Chapter 5 The nutrients translocation in the plant.

Chapter 5

The nutrients translocation in The nutrients translocation in the plantthe plant

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) 。


SymplasticApoplastic

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

根被层或表皮层外皮层

导管分子

中柱鞘

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.

It should be borne in mind that the effect of metabolism on water uptake and retention is an indirect one

Symplast 共质体 and apoplast 质外体

symplastic route (intracellular)

apoplastic route(extracellular)

‘Symplastic’ pathway

‘Apoplastic’ pathway

Part cross-section of primary root - two pathways for movement of water & nutrients

Within cells

Between cells

‘Symplastic’ pathway

The exodermis as a barrier (some species)

Uptake blocked

外皮层表皮层

早期后生木质部

末期后生木质部

皮层

中柱

韧皮部内皮层

凯氏带

SymplastSymplast 共质体共质体 and apoplastand apoplast 质外体质外体

• 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

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。


Cytosol

Vacuole

The relationships of potassium content in tissue with K concentration is cytosol and vacuolar

The effects of supplying Ca concentration on the Ca content and growth of dicotyls and monocotyledons

（ Loneragan ）Ca

concentration（ mM ）

0.8 2.5 10 100 1000

Relative growth rate

rye 43 100 94 94 93

tomato 3 19 52 100 80

Ca content （ mg/g DM ）rye 0.6 0.7 1.5 3.7 10.8

tomato 2.1 1.3 3.0 12.9 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）

• 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)


• 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.


• 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 ）

Part of plant

Supply to the cut stem

45CaCI2

45CaCI2+Ca2++Mg2+

+K++Na+

45CaCI2+root exudate

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

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.


�

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.


木质部与韧皮部之间养分转移示意图木质部与韧皮部之间养分转移示意图

P

T

X

韧皮

部

木质

部（

Xyle

m）

转移细胞（ Transfer cell ）

韧皮部（ Phleom ）

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 xylemThe 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 Composition of xylem sap in Ricinus communisRicinus communis after after applying the root exudation and the root pressure chamber applying the root exudation and the root pressure chamber

technique (Schurr and schulze 1995).technique (Schurr and schulze 1995).

Nutrients Intact plant(mol/m3) Root exudation(mol/m3) Root exudation/intactplant

K+ 6.6 17 2.6

Ca2+ 1.8 5 2.8

Mg2+ 0.7 4 5.5

NO3- 4.7 20 4.3

SO42- 0.2 1.8 7.5

PO43- 0.2 4 27.7

CI- 0.09 0.4 4.6

Gln 0.57 5 8.8

Arg 0.004 0.2 16.5

Glu 0.009 0.06 23.3

H+ 0.00031(pH6.5) 0.0036(pH5.4) 11.6

Exudation rates averaged to 20μ L/min in the root exudation technique and transpiration rate at 450μ L/min in average

• 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

The composition of xylemThe composition of xylem

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.

韧皮部 (phloem)

• 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 Composition of phloem of castor oil plant (Ricinus communiscommunis 蓖麻）蓖麻） (from Hall and Baber 1972)(from Hall and Baber 1972)

Dry matter 100-125mg/g

Sucrose（蔗糖） 234-304mol/m3

Reducing sugars（还原糖） -

Amino acids（氨基酸） 35.2 mol/m3

Keto acids(酮酸) 15-24 mol/m3

Phosphate(H2OP4-) 2.5-3.8 mol/m3

Sulphate(SO42-) 0.3-0.5 mol/m3

Chloride9CI) 10-19 mol/m3

Nitrate(NO3-) -

Bicarbonate(HCO3-) 1.7 mol/m3

Potassium(K) 60-112 mol/m3

Sodium(Na) 2-12 mol/m3

Calc ium(Ca) 0.5-2.3 mol/m3

Magnesium(Mg) 4.5-5.0 mol/m3

Ammonium（NH4+） 1.6 mol/m3

Auxin（生长素） 0.06 mol/m3

Gibberellin（赤霉素） 0.0067 mol/m3

Cytokinin（细胞分裂素） 0.052 mol/m3

ATP 0.4-0.6 mol/m3

pH 8-8.2 mol/m3

Solute potential（溶质势） -1.4—1.5MPa

Conductance（导度） 13.2mS

Viscosity(粘度) 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).

