Transcript NO 3

Chapter 5
The nutrients translocation in
the plant
The short distance transports of nutrients
There are two main steps nutrients
translocation in plant after nutrients absorbed
by the root. One is the centripetal transport
from the rhizoplane through the cortex tissue
of the roots towards the xylem vessels of the
central cylinder. Another one is the vertical
transport from from the root towards the
leaves.
The short distance transports of nutrients
（1）短距离运输(short distance transport) 也叫横向运
输(the centripetal transport)，或径向运输。指养分由
根的外表皮，穿过皮层进入中柱的过程。
It is the centripetal transport from the
rhizoplane through the cortex tissue of the
roots towards the xylem vessels of the
central cylinder中柱.
There are two pathways of ions transportation
in the centripetal process. 即质外体途径(Apoplastic
pathway)和共质体途径 (Symplastic pathway)。
Symplastic
Apoplastic
The apoplast (apo, greek= away from the plasma) is the continuous system
of water and air filled spaces of the cell wall and is in close contact with
the soil medium, the contact often being enhanced by numerous root hairs.
Water free space(水分自由空间） and Donnan free space（ 杜南自由空间）
Cations interact with the fixed anions in the cell wall (pectin and proteins) and hence
their motion is much restricted. The part of the apoplast is also called
apparent free space (表观自由空间）as this space appears to be free for diffusion.
‘Apoplast’: cell walls & spaces between cells
(‘intercellular spaces’); filled with ‘air’ & water
Cell walls
外皮层
根被层或表皮层
It should be borne in mind
that the effect of metabolism
on water uptake and
retention is an indirect one
中柱鞘
导管分子
Water may also travel through the root cortex via the cellular pathway
including membrane transport (transmembrane pathway) or through
plasmodesmata 胞间连丝(symplastic pathway)
The cytoplasm of one plant cell is generally connected
to the cytoplasm of neighboring cells by numerous plasmodesmata.
This cytoplasmatic continuum is called the sympalst.
Symplast共质体 and apoplast质外体
symplastic route
(intracellular)
apoplastic route
(extracellular)
Part cross-section of primary root - two pathways for
movement of water & nutrients
Within cells
‘Symplastic
’ pathway
Between cells
‘Apoplasti
c’ pathway
The exodermis as a barrier (some species)
皮层
‘Symplastic’
pathway
中柱
早期后生木质部
末期后生木质部
韧皮部
内皮层
凯氏带
Uptake blocked
外皮层
表皮层
Symplast共质体 and apoplast质外体
• However, in practice it is probably only the
outermost cells of the epidermis (including root
hairs) and cortex which take up nutrients
because of the depletion zones. Thus, by the
time that the outermost cells have removed ions
from the apoplastic solution, the concentration in
the cell wall of inner cells of the cortex must be
very low.
• Measurement
of
electrochemical
gradients in cell
profiles across the
root show that
uptake of K+ into
cells may be active
or passive, but the
final transfer into
the
xylem
is
passive.
•
CI- into cell is
active,
but
is
passive into xylem
The short distance transports of nutrients
N、P、K, Mg等养分主要以质流的方
式通过共质体(symplast)途径运输；运输
过程中，有部分养分进入液胞(Vacuole)；
Ca、Si、Na、Fe（？）主要通过质
外体(poplast)途径运输。
Ca 在运输过程中容易被细胞壁上的
负电荷吸附。
The relationships of potassium content in tissue
with K concentration is cytosol and vacuolar
Cytosol
Vacuole
The effects of supplying Ca concentration on the Ca content
and growth of dicotyls and monocotyledons （Loneragan）
Ca
concentration
（mM）
rye
tomato
rye
tomato
0.8
2.5
10
Relative growth rate
43
100
94
3
19
52
Ca content（mg/g DM）
0.6
0.7
1.5
2.1
1.3
3.0
100
1000
94
100
93
80
3.7
12.9
10.8
24.0
Long distance transport of mineral nutrients
In higher plants, an adequate transport of minerals
between sites of uptake and production (sources)
and site of consumption (sink) is essential.
