 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
http://www.lima.ohio-state.edu/academics/biology/images/zeahair.jpg
• 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
Chapter 6 - Structure of Higher Plants
Roots
• Roots absorb/conducting water & minerals, and
anchor & support the plant.
– Some act as storage organs for photosynthesized food.
Dissolved mineral nutrients and water
required for growth are absorbed by
the root hairs, which are extensions
of the epidermal cells.
Figure 6-18 Section of epidermis of a young root
showing three stages (bottom to top)
in the development of root hairs.
http://www.backyardnature.net/roots.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
tab
Practical Horticulture 5 th edition
By Margaret J. McMahon, Anton M. Kofranek and Vincent E. Rubatsky
© 2011, 2007, 2002, 1988 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
Root Anatomy
Pith
http://ghs.gresham.k12.or.us/science/ps/sci/ibbio/plants/notes/introot.htm
http://www.tutorvista.com/content/biology/biology-iii/plant-histology/anatomy-monocot-root.php
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• Outermost Cells Called
Epidermis
Root Anatomy
– Single Layer of Cells on the
Root Surface
– Absorb Water & Nutrients
• Cross-Section
in Maturation
Zone Shows
Cells Have
Differentiated
• Next Is the Cortex
– Specialized
Functions
Pith
– Loosely Packed Cells
– Can Be Several Layers
Thick
– Conduct Water &
Nutrients to Vascular
Bundle
– Stores Food & Nutrients For
the Root
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
• Next Is
Endodermis
http://ghs.gresham.k12.or.us/science/ps/sci/ibbio/plants/notes/introot.htm
• Stele
– The Root Center Tissues
Including the Pericycle,
Phloem & Xylem
– Stele Diameter Is Larger
in Monocots Than in Dicots
– Single Layer of
Cells That
Separates the
Cortex From the
Vascular Bundle
– Regulates Types of
Absorbed
Nutrients Allowed
to Enter Vascular
Cylinder
• Pericycle
– Separates the Xylem & Phloem
– Layer of Meristematic Cells in
Dicots
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://ghs.gresham.k12.or.us/science/ps/sci/ibbio/plants/notes/introot.htm
• 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
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
• Pith
– 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
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Chapter 6 - Structure of Higher Plants
The Pathway of Water in Roots
The
Water Pathway
Roots
Figure 6-19 Left :Cross section of a young root showing the parts
of the primary plant body and their location. Right :
Developmental occurrences in the root tip, showing
the various components and their relative location.
tab
Practical Horticulture 5 th edition
By Margaret J. McMahon, Anton M. Kofranek and Vincent E. Rubatsky
• Symplast—Living Portion of Cells
• Apoplast—Spaces Between Cells
Video
© 2011, 2007, 2002, 1988 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/X/Xylem.html
Chapter 6 - Structure of Higher Plants
Roots
For the soil solution to enter the inner tissue (pericycle)
of the root, it must pass through the permeable
endodermal cell walls and the protoplast.
• Water & Nutrient
Transport
– 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
tab
Practical Horticulture 5 th edition
By Margaret J. McMahon, Anton M. Kofranek and Vincent E. Rubatsky
© 2011, 2007, 2002, 1988 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/X/Xylem.html
Unseen Partners
Rhizobium
•
•
•
•
•
•
Super roots
with Frankia
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
Frankia, nitrogen-fixing bacteria that
form associations with some plants
http://www.laspilitas.com/advanced/advroots.htm
http://filebox.vt.edu/users/chagedor/biol_4684/Microbes/rhizobium.html
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Azospirillum
• Nitrogen-Fixing Genus of
Bacteria in Many Grasses
Including Grain Crops
http://www.patentlens.net/daisy/bioforge_bioindicators/3201/version/default/part/ImageData/data/Rice%20Azospirillum.jpg
http://www.indiamart.com/prabhatfertilizerandchemicalworks/agricultural-fertilizers.html
•
•
•
•
•
•
Many secondary pioneer species are associated With Frankia. In California these include; Datisca glomerata, Ceanothus, Alnus, Cercocarpus, Myrica, Purshia,
Frankia fixes nitrogen From the air & produces
secondary chemicals That feed friendly associated free living
bacteria & fungi. The plant-mycorrhiza-frankia Tripartite
relationship Often becomes a multi-layered community of
associated free living & plant related organisms That protect &
support each Other. The relationships are complex With Only the most obvious presently recognized. The Different associated
Frankia
Cowania, Chamaebatia, & Shepardia species.
Nitrogen
Defense
Increase # Root Hairs
Mineral & Water Uptake
Transport of Hormones
Through Roots
•
organisms are responsible For root hormones, pathogen control, nematode control, root exploration, plant community resource sharing, mineral mining, water
retention & Many More. The plants become increasingly instable as these organisms are replaced With non-supportive or parasitic pathogens or weedy
organisms, Including weedy plants. These problems Can Be very difficult to diagnose as everything is interrelated, & human in tervention Can Often make the
problem worse.
Ceanothus get branded as short lived because the mychorriza-frankia & associates are Not properly allowed to develop & grow. Ceanothus Can live For a
hundred or More years in the wild, & commonly For twenty to fifty years in a garden, if the appropriate Ceanothi are planted & left alone. Watering &
fertilizing the plants More Than required fools the plant Into thinking That They do Not need friends & Can do all things the mselves. The plants, if They do Not
die That day From pathogens, grow fast & robust, Then die of pathogens.
http://www.laspilitas.com/advanced/pictures/ceanothus_frankia.jpg
• 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
http://www-mykopat.slu.se/
Newwebsite/mycorrhiza/kantarellfiler
/bilder/C.GIF
• Plants Communicate With Similar Chemical Warnings via
Roots & Through Air
http://ic.ucsc.edu/~wxcheng/envs161/Lecture8/
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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
• 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
Specialized Roots &
Vegetative Propagation
• Creeping Roots
ipcm.wisc.edu/uw_weeds/
– Dicots
– Roots Initiate Adventitious Shoots
– May Grow Deeply
– New Shoots Independent of Parent
– Killing Shoots Encourages Formation of
New Shoots
images/CanadaThistle03.jpg
http://www.btny.purdue.edu/Pubs/WS/CanadaThistle/roots.jpg
http://ianrpubs.unl.edu/weeds/graphics/spurge6a.jpg
• Tuberous Roots
– Abruptly Thickened Roots
– Appear to Be Tap Roots, But Often Are Types of 2° or
Adventitious Roots
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