2006- 2007 resource acquisition & transport in plants chapter 36
TRANSCRIPT
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2006-2007
Resource Acquisition & Transport in
PlantsChapter 36
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Adaptations for Acquiring Resources Land plants inhabit 2 worlds:• Above ground – shoots acquire
sunlight and CO2
• Below ground – roots acquire water and minerals
Early land plants absorbed water, minerals and CO2 directly from or near a water source
As land plants increased in number, there was competition for resources
Plants developed specialized tissues to allow them to be successful in areas further from water
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Shoot Architecture & Light Capture
Leaf size and structure accounts for much of the outward diversity in plant form
Largest leaves are found in tropical species, smallest in dry or cold environments
Photosynthesis is affected by leaf arrangement, orientation and height
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Root Architecture and Acquisition of H2O and Minerals
The evolution of root branching enabled land plants to more effectively acquire water and nutrients from different types of soil while providing strong anchorage
The evolution of mutualistic associations between roots and fungi called mycorrhizae allowed plant to live in poorly developed soils
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Pathways of Transport in Plants Apoplast - everything external to the plasma
membranes of living cells
• Cell walls
• Extracellular spaces
• Interior of vessel elements and tracheids
Symplast – entire mass of cytosol of the living cells in a plant
• Includes plasmodesmata and cytoplasmic channels that interconnect them
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Transport in Plants
H2O & minerals• transport in xylem
• transpirationo evaporation, adhesion & cohesion
o negative pressure
Sugars• transport in phloem
• bulk flowo Calvin cycle in leaves loads sucrose into phloem
o positive pressure
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Gas exchange• photosynthesis
o CO2 in; O2 out
o stomates
• respiration
o O2 in; CO2 out
o roots exchange gases within air spaces in soil
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Ascent of Xylem Fluid
Transpiration pull generated by leaf
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Water & mineral absorption
Water absorption from soil
o osmosis
o aquaporins Mineral absorption
• active transport
• proton pumps
o active transport of H+
H2O
root hair
aquaporin
proton pumps
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Mineral Absorption
Proton pumps
• active transport of H+ ions out of cell
o chemiosmosis
o H+ gradient
• creates membranepotential
o difference in charge
o drives cation uptake
• creates gradient
o cotransport of othersolutes against theirgradient
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Water Flow Through Roots
Porous cell wall
• water can flow through cell wall route & not enter cells
• plant needs to force water into cells
Casparian strip
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Controlling the Route of Water in Root
Endodermis
• cell layer surrounding vascular cylinder of root
• lined with impermeable Casparian strip
• forces fluid through selective cell membrane ofiltered & forced into xylem cells
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Root Anatomy
dicot monocot
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Mycorrhizae Increase Absorption
Symbiotic relationship between fungi & plant• symbiotic fungi greatly increases surface area for
absorption of water & minerals
• increases volume of soil reached by plant
• increases transport to host plant
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Mycorrhizae
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Transport of Sugars in Phloem
Loading of sucrose into phloem• flow through cells via plasmodesmata
• proton pumpso cotransport of sucrose into cells down
proton gradient
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can flow 1m/hr
Pressure Flow in Phloem
Mass flow hypothesis• “source to sink” flow
o direction of transport in phloem is dependent on plant’s needs
phloem loading• active transport of sucrose
into phloem
• increased sucrose concentration decreases H2O potential
water flows in from xylem cells• increase in pressure due to
increase in H2O causes flow
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Chloroplasts
Epidermal cell
NucleusGuard cell
Thickened innercell wall (rigid)
Stoma open Stoma closed
H2O
water moves into guard cells
H2O H2O H2O
H2O H2O
H2O
H2O
H2O H2O H2O H2O
Control of Stomates
Uptake of K+ ions by guard cells• proton pumps
• water enters by osmosis
• guard cells become turgid
Loss of K+ ions by guard cells• water leaves
by osmosis
• guard cells become flaccid
K+
K+
K+
K+
K+ K+
K+ K+
K+ K+K+K+
water moves out of guard cells
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Control of Transpiration Balancing stomate function
• always a compromise between photosynthesis & transpiration
o leaf may transpire more than its weight in water in a day…this loss must be balanced with plant’s need for CO2 for photosynthesis