The most important pathways for long distance transport are
the vascular tissue（导管组织） of the xylem（木质部）
and phloem(韧皮部）
Long distance transport of mineral nutrients
• 木质部 xylem transport
• 单向运输 unitransport: water and nutrients are
taken up from the root medium and
translocated towards the upper plants parts
by the xylem
• 装载(Xylem loading) ：K+、NO3- 、CI-等离子
为被动(passive)
Long distance transport of mineral nutrients
• 蒸腾作用（Transpiration)
• The relatively high rate of water flow along
the xylem vessels in an uptake direction
cause a rapid translocation of solutes
dissolved in the xylem vessels.
• It is generally accepted that transpiration is
the main diving force not only for water
transport, but also for nutrient
translocation in the xylem.
Long distance transport of mineral nutrients
• 离子的交换吸附 interception exchange
•
The transport mechanism for solutes
in the xylem sap is predominantly one of
mass flow, where cations and
particularly divalent cations may be
adsorbed to cell walls surfaces and
exchanged for other cations.
The effect of other cations in root exudate on the long distance
translocation of 45Ca in bean stem without root（24h）
（μe/g DM)（Jaeoby，1967）
Supply to the cut stem
Part of plant
45CaCI
2
45CaCI +Ca2++Mg2+
2
+K++Na+
45CaCI +root
2
Primary
leaves
0.04
4.7
1.8
12～18cm
stem
7
19
11
8～12cm stem
28
56
40
4～8cm stem
84
57
61
0～4cm stem
159
81
81
exudate
Long distance transport of mineral nutrients
传递细胞的作用( function of transfer cells):
Some inorganic nutrients can be taken up
rapidly from cells adjacent to the xylem vessels.
They thus decrease in concentration as they are
transported along the xylem vessels.
This is true for the major plant nutrients ,
such as NO3-, H2PO4-and K+; On the other hand,
other nutrients are absorbed relatively slowly in
the xylem sap by adjacent cells.
Long distance transport of mineral nutrients
Some Solutes in the xylem saps are
translocation from the xylem into phloem cells
through the transfer cells, and storage in the cells
or transport back to the roots.
Transfer cells along the phloem which with
their invaginations( 凹入) increase the adjacent
cell surface and thus also the lateral movement of
ions into the adjacent phloem parechyma cells.
木质部（Xylem）
韧皮部
P
X
韧皮部（ Phleom）
转移细胞（Transfer cell）
T
木质部与韧皮部之间养分转移示意图
Long distance transport of mineral nutrients
释放与分泌 (secretion)
In some plants, the NO3- concentration is
decreasing, and amino acids contents is
increasing in the sap as solutes transport from
root the shoot in the xylem.
如豆科作物，在沿木质部迁移时，NO3-N含
量减少，氨基酸含量增加
• Soil-Plant-Atmosphere continuum
Cohesion of water molecules to one another
and adhesion to xylem walls by hydrogen bonds
The composition of xylem
• The xylem sap is rather dilute solution,
which is made up largely of inorganic
ions and also of amino acids.
• Different techniques have been used in
the collection of xylem sap which have
result in variations in the ion
concentrations that have been obtained.
Composition of xylem sap in Ricinus communis after
applying the root exudation and the root pressure chamber
technique (Schurr and schulze 1995).
Intact plant(mol/m3 )
Root exudation(mol/m3 )
Root exudation/intactplant
K
6.6
17
2.6
Ca2+
Mg2+
1.8
0.7
5
4
2.8
5.5
-
4.7
0.2
20
1.8
4.3
7.5
PO4
CI-
3-
0.2
0.09
4
0.4
27.7
4.6
Gln
0.57
5
8.8
Arg
0.004
0.2
16.5
Glu
H+
0.009
0.00031(pH6.5)
0.06
0.0036(pH5.4)
23.3
11.6
Nutrients
+
NO3
SO4 2-
Exudation rates averaged to 20μ L/min in the root exudation technique and
transpiration rate at 450μ L/min in average
The composition of xylem
• The factors which impact on the amplitude of
the diurnal pattern:
• Transpiration
nutrient uptake (K+)
Lateral exchange of cations (Ca2+)
• Taken up by the cell adjacent cells to the
xylem vessels(H2PO4- and K+)
• Phloem cycling
韧皮部(phloem)
The phloem is the tissue that mainly
translocates organic compounds, the
products of photosynthesis and amino acids
from mature leaves to areas of growth and
storage driven by a turgor pressure gradients.
韧皮部(phloem)
Phloem-mobile mineral nutrients are
also transport in the phloem and are
transported both in an upward and
downward direction----bidirectional.
