Chapter V

Energy and Material metabolisms in plant

Section 2 Water metabolism

The importance of water in plant life

1.Water content and its states in plant

Water content in plant is about 70% ~90%

It always depends:

⑴ in different plant species:

e.g. water hyacinth ( 水浮莲 )>90% lichen ( 地衣 ) only 6%

⑵ The same plant in different growth enviroments:

e.g. shade plants > arid and sunbaked plants

⑶ in different organs of the same plant

e.g. seedling > bole ( 树干 ) > dormant bud > dormant seed

70~90% 35~70% 40% 5~15%

Bound water: is absorbed by the components of protoplasm a

nd can not move freely.

Free water: isn’t absorbed , can move freely, participate in

metabolism and is used as solvent for different metabolisms.

The ratio of bound water to free water is one of the physiological

indexes indicating growth situation and resistance of plant to

adverse growth conditions.

States : bound water and free water

2. Physiological and ecological roles of water in plant

physiological action:

⑴ a main constituent of protoplasm

⑵ substrate for plant metabolism,

e.g. photosynthesis and respiration

⑶ a good solvent for absorption and transportation of substances

⑷ maintain the natural shape of plant

⑸ adequate water is required for cell division and the growth

ecological roles ：⑴ Adjusting plant temperature

High specific heat ( 比热 ) — maintain constant temperature

High heat of vaporization （高汽化热）— reduce plant temperature

to prevent the harm

High dielectric constant （介电常数）— is good for ionic dissolution

⑵ Water has high permeability to visible light

⑶ Water adjusts the plant living environment

Water potential (ψw ) 水势：

The potential energy of water per unit volume relative to p

ure water in reference conditions. Water potential quantifies t

he tendency of water to move from one area to another due to

osmosis, gravity, mechanical pressure such as surface tension.

Definition of water potential

一个系统中，水的总能量中可以用于作功的能量

（自由能）的大小即为水势。

Generally, the water potential of pure water at an atmosphere

and 0 ℃ is defined as 0 Pa.

When there have some solutes, the solute particles in solvent c

an reduce the free energy of water. So the free energy in solutio

n is lower than that of pure water.

The value of water potential is negative, and the denser its conc

entration is, the lower its water potential will be.

通常将纯水在 1个大气压和 0℃下的水势定为 0 Pa ，当水中有溶质存在时，溶液中的溶质颗粒降低了水的自由能，所以溶液中水的自由能要比纯水低，溶液的水势为负值，溶液越浓，水势越低。

Water potential of plant cell

Water move in or out from cells following the gradient o

f water potential. Plant cells are a complicated system, its wat

er potential is determined by several factors, including:

⑴ solute potential, (ψs ) 溶质势 its value is always negative

⑵ pressure potential, (ψp) 压力势 mostly positive

⑶ matrix potential, (ψm) 衬质势 always negative

Ψw = ψs + ψp +ψm

Ψw = ψs + ψp ( when have a mature vacuole )

ψw== ψm ( dry seed )

Solute potential ( ψs ) 溶质势 / 渗透势 : also named as osmotic

potential. is due to the existence of solute that reduce the fre

e energy of water, so its value is lower than that of pure wate

r. Value is negative.

由于溶质颗粒的存在降低了水的自由能，因而其水势低于纯水

的水势。 恒为负值 .

Osmosis 渗透作用

Semipermeable membrane

Sweet water

Pure water

Osmosis ： water move from a hypotonic ( 低渗 )system to a hy

pertonic ( 高渗） system through a semipermeable membrane

Ψw values for several common compounds

solution Ψw / Mpa

Pure water 0

Hoagland nutrient solution -0.05

seawater -2.50

1mol·L-1 sucrose -2.69

1mol·L-1 KCl -4.50

The protoplasm layer, including plasma m

embrane, protoplasm and vacuole membra

ne, of a mature cell is to be equivalent to a s

emipermeable membrane.

Thus vacuolar sap (cell sap) and extracellu

lar fluid constitute an osmotic system due to

the semipermeable membrane role of proto

plasm.

