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Chapter 12 & 13Transport, Soil and

Mineral Nutrition

Topics

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

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Water Potential - Water has free energy, capacity to do work,

chemical potential Chemical potential of water = water potential

(symbolized as ) 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, waters capacity to work has decreased when in solutions

Water moves from higher to lower

Guard Cells For guard cells to open, K+ are actively transported

from surrounding cells into them Guard cell 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

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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

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Transpiration loss of water vapor mainly thru stomata for nutrient uptake and cooling

Casparian strip forcesselective absorption of solutes (keep unwanted solutes out) and help hold water in xylem

Transpiration generates tension on soil-plant-atmosphere water path water flows along water potential gradient

XylemTransport Tensioncohesionadhesionmodel

Leaf= 1.5 MPa

Atmosphere= 80 MPa

Stem= 0.7 MPa

Rootxylem Root= 0.4 MPa

Soil water= 0.1 MPa

Coleus Plant

Active loading by STM/CC/P complex, and polymer trapping in STM at source/leaf greater sugar conc. In STM waterabsorption from xylem increased turgor pressure mass flow toward sink -active and passive unloading in sink along pressure gradient pressure flow hypothesis by Ernst Mnch for phloem transport

Sieve tuberunning throughlength of plant

XYLEM PHLOEM

Companion cellSieve tube element

Direction ofwater movementDirection ofsucrose movement

Phloem transport - Mnch Pressure Flow hypothesis

Soil has both abiotic (chemical + physical) and biotic properties - minerals, water, air, T, flora and faunaRight soil is crucial for plants

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

Soils and Plants

SoilParticles

Sizerange(mm)

Sand,Coarse

2.0 0.2

Sand,Fine 0.2 0.02

Silt 0.02 0.002

Clay(micelles)

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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

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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 LittleSome 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 DeficiencyOne 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

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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

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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

HydnophtumA mutualistic ant plant

Storage of Minerals within PlantsAll 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