Plant Mineral Nutrition

• Epstein E & Bloom AJ.
Mineral Nutrition of Plants: Principles and
Perspectives
. 400 pages


1.2 Improving quality
of product through
plant nutrition
Deformed fruit caused by Boron deficiency
normal
deficient
Improving quality

increasing protein
content of cereals through high N
low
moderate excess
Grain yield
P
r
o
t
e
i
n
y
i
e
l
d
Protein %
Grain Yield
or
Grain Protein Yield
or
Grain Protein %
Availability of nitrogen
Yield
% protein
Nitrogen applied
Low protein
low yield
Excess N
high yield
high protein
Max yield
10.5 - 11%
protein
Wheat quality
1.3 Improving Human Nutrition
Low nutrient concentrations in food can cause
severe deficiencies in humans and farm animals.
Main micronutrient deficiencies worldwide
•Iron
•Zinc
• Iodine -
not essential for plants
• Selenium -
not essential for plants
• Vitamin A - not essential for plants
Micronutrient deficiency in 190 soils
worldwide
0
20
40
60
Zn Cu Mn Fe
% def i ci ent
Global prevalence of iron deficiency anaemia
0
10
20
30
40
50
% anaemic
1980 1990
Year
– impairs learning and growth
– diminishes ability to fight infections
– maternal & foetal illness or death
Fe deficiency
Macronutrients can also be deficient in foods
Malformation in children due to
insufficient Calcium in diets.
Grains – low in Ca
Vegetables – high in Ca
Malnutrition
“O” shape or “X” shape legs
2 Essential elements for plant
2.1 Elements in plant
Fresh sample
Dry matter
Killing
105
°C
30 min
75
°C
24-48 h
Drying
Ashing
600
°C
Gas
Ash
100
1-5
(on dry wt base)
10-20
C

CO
2

H

O

H
2
O

N

NO
x

S

H
2
S

SO
2

A little N
Most S
All metal and non-volatile elements:
more than 60 kinds
Gas
Ash
Please refer to P33
Classification of the ash elements
1. Essential Elements
2. Beneficial Elements
3. Non-essential Elements

Different in different plant
species or cultivars.
hydrophytes < 1%, halophytes
>
5%

Leaf >other parts

Older parts >younger parts.

Xylem is lowest part for mineral element
contents.
Some general characteristics
1. Criteria for plant essential elements
2. Methods for identifying plant essential
elements
3. Kinds of plant essential elements
2.2 Plant essential elements and its identification
The elements, in brief, is necessary for plants to grow
and develop.
Three criteria (Arnon and Stout, 1939):
1. A deficiency of the element makes it impossible for
the plant to complete a normal life cycle.
不可缺失性
2. The deficiency is specific for the element in question.
不可替代性
3. The element is directly involved in the nutrition of
the plant, for example, as a constitute of an essential
metabolite or required for the function of an enzyme
system.
直接性
Criteria for plant essential elements
• The element is part of a molecule that is an
intrinsic component of the structure or
metabolism of a plant.
• The plant can be so severely deprived of the
element that it exhibits abnormalities in its
growth, development, or reproduction-that
is, its “performance”-in comparison with
plants not so deprived.
Two criteria (by Epstein, 2005):
How to test?
Plants are grown with
the element of interest
omitted from the
formulation of the
culture medium, or
present in inadequate
amount or
concentration

N
Control

Water (solution ) culture or hydroponics
(溶液培养法
——
水培法
)

Sand culture (
砂培法
)
Methods for identifying plant essential elements
Solution culture & sand culture
Be careful

1. Choosing optimum cultural solution;
2. Renewing cultural solution and adjusting pH
in time

3. Airing

4. Keeping root in darkness
5. Considering the nutrient contained in seeds
Theory

Study for function of the elements and
mechanism of its absorption.
Application:
production for vegetable, flower and
food in greenhouse, desert etc.
Kinds of plant essential elements
Macronutrients (Macroelements)
The elements are in large quantity required by plants and are
higher contents

>0.1%)
in plant body, including:
C

Carbon
H

Hydrogen
O

Oxygen
N

Nitrogen
P

Phosphorous
K

Potassium
Ca

Calcium
Mg

Magnesium
S

Sulphur.
Micronutrients(Microelements)
The elements are in small quantity required by plants and
are lower contents