A plant cell is a kind of osmosis system

protoplasm layer

water transport between plant cells （ Ψw ， MPa ）

A

-0.8

B

-0.6

C

-0.4

1.When in a higher Ψw solution, a cell will soak up water.

2 ） When in a lower Ψw solution, cell will dehydrate.

3 ） When in a solution with equal water potential, cell will soak and dehydrate the same quality of water.

Water always move from a hig

her water potential system to a

lower water potential system,

untill their water potentials ar

e same.

Pressure potential (Ψp ) 压力势

由于细胞壁压力的存在而引起的水势增加值。

一般情况下，压力势为正值； 质壁分离时，压力势为零；

cell with turgor pressure cell with decreased turgor pressure

Matrix potential (Ψm) 衬质势：

衬质是指表面能够吸收水分的物质（蛋白质 、淀粉 、 纤

维素）。由于细胞胶体物质亲水性和毛细管对自由水的束缚而引起的水势降低值。 恒为负值

未形成液泡的细胞有一定的衬质势（如干燥种子），已形成液泡的细胞衬质基本为水饱和，衬质势绝对值小（趋于零），可忽略不计

故具有液泡的成熟细胞，其水势可简化为：

Ψw = Ψs + Ψp

（ 水势 = 渗透势 / 溶质势 + 压力势）

Water absorption of plant cell

植物细胞对水分的吸收※

吸

水

方

式

water imbibition 吸胀性吸水（未形成液泡的细胞）

即吸胀作用。通过细胞中亲水胶体吸水膨胀的现象

Osmotic water absorption 渗透性吸水（具液泡的成熟细胞）

最主要的吸收方式

metabolic water absorption 代谢性吸水（直接耗能）

耗能跨膜吸收有机溶质和无机离子以增加渗透势方式

Water absorption in plant root system (active and passive ）

Plant root uptakes water from outside environment just due to the metabolic activity of plant root system.

Mechanism: The metabolic activity of roots causes ion transporta

tion and absorption, then induces a difference water potential whi

nin or without plant cells. It pushes water goes through epidermis,

cortex and endoderm and goes into stele vessel from outside enviro

nment, and then transports upword in plant.

Active water absorption

Root pressure: a kind of power generated in plant root system

which make liquid stream transport from root to shoot. Root pr

essure is caused by active transport of mineral nutrient ions into

the root xylem. Without transpiration to carry the ions up the st

em, they accumulate in the root xylem and lower the water pote

ntial. Water then diffuses from the soil into the root xylem due t

o osmosis. Root pressure provides a force, which pushes water u

p the stem, but it always less than 0.1MPa and can only make w

ater column up about 10m.

Active water-absorption behaviours:

root pressure, bleeding and guttation.

root pressure

Bleeding: bleeding sap, determine the size of root pressure. Gut

tation: The exudation of water from leaves as a result of root pr

essure. Sufficient soil moisture ， wet weather ， lower trans

piration , apex of leaf or edge of leaf.

Two evidences for existance of the plant root presure.

Active water-absorption behaviours:

root pressure, bleeding and guttation.

Guttation from barley plant leaves

（ hydathode ）

bleeding

Root pressure is studied by removing the shoot of a plant near the soil level. Xylem sap will exude from the cut stem for hours or days due to root pressure. If a pressure gauge ( 压力计 ) is attached to the cut stem, the root pressure can be measured.

2 、 Passive water-absorption in plant root system

Roots absorb water due to the transpiration of stem and leaf.

evidence ： an ongoing stem and leaf transpiration can absorbs

water from anaesthetized ( 麻痹的 ) or dead root. Root is only be

used as a surface for passive absorption. The transpiration

drafting causes a decrease in root water potential and promotes r

oot absorb water from soil passively.