Basically the transport in the phloem
is driven by a turgor pressure gradient
from the source area of plant with low
solute potential to several sink areas with
a high solute potential.
• The phloem comprises of a number
of different cell types of which the
sieve elements (SE) and companion
cells (CC) are the most important.
These are living cells although SE
have lost some organelles (e.g. the
vacuole) and others are modified
(e.g. mitochondria and plastids).
•
• The SE and CC are connected by
plasmodesmata (modulated pores
connecting the cytosols of adjacent
cells). The SE form the translocation
pathway and are separated by a
sieve plate containing pores. A
collection of SE forms a sieve tube.
Composition of phloem of castor oil plant (Ricinus
communis蓖麻） (from Hall and Baber 1972)
Dry matter
Sucrose（蔗糖）
Reducing sugars（还原糖）
Amino acids（氨基酸）
100-125mg/g
234-304mol/m
3
35.2 mol/m3
3
Keto acids(酮酸)
Phosphate(H2 OP4 -)
15-24 mol/m
2.5-3.8 mol/m3
Sulphate(SO4 2-)
0.3-0.5 mol/m3
Chlor ide9CI)
10-19 mol/m
Nitrate(NO3 -)
3
-
3
Bicarbonate(HCO3 )
1.7 mol/m
Potassium(K)
Sodium(Na)
60-112 mol/m
2-12 mol/m3
Calc ium(Ca)
Magnesium(Mg)
0.5-2.3 mol/m
4.5-5.0 mol/m3
Ammonium（NH4 +）
1.6 mol/m3
Auxin（生长素）
Gibberellin（赤霉素）
0.06 mol/m
0.0067 mol/m3
Cytokinin（细胞分裂素）
0.052 mol/m
ATP
0.4-0.6 mol/m
pH
Solute potential（溶质势）
8-8.2 mol/m3
Conductance（导度）
Viscosity(粘度)
3
3
3
3
3
-1.4—1.5MPa
13.2mS
1.34cP at 20℃
Cycling of mineral nutrients between phloem and xylem transport
The phloem and the xylem are not directly linked
to one another. Thus in the translocation between two
pathways, water and solutes must pass through the
connecting tissues (such as transfer cell). Phloem
absorbs water from the surrounding tissues which in
turn obtain water from xylems.
On average about 5% of water transported in an
upward direction in the xylem is retranslocated via
phloem to the lower plant part(Zimmermann,1969).
Cycling of mineral nutrients between phloem and xylem transport
• Research in the last decade has shown that
continuous nutrients cycling i.e. the
retranslocation of nutrients in phloem from the
shoot to the root and the cycling i.e. the
translocation of cycled nutrients back in the xylem
to the shoot is of great importance for nutrients
which show a high phloem mobility, such as for
nitrogen and potassium, phosphorus, sulphur and
magnisium (Marschnaer, 1996,1997)
Table K+ cycling and recycling in castor bean and NaCIstressed white lupin relatively large amount of Na+ are
cycled back in the phloem to the roots (Jeschke and
Pate,1991; Jeschke,1987)
Proportion of total uptake
path
White lupin
Caster bean
K
Na
K
Na
Xylem import to the leaf
96
45
138
11
Xylem export from the leaf
Phloem transport to the root
72
59
33
33
93
85
9
9
Cycling through the root
Total uptake (mmol per plant)
39
1.07
1.23
78
2.88
0.48
Cycling of mineral nutrients between phloem and xylem transport
• Major function of the cycling
• Cover nutrient root demand for root growth (N
and S).
• Driven force in the xylem and phloem (K)
• Counteraction of toxic ion in source leaves
(CI)
• Maintainance of cation-anion balance (K and
organic acids)
• Act as signal to control nutrients uptake
pool
NO3-
NH4+
xylem
NO3-
pool
NO3-
NH4+
NO3-
NH4+
Amino
acids
Amino
氨基酸
acids
proteins
Amino acids
Amino
氨基酸
acids
proteins
leaves
phloem
root
Soil solution
Model of cycling of nutrients in plant
CO
PEP
Malate K
K
+
phloem
Malate K
HCO
K+
NO
malate
NH
K
+
shoot
NO
xylem
KNO
pyruvate
root
K+
NO
Models of K cycling in the xylem and phloem
with NO3- and malate transport in plant
Redistribution of mineral nutrients in the phloem
• As leaves and root age, some of their nutrients
are set free and retranslocated to the young
growing leaves, roots, fruits, or storage organs.