<0.01%)
in plant body, including:
Fe

Iron
Cu
— Copper
Mn
—Manganese
Mo
—Molybdenum
B
—Boron
Cl
—Chlorine
Zn
—Zinc
Ni
—Nickel
Relative amounts of essential elements in plant tissues
3. Nutrient absorption
Sites for nutrient absorption
Roots
Leaves
Division and
elongation zone
Nutrient uptake steps
nut
Movement through soil
Cell wall Cell membrane
Cell to cell transport
vascular tissue
unloading
nutrient
Root
• The concept of rhizosphere
• Movement of nutrients to root surface
• Pass the membrane
- Passive transport
- Active transport
• Transport pathways
• Leaf uptake
• Factors affecting nutrient uptake
Plants obtain mineral nutrients from soil
Soil varies in
•pH
• structure
• nutrient composition
• moisture content
• microbial activity
Red Soil
Black Soil
3.1 The rhizosphere
Rovira 1960
• Layer of soil surrounding the
growing root that is affected by
the root
• Usually a few mm wide, up to
say 1 cm (no sharp boundary)*
• Extent depends on plant
properties; e.g.
- Root hair length & density
- Rhizodeposition
(exudates etc)
- Nutrient uptake versus supply
Width not to scale
* ‘Mycorrhizospheres’ can extend
many cm
Outer rhizosphere
500-5000 μm
Inner rhizosphere
10-500 μm
Rhizoplane
0-10 μm
Root
The rhizosphere: some conventions
But defined ‘phases’ may not be helpful because of
gradients (no sharp boundaries)
Gradients in the rhizosphere
Longitudinal & lateral gradients
important for plant nutrition:
- concentrations & composition
- population density & composition
- especially in waterlogged soils
- especially soil bacteria
- especially mycorrhizal fungi
Römheld 1986
200 kg N/ha
Effect of N form on the rhizosphere pH of barley
NO
3
-
NH
4
+
H
+
uptake (or
OH
-
release)
during NO
3
-
assimilation
H
+
release
during NH
4
+
assimilation
P depletion zones in the rhizosphere of maize
and rape: influence of root hairs
Hendriks et al. 1981
Distance from root surface (mm)
Isotopically
exchangeable P
(μg ml
-1
)
150
100
50
13
2
Mean root
hair length
Canola
Maize
Bulk soil
Accumulation of calcium & magnesium in
rhizosphere of barley
0 5
10 15
Distance from root surface (mm)
15
10
5
Available
Mg (mM)
75
50
25
Mg
Ca
Available
Ca (mM)
Roussef & Chino 1987
Many soil microorganisms
utilise root exudates.
Microorganisms can be
beneficial (e.g. improving
nutrient availability) or
harmful (e.g. competition for
soil nutrients, or root
disease)
mucilage
Gradients in root exudates and microorganisms
Roots are the main
structures for
nutrient uptake
1
2
3
Soil
Root
地上部

1
、截获
2
、质流
3
、扩散)
Interception and contact exchange
Mass-flow
Diffusion
3.2 Movement of nutrients to the root surface
Interception
root
soil
CO
2
+H
2
O
H
2
CO
3
H+ HCO
3

K
+
SO
4
+
root
soil
K
+
SO
4
+
H
+
HCO
3

Ion exchange in solution
Ion exchange by contact
Generally Less than 1%
• Mass-flow:
Solutes are transported with the convective flow of
water from the soil to plant roots.
The amount depends on:
the rate of flow, water
consumption of the plant and the average nutrient
concentration in the water.
• Diffusion:
Ion is transported from a higher to a lower
concentration by random thermal motion.
Directions: depends on the concentration gradient
The contribution of different ways of supply
Supply(kg/ha)
Nutrient
Nutrient in
soil(kg/ha)
Total uptaken
(kg/ha)
Interception Mass-flow Diffusion
Ca 4000 45 40 90 _
Mg 800 35 8 75 _
K 300 110 3 12 95
P 100 30 1 0.12 28.9
N 500 190 2 150 38
*
根据
Baeber