Transpiration: a process that water in plant body emits from p

lant surface as a gaseity style. This is the main water-absorption

way for plant.

cuticular transpiration (≤5%) 角质层蒸腾

stomata transpiration (95%) cuticular 气孔蒸腾Two ways

Under the same conditions, Whether 1mm2

area of free water or 1mm2 area leaf with

many stomatas have the same quantity of

transpiration ？

3 、 Mechanism of stomatal transpiration —alveolus diffusion （小孔扩散）：

Diffusion rate of gaseity water through alveolus surface is

n’t directly proportional to the area of alveolus, but is directly p

roportional to the perimeter of alveolus.

气体通过小孔表面扩散的速率不与小孔的面积成正比，而

是与小孔的周长成正比。

Ralative area of a

lveolus

小孔相对面积

Ralative perimeter

of alveolus

小孔相对周长

Ralative quatity of

diffusion loss

扩散失水相对量

1.00

0.37

0.05

0.01

1.00

0.61

0.21

0.13

1.00

0.59

0.18

0.14

一个大孔分散为许多小孔 ,总面积相等时 ,周长增加数十倍 , 扩散速率增大 ;

气孔间距为其直径的 10倍左右 , 扩散水分子间相互干扰最小 , 边缘效应最大。

when a big hole is scattered into a number of small holes an

d gross area is the same, the perimeter will increases almost 10

times and the diffusion rate will also increase greatly. Stomatal space is about 10 times of its diameter, and will ha

ve the smallest interfere between each diffused water molecule

and have the biggest edge effect.

Transpiration rate through stomata

The area of stomata is always less than 1% that of the leaf area,

but the transpiration quantity through stomata is about 50% of t

he quantity through plant leaf .

气孔面积一般不超过叶面积的 1% ，但通过气孔的蒸腾量却达到叶片同样面积的蒸发量的 50% 以上。

Alveolus diffusion law

Mechanism of stomatal movement:

Stomata can move —— open on daytime and close at night 。

Reasons for opening and closing —— regulated by the water potential of guard cells in leaves.

stomatal movement hypothesis:

1 ） starch-sugar conversion theory ( 淀粉—糖转化学说 )

2) inorganic ion uptake theory ； K+ ( 无机离子吸收学说 )

3) malate production theory ( 苹果酸生成学说 )

Mechanism ： osmoregulation of guard cells

—— imbibition and shrinkage

Starch-sugar conversion theory

illumination

photosynthesis in guard cells

Consume CO2, pH rise

Hydrolysis activity of amylophosphorylase rise

Starch is hydrolyzedto G-1-P

Decline of water potential

Guard cells turgor pressure increase

Stomatas open

darkness

respiration in guard cells

Produce CO2, pH decline

Synthesis activity of amylophosphorylase rise

G-1-P is synthesized to Starch

Increase of water potential

Guard cells turgor pressure decline

Stomatas close

Malate production theory

Illumination/darkness

Photosynthesis/ respiration in guard cells

Produce ATP and malic acid

ATPase on plasmalemma hydrolyze ATP

malic acid dissociates and prpduce H+

Water potential declines

H+ is pumped out of guard cells andK+ is pumped into of guard cells

Guard cells turgor pressure increase

Stomatas opens

K+ go in or out of the stomatal guard

cells

Inorganic ion uptake theory

3. Water transportation in plant

植物体内的水分运输

（ 1 ） pathways that water go through into plant cells.

a . A single water molecule go through the space between lipid bilayer and go into plant cell.

b . Water affluence go through the water channels commposed by aquaporins on plasma membrane and go into plant cell.

aquaporin ： Aquaporins are membrane water channels that play critical roles in controlling the water contents of cells.

