Mineral Nutrition

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Mineral Nutrition

• Chapter 7

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Why study the physiology of mineral nutrients in
plant tissue?
By understanding the principles that govern
nutrient availability and their role in
respective aspects of plant metabolism, we
increase our chances of growing healthy plants
and performing better research. Example If we
are testing the effect of a given treatment like
row spacing, we certainly want to avoid a
nutrient deficiency.
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• Minerals and water move primarily through xylem
• Concentration of minerals in xylem sap is
  different than in the soil solution
• So what?

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Conditions for Mineral Uptake

• Mineral must be dissolved in soil solution
• Root tissue must have O2 so ATP can be produced

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Essential Elements
An element that is required for a plant to
complete its life cycle
or
An element that is part of some essential plant
constituent or metabolite
From Hopkins, 1999
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Macronutrients

• C
• H non-fertilizer elements
• O
• N
• P
• K
• Ca
• Mg
• S

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Micronutrients - Trace Elements

• Fe
• Cu
• Mn
• Zn
• Mo
• Cl
• B
• Ni

Beneficial micronutrients Na, Si, Co, Se
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See Hopkins Café. Mighty Clean. Mob comes in.
C H O P K N S Ca Fe Mg Cl Mo B Cu Zn Mn Ni
Why are Si and Na not required? They are very
prevalent.
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Functions of Elements

• C,H,O - for photosynthesis to produce
  Carbohydrates
• C,H,O,N,S - Proteins
• C,H,O,N,P - Phospholipids (membranes)
• Ca - middle lamella
• Mg - chlorophyll, ATP reactions
• P - membranes, ATP, DNA
• K - turgidity of cells, enzyme activator
• Cl - turgidity of cells and enzyme activity

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What is the critical concentration?
A tissue concentration below which growth is
limited by 10.
A toxic concentration can be defined as the
concentration above which growth is limited.
Nutrient concentrations in between critical and
toxic are termed adequate.
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From Hopkins, 1999
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Phosphorous - P
1. Often absorbed as H2PO4- , HPO42- . 2.
Availability is low at high pH, Ca and Mg
phosphates form. 3. Deficiency symptoms include
intense green coloration of leaves.
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Phosphorous - P
4. In a sense, excess P is the opposite of excess
N because excess P reduces shootroot ratio. 5.
As already covered, P is required for membranes,
sugar phosphates, nucleotides.
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Potassium - K
1. Important in enzyme activation 2. Important
for osmoregulation (e.g., stomatal function). 3.
Because it is mobile, deficiency symptoms appear
as necrosis or chlorosis in older leaves and/or
leaf margins.
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Sulfur - S
1. Often absorbed as SO4 2- 2. Because of its
presence in the atmosphere, it is difficult to
show S deficiency. 3. S is critical for protein
structure where disulfide bonds between cysteine
and methionine govern tertiary structure.
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Sulfur - S
4. Sulfur a constituent of thiamine, biotin,
coenzyme A. 5. Fe-S proteins are involved in
photosynthesis and N2 fixation. 6. Thiocyanates
and isothiocyanates contain S. They may improve
insect resistance but are harmful to livestock.
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• Fe
• Mn
• Cu Co-enzymes
• Zn
• Mo