1974
)估计,根容积等于土壤容积的
1%
Pore system of the Apparent Free Space.
DFS, Donnan Free Space; WFS, Water Free Space
Micropore
Macropore
Indiffusible
anions
Cation
Anion
WFS
DFS
Rhizodermal cell wall 500-3000
Cortical cell wall 100-200
Pores in cell wall <5
Sucrose 1.0
Hydrated ions
K
+
0.66
Ca
2+
0.82
Diameter (nm)
The pores themselves would thus not be expected to offer any
restriction to movement of ions in the free space
Nutrient ions can enter the APS by Mass-flow, Diffusion and
Electrostatic binding
Cell membranes are highly selective
The basic structure of a cell membrane is the
phospholipid bilayer
, which has very low
permeability to most nutrients.
Uptake is made faster by
transport proteins
embedded in the membrane.
3.3 Passing cell membrane
10
-2
10
-4
10
-6
10
-8
10
-10
P
cm/s
Cl
-
K
+
Na
+
H
2
O
Ethanol
Boron
Cl
-
K
+
Na
+
Boron
H
2
O
Ethanol
Lipid Bilayer
Biological Membrane
MEMBRANE
PERMEABILITY
Cell membranes
• allow for controlled intracellular environment
• structure based on hydrophilic-hydrophobic interaction of
phospholipids with aqueous phases
• contain approx. 50 % protein
whose function is probably
mostly transport
• high permeability to molecules that are:
small e.g. O
2
lipid soluble e.g. ethanol
non-polar e.g. urea
• low permeability to ions e.g. K
+
, NO
3
-
• very low permeability to
di
valent ions e.g. Mg
2+
, SO
4
2-
Fluid mosaic model
, Singer & Nicolson,1972
Movement of molecules across
membranes
4
mechanisms
1. Diffusion directly through the lipid bilayer
2. Transport via carrier proteins
3. Transport through ion channels
4. Active transport
- ATPases
- co-transport
Facilitated
diffusion
Passive
transport
from Knox, Ladiges & Evans
molecule to be transported
channel
protein
carrier
proteins
extracellular
space
lipid
bilayer
cytoplasm
simple
diffusion
channel-mediated
transport
carrier-mediated
transport
energy
electrochemical
gradient
passive transport
(facilitated diffusion)
active transport
Types of Membrane Transport Mechanisms
Facilitated Diffusion

Three Essential Characteristics:

Specific (selective for single nutrient molecule)

Passive (requires no input of energy)

Saturates (non-linear dependence on concentration)
Driving forces for membrane transport
:
concentration differences
Molecules will diffuse until the
concentration is the same everywhere
Solutes diffuse throughout carrier (conformation)
in single direction.
Higher solute concentration
lower solute concentration
D
if
f
u
s
io
n
d
ir
e
c
t
i
o
n
K
+
K
+
K
+
K
+
Plasmatic
membrane
sensor
Integrate
protein
K
+
K
+
K
+
SO
4
-
K
+
K
+
K
+
K
+
K
+
SO
4
-
SO
4
-
SO
4
-
outer
inner
Ion
Channel
transport
gate
The gate can controlled by
voltage or ion concentration,
even by light, hormones or
other stimuli
Active Transport
• Requires input of energy
•For
uncharged substances
active transport
moves molecules
against their concentration
gradients

Enables cells to accumulate molecules to
higher concentrations than in the extracellular
fluid.
ATP
ATP
ATP
Driving forces for membrane transport
:
metabolic energy
Active Transport
• Requires input of energy
• For uncharged substances active transport moves
molecules against their concentration gradients