（一）水分进入细胞的途径

1 、单个水分子通过膜脂双分子层的间隙进入细胞

2 、水集流通过质膜上水孔蛋白组成的水通道进入细胞

水孔蛋白：是一类具有选择性地、高效转运水分的膜通道蛋白。

Transportation of water in plant

植物水分的运输

soil water root hair root cortex pericycle

root vessel stem vessel petiole vessel

vein vessel mesophyll cell intercellular space

substomatic cavity stoma atmosphere

Pathways with which water transport in plant body

水分在植物体内的运输途径

1 ） symplastic transport ( 共质体运输 ) 所有细胞的原生质

体通过胞间连丝联系形成从原生质体到原生质体的连续体系。

“活”的部分；阻力较大，短距离运输。

2 ） apoplastic transport ( 质外体运输 ) 指植物体内所有

的细胞壁、细胞间隙等没有原生质的部分所组成的一个连续整

体。该途径速度比共质体运输快，但慢于管分子通道运输。

Graphical Illustration of symplastic and apoplastic transport

3 ） vessel system transport ( 导管或管胞系统的运输 )

由导管或管胞等死细胞组成的中空长管道，水分在其中

运输。管道中的水依靠水的内聚力可以形成一条连贯的水柱。

运输的动力来自上部的蒸腾拉力和下部的根压，上拉下推使

水分上升。

迅捷的长距离运输方式

2. Driving force for water acsend along vessel

水分沿导管或管胞上升的动力

水分上升的动力：根压和蒸腾拉力

水分上升的原因：内聚学说（ cohesion theory ），蒸腾—内聚力—张力学说

（ transpiration-cohesion-tension theory ）

争论较多； 目前仍是唯一被认为足以给植物体内水分上

运提供一个合理解释的学说。

Plants’ roots,stem and leaves be regarded as a continuous watercolumn

(mesophyll cells-root cells), laminas absorb water from vessel because of

the transpirational dehydration. The tracheal watercolumn receives a

tractive power and also bounds by the force of gravity so that generates

a tension. Because of that water cohension is much bigger than tension o

f watercolumn, so can maintain the continuity of water so that it can acs

end continuously.

Transpiration-cohesion-tension theory

1） tension of watercolumn (- 0.5 ~ - 3MPa)2） biggish cohesion between water molecule (+20 ~ + 30MPa ), cohension >> tension3 ） water have great adhesion to vessel wall.

植物的根茎叶导管内的溶液可看作一个连续的水柱（叶肉细胞 —— 根细胞），叶片因蒸腾失水而向导管或管胞吸水，导管或管胞的水柱受到蒸腾的拉力向上牵引时，也必然受到重力的牵引，上拉下拽使水柱产生张力，由于水分子内聚力大于水柱张力，保证水柱的连续性而使水分子不断上升。

蒸腾－内聚力－张力学说。

1 ）水柱有张力（ - 0.5 ~ - 3MPa ）

2 ）水分子间较大的内聚力（ +20 ~ + 30MPa ），内聚力 > ＞张力

3 ）水分子对导管壁有很强的附着力

Water transportation

for plant

Transpiration indexs

Transpiration rate ： certain time, area of unit leaf ,quantity of water dissipate. g-1m2 h

Transpiration ratio ： the quantity of dry matter maked by 1kg of water dissipate , g-1kg

Transpiration coefficient ： consumption of water that forms 1g dry matter, g-1 g

Section Ⅲ mineral nutrition

mineral nutrition ： the study of how plants obtain, transport

and assimilate mineral nutrients is called min

eral nutrition.

Mineral nutrients

Cu 、 Fe 、 B 、 Zn 、 Mo 、 Mn 、

Na 、 Cl ……

elemental composition

macroelement 10 -2 microelement 10 -3-- -5

C 、 H 、 O 、 Mg 、 Ca 、 K 、

S 、 P 、 N

收多收少在于肥庄稼一

枝花，全靠肥当家

mineral nutrients in plant

according to the physiological functions of mineral elements

constituents ： participate in the composing of Plant cells physical structure

regulatory components ： regulate life activities of plant cells.

according to the requirement for plant essential elements

macroelement ： Its content is more than 0.01% （ 10-2 % ） of dry matter in plant.

microelement: Amounting 10-5- -3 % of dry matt

er in plant ，

Root system uptakes mineral elements from soil inorganic salt,

In natural condition ， all the soil inorganic salt is airslaked from mineral elements.