• 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 KTable K++ cycling and recycling in castor bean and NaCI- cycling and recycling in castor bean and NaCI-stressed white lupin relatively large amount of Nastressed white lupin relatively large amount of Na++ are are cycled back in the phloem to the roots (Jeschke and cycled back in the phloem to the roots (Jeschke and

Pate,1991; Jeschke,1987)Pate,1991; Jeschke,1987)

Proportion of total uptake

White lupin Caster bean path

K Na K Na

Xylem import to the leaf 96 45 138 11

Xylem export from the leaf 72 33 93 9

Phloem transport to the root 59 33 85 9

Cycling through the root 39 - 78 -

Total uptake (mmol per plant) 1.07 1.23 2.88 0.48

• 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


Model of cycling of nutrients in plantModel of cycling of nutrients in plant

pool proteins leavesleaves

xylemxylem 氨基酸 Amino acids

氨基酸 proteinspool

phloemphloem

rootroot

Soil solutionSoil solution

NO3- NH4

+

NO3-

NO3-

NO3-

NH4+

NH4+

Amino acids

Amino acids

Amino acids

Models of K cycling in the xylem and phloem with NO3

- and malate transport in plant

PEP

K +

malate pyruvate

K +NO NO

K HCO

CO2

3

3 3

+

3K+

NH3shoot

root

Malate K

phloemMalate K

xylemKNO3

NO

Redistribution of mineral nutrients in the phloemRedistribution 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.

• 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.


• 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.


• 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 mobileSlowly mobileimmobile

N ironiron B

P Mn CaK ZincZincMg Copper

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.


The deficiency symptoms of The deficiency symptoms of high reusable nutrients appears on high reusable nutrients appears on the older part of plant firstly, but the older part of plant firstly, but the symptoms of immobile nutrient the symptoms of immobile nutrient appears on the younger parts of appears on the younger parts of plants firstly.plants firstly.


氮、磷、钾和镁四种养分在体内的移动性大，因而，再氮、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。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 N,P,K and Mg is rather mobile in throughout the whole plant, so their capability of retransloction the whole plant, so their capability of retransloction and redistribution is higher. When external supply is and redistribution is higher. When external supply is inadequate, the nutrients in the older plant parts are inadequate, the nutrients in the older plant parts are mobilized and translocated via phloem into younger mobilized and translocated via phloem into younger growing tissue to cover their growth requirement.growing tissue to cover their growth requirement.


铁、锰、铜和锌通过韧皮部向新叶转移的比例及数铁、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。量随之增加。

The translocation of iron, Mg, copper and zinc via The translocation of iron, Mg, copper and zinc via phloem into younger leaves are determined the phloem into younger leaves are determined the concentration of soluble organic substances (chelate) . The concentration of soluble organic substances (chelate) . The higher is concentration of chelate, the more mobilize of higher is concentration of chelate, the more mobilize of iron, Mg, copper and zinc, and the more of them iron, Mg, copper and zinc, and the more of them translocated from older leaves to younger leavestranslocated from older leaves to younger leaves . .


maturation

anthesis

Vegetative organs

Time (after germination)

Total nutrients

seeds

禾谷类作物个体发育期间矿质养分分配的典型图解

Nutrients Parts of deficiency symptoms

Reusability

N 、 P 、 K 、 Mg Older leave mobile

S New leave Slowly mobile

Fe 、 Zn 、 Cu 、 Mo

New leave Very slowly mobile

B 、 Ca New leave on the apical

immobile


Conclude 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

• Redistribution of nutrients in plants

• Mobilization of nutrients in phloem and redistribution

• Nutrients deficiency symptom and their reusable

Conclude Conclude

Chapter 5 The nutrients translocation in the plant.

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Transcript of Chapter 5 The nutrients translocation in the plant.