Enables cells to accumulate molecules to higher
concentrations than in the extracellular fluid.
• For charged substances (ions),
active transport moves
molecules against concentration + electrical gradients
K
+
Cl
-
Zn
2+
Mn
2+
Mg
2+
NO
3
-
NH
4
+
PO
4
-
Ni
2+
Cu
2+
SO
4
2
-
Fe
3+
Ca
2+
Fe
2
+
B
OH
OH OH
All essential mineral nutrients are
absorbed as ions except boron
Therefore all nutrients except Boron need membrane transporters
Voltages across membranes
• All cells have voltage differences across their membranes
(commonly in the range –50 to – 200 mV)
• This voltage can be used to drive membrane transport
• The voltage is mainly generated by pumping of ions
membrane voltage = membrane electrical potential = PD
V
V
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
Driving forces for membrane
transport:
VOLTAGE
0 mV
-120 mV
Negative membrane voltage will cause:
• Accumulation of cations
• Depletion of anions
What happens when electrical and concentration
differences oppose each other?
The NERNST equation:
E (mV) =
RT
zF
ln
C
o
C
i
x
Simplified version:
E (mV) =
60
z
x
log
C
0
C
i
R = gas constant
(8.31 J K
-1
mol
-1
)
T =
o
K
z = valence (e.g. +1, -2)
F = Faraday’s constant
96,500 J mol
-1
C
o
= external concentration
C
i
= internal concentration
(E = electrical potential difference
or voltage across the membrane)
Nernst Equation
Principles
:
A neutral
solute will distribute itself so that at
equilibrium,
concentrations are equal
(including across membranes)
A charged solute (ion) will di
stribute itself according
to both
concentration differences and electrostatic
attraction to
surfaces or regions of opposite charges
The Nernst equation
predicts the concentration of ions
at
electrochemical equilibrium
Na
+
1 mM 10 mM
-60 mV
Predicting direction of passive movement
E (mV) =
60
z
x
log
C
0
C
i
Cl
-
1 mM 10 mM (observed)
0.1 mM (predicted)
Distribution of ions in roots grown in nutrient medium
external
concentration
(mM)
cytoplasmic
concentration
(mM)
accumulation
ratio
K
+
0.5 90 180x
Na
+
1 10 10x
Ca
2+
1 0.1 0.1x
Mg
2+
0.5 2 4x
Cl
-
1 10 10x
PO
4
-
0.1 10 100x
NO
3
-
155x
pH 5.5 7.5 (0.01)
total osmotic solute (approx.)
20 300 15x
Distribution of ions in roots grown in nutrient medium
external
concentration
(mM)
cytoplasmic
concentration
(mM)
Predicted concentration
at –120 mV
K
+
0.5 90 50
Na
+
1 10 100
Ca
2+
1 0.1 10,000
Mg
2+
0.5 2 5,000
Cl
-
1100.01
PO
4
-
0.1 10 0.001
NO
3
-
150.1
pH 5.5 7.5 3.3
active uptake
active uptake
active uptake
active uptake
active efflux
active efflux
active efflux
active efflux
Energetic considerations - Cations
Mn
2+
Mn
2+
Cu
2+
Zn
2+
Co
2+
Cd
2+
X
2+
-120
mV
X
2+
ATP
Cations are attracted into the
cell by the negative membrane PD.
Uptake of nutrient cations theref
ore does not generally require energy.
Efflux of cations from the cell usuall
y requires energy (i.e. active transport)
Energetic considerations - Anions
Anions are repelled from the
cell by the negative membrane PD.
Uptake of nutrient anions theref
ore generally requires energy, in most
cases provided by the electrochemical gradient for H
+
(H
+
-cotransport)
Efflux of anions from the cell usually does not requires energy and may
occur through ion channels.
H
+
-120
mV
ATP
H
+
H
+
NO
3-
PO
4-
Cl
-
SO
4-
Cl
-
Two types of active transport
1. ATPase
(e.g.
H
+
-ATPase, Ca
2+
-ATPase)
in opposite directions
Antiport
Both molecules move
in same direction
Symport
2. Co-transport
cytoplasm
ext. medium
ATP
ADP + Pi
H
+
Neutral Acidic
• regulates intracellular pH
• generates membrane PD
- drives co-transport
• acidifies external medium
Energy costs for ion uptake in roots of Carex diandra
(Werf et al., 1988)
52
40
25
Maintenance of biomass
38
43
39
Growth
10
17
36
Ion uptake
80
60
40
Plant age (days)
Proportion of total ATP
demand required for
The properties of different types of
trans-membrane transport
Yes
Yes
No
Saturated
Yes
Yes
No
Specificity
Uphill
Uphill
Downhill
Direction
Yes
No
No
Energy
Protein
Protein
Lipids
Components
Active
transport
Facilitated
diffusion
Simple
diffusion
Property
M
2+
(Ca )
2+
K
+
K
+
M
2+
K
+
(KORC)
(KIRC)
(DACC)
(VICC)
(HACC)
(IRT1)
(ZIP-n)
Fe
2+
Zn
2+
Fe
2+
Fe -PS
3+
(Mn )
2+
(Mn )
2+
(Zn )
2+
(Cu )
2+
nH
+
nH
+
nH
+
nH
+
nH
+
nH
+
(Nramp-n)
PO (MoO )
44
--
SO (MoO )
44
2- -
Cl (NO )
- -
3
NO (Cl )
3
--
MoO
4
-
Cl
-
Cl
-
NH
4
+
NH
4
+
ATP
ATP
H
+
HBO
33
HBO
33
NO
3
-
1
2
3
4
5
6
7
8
10
11 12
13
14
15
16
17
18
Ca
2+
9
19
20
21
A
-
ATPases
Cation channels
Anion channels
Uniporters
Cation cotransporters
Anion cotransporters
Putative
plasma membrane
transporters