Essential elements for plant growth

Essential elements:

C 、 H 、 O 、 S 、 P 、 N 、 K 、 Ca 、 Mg 、 Fe

、 Cl 、 Mn 、 Zn 、 Cu 、 B 、 Mo 、 Ni

An essential element is defined as one whose absence pre

vents a plant from completing its life cycle or one that ha

s a clear physiological role.

These elements can synthesize compounds which plant n

eeds or participate in plant metablism.

main function for some common minerals in plant cells

The fuction and symptoms of specific nutritional deficiencies

作物营养元素缺乏症状检索表

病 症 缺乏元素

A．病症在老叶 （老叶先发病）

B．病症常遍及整株，基部叶片干焦

C．植株浅绿，基部叶片发黄，干燥时呈褐色，茎短而细 ……………………………………氮

C．植株深绿，常呈红或紫色，基部叶片发黄，干燥时暗绿，茎短而细 ……………………磷

B．病症常限于局部，基部叶片不干焦但杂色或缺绿，叶缘杯状卷起或皱缩

C．叶杂色或缺绿，有时呈红色，有坏死斑点，茎细 …………………………………………镁

C．叶杂色或缺绿，有坏死的大斑点或小斑点

D．坏死斑点小，常在叶脉间，叶缘最显著，茎细 …………………………………………钾

D．坏死斑点大，普遍出现在叶脉间，最后出现于叶脉，叶厚，茎的节间短 ……………锌

A．病症在嫩叶（幼叶先发病）

B．顶芽死亡，嫩叶变形和坏死

C．嫩叶初呈钩状，后从叶尖和叶缘向内死亡 …………………………………………………钙

C．嫩叶基部浅绿色，从叶基起枯死，叶卷曲 …………………………………………………硼

B．顶芽存活但缺绿或萎蔫

C．嫩叶萎蔫，常有斑点或缺绿发黄，茎尖柔弱 ………………………………………………铜

C．嫩叶不萎蔫，具有缺绿症

D．坏死斑点小且散布全叶、叶脉仍绿 …………………………………………………… 锰

D．无坏死斑点

E．叶脉仍绿 ……………………………………………………………………………… 铁

E．叶脉仍绿 ……………………………………………………………………………… 硫

When any of the essential elements are deficient in the plant, characteristic deficiency symptoms appear.

3. Absorption for mineral elements in plants

(1). Passive absorption ： Absorb mineral elements by physical process such as diff

usion action, one kind of energy-free metabolism. Substa

nce moving from a region of high concentration to a regi

on of lower concentration by simple diffusion. The main

reason for passive absorption is the intracellular or extra

cellular concentration difference.

(2). Active absorption ： Active absorption is the expenditure of energy by a cell that results in molecules or ions entering or leaving the cell against a diffusion gradient.

Mechanism of active absorption ： ion carrier theory ion pump theory ion channel theory

Root system also can absorb some mineral elements by ion exchange process. For example, CO2 produced by root breath dissolves into the soil solution and becomes H+ and HCO3

－ , H+ exchange with K+ adsorbed on the surface of soil colloidal particles, so that K+ goes into the soil solution and can be absorbed. it also can absorb mineral elements by contact exchange process, namely, H ＋ on root cells directly exchange with K ＋ on soil particles.

3 、 absorption features ：1 ） Associated with moisture absorption and also relatively indep

endent ;

2 ） The selective absorption for ion

3 ） toxic action of single salt

plants, cultured in a single salt solution despite an essential low-c

oncentration salt, absorb more than a certain amount of mineral e

lement, and then will be poisoned and die. This principle is known

as toxic action of single salt.

4 ） ion antagonism

if adding some other metal-ion salt into a single salt solution, it wi

ll reduct or eliminate the toxic action of single salt. This kinds of i

nteractions between ions is called rivalry or antagonism.

4.Transportation of mineral elements in plant cells

The same to water transportation: symplastic transport, apoplastic transport and vessel system transportDifferent in trace ： water is transported to plant leaves, while mineral elements are transported to a growth center of a time.

Transportion of minerals in plant cell

1. endoderm 2. casparian strip 3. pericycle 4. root hair 5. epidermis 6. cortex 7. xylem 8. phloem