• Redistribution is remobilization and the phloem
translocation of nutrients from source leaves.
• It occurs under nutrients deficiency, during leaf
senescence or in perennial plants in spring
when nutrients are mobilized from the stem or
root.
Redistribution of mineral nutrients in the phloem
• Not all nutrient elements retranslocation with
equal case.
• The retranslocation of plant nutrients via
phloem under nutrient deficiency depends
much on the capability of sieve tubes to take
up nutrients rapidly.
• The difference of ions in phloem mobility is
also reflected in appearance of deficiency
symptoms.
Redistribution of mineral nutrients in the phloem
• As the Ca supply to a plant organ mainly
depends on transpiration intensity, the
transpiration rate of a given plant organ
is of particular importance in determining
its Ca concentration. Where transpiration
is low, Ca supply may be inadequate and
Ca deficiency may thus result.
Redistribution of mineral nutrients in the phloem
• Fruit and storage organs generally have a
lower transpiration rate than leaves. This
gives rise to blossom end rot(脐腐病） in
tomatoes, bitter pit in apples and
blackheart in celery.
Relative mobile of mineral nutrients in the phloem
mobile
Slowly mobile immobile
N
iron
B
P
Mn
Ca
K
Zinc
Mg
Copper
Nutrients reusable and the deficiency symptoms
Calcium is immobile in the phloem
because Ca loaded into the sieve
elements is inhibited, or Ca is deposited in
the phloem by the high concentration
Phosphate. The reason of Boron immobile
in the phloem is uncertain.
Nutrients reusable and the deficiency symptoms
• The nutrients in any organs of parts of
plant could be translocated to other organs
or parts via phloem, and be reused, which
is called reusable. The nutrient reusability
is dependent on the capacity of its
movement in the phloem. Such as N, P
and K are mobile in the phloem, so they
are the most reusable, but Ca and B are
immobile in phloem and the lowest
reusable.
Nutrients reusable and the deficiency symptoms
The deficiency symptoms of high
reusable nutrients appears on the older
part of plant firstly, but the symptoms
of immobile nutrient appears on the
younger parts of plants firstly.
Nutrients reusable and the deficiency symptoms
氮、磷、钾和镁四种养分在体内的移动性大，因而，再
利用程度高，当这些养分供应不足时，可从老部位迅速及时
地转移到新器官，以保证幼嫩器官的正常生长。
N,P,K and Mg is rather mobile in throughout
the whole plant, so their capability of retransloction
and redistribution is higher. When external supply is
inadequate, the nutrients in the older plant parts are
mobilized and translocated via phloem into younger
growing tissue to cover their growth requirement.
Nutrients reusable and the deficiency symptoms
铁、锰、铜和锌通过韧皮部向新叶转移的比例及数
量还取决于体内可溶性有机化合物的水平。当能够螯合
金属微量元素的有机成分含量增高时，这些微量元素的
移动性随之增大，因而老叶中微量元素崐向幼叶的转移
量随之增加。
The translocation of iron, Mg, copper and zinc via
phloem into younger leaves are determined the
concentration of soluble organic substances (chelate) . The
higher is concentration of chelate, the more mobilize of iron,
Mg, copper and zinc, and the more of them translocated
from older leaves to younger leaves.
Total nutrients
maturation
anthesis
seeds
Vegetative organs
Time (after germination)
禾谷类作物个体发育期间矿质养分分配的典型图解
Nutrients reusable and the deficiency symptoms
Nutrients
Reusability
N、P、K、Mg
Parts of deficiency
symptoms
Older leave
S
New leave
Slowly mobile
Fe、Zn、Cu、Mo
New leave
Very slowly mobile
B、Ca
New leave on the
apical
immobile
mobile
Conclude
• There are two steps of nutrients
translocation in plant: short distance and
long distance transport
• Apoplast pathways and symplast
pathways in short distance transport
• Xylem and phloem in long distance
• Unidirectional transport in xylem and
bidirectional transport in phloem
• Cycling of mineral nutrients between
phloem and xylem transport
Conclude
• Redistribution of nutrients in plants
• Mobilization of nutrients in phloem and
redistribution
• Nutrients deficiency symptom and their
reusable