Download Slide set 9 – Physiology – Transport and nutrition

Chapter 12 & 13
Transport, Soil and
Mineral Nutrition
Topics
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Methods of transport
Xylem transport
Phloem transport
Soils properties and nutrient absorption
Macro and micro essential nutrient elements
Too much or too little nutrients
Mobile or immobile nutrients within the plant
Deficiency symptoms
Special adaptations in N-poor soils
Plant mineral storage
Short distance - Diffusion, Osmosis,
and Active Transport
• Diffusion = random movement of particles from areas of high
concentration to low concentration
• Diffusion of water through a selectively permeable
membrane = osmosis
• selectively permeable membranes allow only certain
substances to pass through
• water molecules pass through all membranes, but pass
more rapidly if the membrane has protein channels called
aquaporins
• To move molecules against their gradient, energy (via ATP)
is necessary - this is active transport
Water Potential - ψ
• Water has free energy, capacity to do work,
chemical potential
• Chemical potential of water = water potential
(symbolized as ψ)
• When water adheres to a substance, the water
molecules form hydrogen bonds with the material and are
not as free to diffuse as are other water molecules
• So, water’s capacity to work has decreased when in
solutions
• Water moves from higher to lower ψ
Guard Cells
• For guard cells to open, K+ are actively transported
from surrounding cells into them
• Guard cell ψ becomes more negative and the adjacent cells
become less negative; results in a net movement of water
into the guard cell
• Guard cells become turgid and swollen, bending and
opening the pore due to uneven thickening of guard cell
wall
• Once open, pumping stops and water movement brings
guard cells and adjacent cells into water potential
equilibrium, and net water movement stops
Guard Cells
• The process is reversed for the
stomatal pore to close
• Guard cells of fully opened and
fully closed stomata are both in
equilibrium with surrounding
cells, even though they all have
different internal conditions
Control of Water Transport - Guard Cells
• Numerous mechanisms have evolved that control
stomatal opening and closing
• If the leaf has an adequate moisture content, then
light and carbon dioxide are the normal
controlling factors
• Blue light triggers stomatal opening
• Decrease in internal carbon dioxide concentration may
lead to stomatal opening
• Decreased air humidity - high wind - may close stomata
partially
• High T – leads to stomatal closure e.g. CAM plants
Control of Water Transport - Guard Cells
• These mechanisms in healthy plants are
completely overridden by a much more powerful
mechanism triggered by water stress
• Roots under water stress synthesize hormone, abscisic
acid (ABA) – transported to leaves, which immediately
causes guard cells to close the stomatal pore (ABA is
synthesized by apical buds and senescing tissues too)
• In water stress - pores are closed even under blue light
and low concentrations of CO2
Long-Distance Transport: Xylem
Xylem Transport - Tension-cohesion-adhesion model
Leaf
= –1.5 MPa
Atmosphere
= –80 MPa
Stem
= –0.7 MPa
Coleus Plant
Root
xylem
Root
= –0.4 MPa
Soil water
= –0.1 MPa
Transpiration – loss of water
vapor – mainly thru stomata
– for nutrient
uptake and cooling
Casparian strip – forces
selective absorption of
solutes (keep unwanted
solutes out) and help hold
water in xylem
Transpiration generates
tension on soil-plantatmosphere water path –
water flows along water
potential gradient
Phloem transport - Münch Pressure Flow hypothesis
XYLEM
Active loading by STM/CC/P
PHLOEM
complex, and polymer
trapping in STM at
source/leaf – greater sugar
conc. In STM – water
Companion cell
Sieve tube element
Direction of
water
movementof
Direction
sucrose movement
absorption from xylem –
increased turgor pressure –
mass flow toward sink active and passive unloading
in sink along pressure
gradient – pressure flow
hypothesis by Ernst Münch
Sieve tube
running through
length of plant
for phloem transport
Soils and Plants
Soil has both abiotic
(chemical + physical) and
biotic properties - minerals,
water, air, T, flora and fauna
Right soil is crucial for plants
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Supplies minerals
Holds water
Supplies air, T to roots
Acts as a matrix that
stabilizes plants
• Harbors nitrogen-fixing
bacteria, mycorrhiza, other
microbes
• Animals for plants
Texture – a crucial physical
property
Soil
Particles
Sand,
Coarse
Sand, Fine
Silt
Clay
(micelles)
Size range
(mm)
2.0 - 0.2
0.2 - 0.02
0.02 – 0.002
< 0.002
Soils and Mineral Availability: CE
• CO2 from root respiration reacts with soil water to produce
carbonic acid
• H+ from carbonic acid disrupt cations from soil micelle
(negatively charged mineral/clay matrix or organic matter)
• Roots cannot absorb cations directly from micelle – cation
exchange is crucial
Essential Elements
• Research in mineral
nutrition involves
growing the plant in
hydroponic solution
in which the chemical
composition is
carefully controlled e.g.
except one element –
see picture
• Elements that are
necessary for plant
growth = essential
elements/nutrients
Essential Elements
• Macro - needed in large
amounts
• Micro - needed in smaller
amounts
Criteria for essentiality
• Must be needed for normal
plant development through a
full life cycle
• No substitute can be effective
• Must be acting within the plant,
not outside it
Too Much
• Salty regions - some excrete
salt from salt glands on leaves
• Desert soils – sometimes too
much minerals – too alkaline
– too negative water potential
• Toxicity caused by elevated
levels of single minerals:
• Aluminum toxicity in acid soils
• High levels of heavy metals on
mine tailings, polluted soils
Too Little
Some soils - low concentrations of certain essential
elements - plants are unable to thrive on them
• Deficiency diseases are most commonly encountered in
crop plants or ornamentals
• Harvesting crops leads to soil depletion
• Fruits, seeds, tubers, and storage roots often have the
greatest concentration of minerals in a plant
Symptoms of Deficiency
One symptom common in many elements = chlorosis
• Leaves lack chlorophyll, tend to be yellowish, and are often
brittle and papery
Deficiencies of either nitrogen or phosphorus cause
accumulation of anthocyanin - coloration
• Leaves become dark green or purple
Lack of potassium or manganese causes necrosis
• Patches of tissue die
Mobile and Immobile Elements
• Chlorine, magnesium, nitrogen, phosphorus (picture
below), potassium, and sulfur - mobile elements
• After been incorporated into a tissue, they can still be
translocated to younger tissue
• If soil is exhausted - salvaged and moved to growing regions
Mobile and Immobile Elements
• Boron, calcium, and iron (picture below) are
immobile elements
• They remain in place after being incorporated into
plant tissue.
• In deficient soils - newer tissues show symptoms
Nitrogen from Animals
• Soils in bogs and swamps have very little nitrogen
available because of nitrifying and denitrifying
bacteria
• Many bog-adapted, carnivorous plants get
reduced nitrogen by catching animals
Hydnophtum
A mutualistic
ant plant
Storage of Minerals within Plants
All plant parts (except seeds) store minerals in
soluble form in central vacuoles
• Nitrogen is converted to compounds with multiple amino
groups
• Phosphates, sulfates, and other mineral nutrients - simply
sequestered in the same forms in which they are used
Seeds store minerals as polymerized forms, usually
in protein bodies