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Iron - Fe
1. Often absorbed as Fe 2 2. Fe a constituent of
catalase and peroxidase 3. Deficiency shows first
as chlorosis in interveinal regions of youngest
leaves
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Iron - Fe
4. Fe 3 can form insoluble hydrous oxides
(Fe2O3 . 3H2O) at biological pH. Thus, Fe
availability in neutral or calcareous soils is
low. 5. EDTA ethylenediaminetetraacetic acid (Na
salt) can chelate Fe and make it more available.
Sometimes called Fe sequestrene.
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Manganese - Mn
1. Mn is part of a manganoprotein which critical
in the photosynthetic oxygen evolution process.
2. Deficiency can lead to the appearance of
greenish-gray, oval-shaped spot on the leaves of
young cereal plants.
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Manganese - Mn
3. Mn a cofactor for several dehydrogenase and
decarboxylase enzymes 4. Mn can often substitute
for Mg in reactions such as those involving ATP
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Copper - Cu
1. Often is absorbed as Cu2. 2. Cu is a cofactor
in several oxidative enzymes (e.g., cytochrome
oxidase) 3. Browning of cut apple and potato is
due to Cu enzymes polyphenoloxidases.
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Copper - Cu
4. Cu is a cofactor for superoxide dismutase
(SOD) which detoxifies superoxide radicals. 5. Cu
deficiency symptoms consist of stunted growth and
distorted leaves.
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Zinc - Zn
1. Often absorbed as Zn2. 2. Zn activates many
enzymes including alcohol dehydrogenase, carbonic
anhydrase, and superoxide dismutase.
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Zinc - Zn
3. Because Zn is involved with indole-3-acetic
acid metabolism, Zn deficiency symptoms are a.
shortened internodes b. small leaves
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Molybdenum - Mo
1. Often is absorbed as MoO42- . 2. Mo is a
cofactor for nitrate reductase and
dinitrogenase. 3. Deficiency symptoms include
young twisted leaves, interveinal chlorosis and
necrosis in older leaves.
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Chlorine - Cl
1. Often absorbed as Cl- . 2. Like Mn, Cl is
require for oxygen evolution. 3. Since it is
required for cell division, deficiency symptoms
include young twisted leaves. Also, interveinal
chlorosis and necrosis in older leaves can
result.
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Boron - least understood of all
micronutrients 1. Cell wall constituent with
mannose derivatives 2. Important in cell
division and elongation, stubby roots and
necrotic apical meristem may result when B is
deficient. 3. Boron deficiency leads to
increased activity of enzymes that oxidize
indole-3-acetic acid. 4. Boron deficiency can
lead to stem crack in celery and to heart rot
in sugar beets.
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Nickel - Ni
1. Ni is a component of urease and the
hydrogenase component of N2 fixation. Some seeds
contain canavanine, arginine, or ureides which
create urea when broken down. Urea is toxic
without Ni and urease. 2. To show deficiency, it
is often necessary to grow 2 or 3 generations of
plants without Ni.
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Beneficial Elements
1. Sodium - Na, required for C4 plants, perhaps
pyruvate transport 2. Silicon - Si, strengthens
cell wall in grasses, helps fight fungi,
lodging 3. Cobalt - Co, essential for legumes,
really for N2-fixing bacteria 4. Selenium -
unknown role
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Make-up of Soil

• Fragmented parent rock material of various sizes
  (sand, silt, clay)
• Organic matter (plant, animal, microbial remains)
  Organic P has low availability.
• Living micro and macro organisms
• Soil solution
• Gaseous phase (N2, O2, CO2, trace gases)

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N2 Fixation

• N is one of the more plentiful nutrients but not
  in the available form (N2)
• Several bacteria fix N in plant roots
  (primarily legumes beans, peas, soybeans,
  alfalfa, clover, etc.)
• Symbiotic relationship between bacteria and plant

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• N2
• Reduction Rx also called N2 fixation
• ATP, NADH2
• NH3
• Oxidation Rx
• NO3

Nitrification
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Mineral Uptake

• Roots and Leaves
• In ionized form
• (NH4, NO3-, K, Ca, Cl-)
• Transport
• Passive (diffusion)
• or
• Active (pumped)

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Passive Transport

• Dependent upon the electrical potential across
  membrane ( or -)
• Most cells are negatively charged on inside
• Soil particles are also negatively charged
• So positive ions (cations) are more readily bound
  to soil particles and transported across
  membranes than negatively charged ions (anions)

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Active Transport

• Uses energy usually as ATP
• Pumps against an electrochemical gradient (Nernst
  equation)
• More anions (-) use active transport that cations
  (). Why? Because the cytoplasm is more
  negative than the apoplast.

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Nernst Equation at 25 C
-58
Ci
Emv
log10
?
n
Ca
Example If electrical potential is -116 mV, K
could accumulate to 100 mM via diffusion if
outside concentration was 1 mM.
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If membranes consist of a hydrophobic layer how
do anions and cations pass through it?
Protein channels transect the hydrophobic layer
and facilitate charged particle transport.
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Ion Movement

• Ions track water movement from root hairs to the
  xylem and upward
• Symplastic movement (cell to cell, via
  plasmodesmata)
• Apoplastic movement (intercellular spaces)

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Plasmodesmata

• Connecting tubes between plasmalemma of cells
• Responsible for transport between cytoplasm of
  neighboring cells

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An Ions Pathway

• symplast
• root hair endodermis
• apoplast
• xylem
• phloem

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Ion Mobility

• Ions can be delivered anywhere for utilization
• Some can be redistributed from older tissues if
  needed (deficiency symptoms in old tissues)
• Example N from enzymes/proteins
• Mg from chlorophyll
• Some are not redistributed (deficiency symptoms
  in new tissues)
• Example Ca and Fe