01chemistry

8/13/2019 01chemistry

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Chapter 1 Water Relationship in Plant

P201-240 (W.G. Hopkins &N.P.A. Hner)

Water absorption from environment , transportationand distribution in plant body, and water loss toatmosphere etcwater relationship

Abundant or without harvest dependant onwater

Section1 Role of water in plant life

1.1.Structure and physi-chemical characters ofwater


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O H

H

104.9o

H

HH

O

H

HO H

H

hydrogen bond

A.Water is a polar molecule with hydrogen

bond among water molecules

- +

+


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B. High specific heat and latent heat ofevaporation (heat of vaporization,) C. Great surface tension() and cohesion(

Figure 1-1 Water mounts

along with grass wall by

cohesion


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D. High dielectric constant()and an extensive solvent ()Table 10.2 Dielectric constants for some common solventsat 25 C

1.9Hexane

2.3Benzene

24.3Ethanol

33.6Methanol78.4Water


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D. High dielectric constant()and an extensive solvent ()

colloidal

particle

colloidal

particle

+

+

++

+ ++

+

++

++

+

+

+++

+

Figure 1-2 Hydrophilic colloidal particle

and its hydration shell


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1.2 Water content and status in plant 1.2.1 Water content 1.2.1 Water content 1.Plant types Water plants (hydrophytes) >90%

Land plants 40-90%

Xerophilous plant () ~ 6%

Herbs >trees


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1.2 Water content and status in plant 1.2.1 Water content

1.Plant typesWater plants (hydrophytes) >90%,Land plants 40-90%,Xerophilous plant ~ 6%,Herbs >trees

2.Growth environments shade plants>sun plants


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1.2 Water content and status in plant1.2.1 Water content

3.Organs Stem tenders and roottips>90%, function leaves 70-90%,tree stem 40-50% dormancy bud40%, wind-dried seeds 8-14%

The higher life activity, the higher water

content.


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1.2.2 Status in plant.

Free water and bound water

free waterIt does not tightly bind tocomponents of cell and it moves freely in

the plant.

Special characters: participate in

metabolism, take as solvent and easily

freeze


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1.2.2 Status in plant.

Free water and bound water

free water bound waterIt tightly bind to

components of cell and does not move in

free in the plant.

Special characters: not to participate in

metabolism, not to take as solvent and notto freeze easily.


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In plant metabolic activity, growthsituation and resistance are all dependent

on the ratio of free water to bound water.

The higher ratio, the higher metabolism and

the faster growth, but lower resistance because

protoplasm is of sol.

The lower ratio, the lower metabolism and the

slower growth, but higher resistance becauseprotoplasm is of gel.


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1.3 Role of water in plant life

(1)Component of protoplasm

Protoplasm in plant contains 70-90% water. (2)Substrate for plant metabolism

Photosynthesis, respiration and biosynthesis

or degradation of organic substance.


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1.3 Role of water in plant life

(1)Component of protoplasm

(2)Substrate for plant metabolism

(3)Solvents for plant absorption and

transportation

(4)Keeping plant in shape (extension)

(5) Balance plant temperature


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Section2 Water absorption by plant cell

3 ways: Osmosis absorption(mainly)

imbibition absorption; metabolism absorption.


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2.1 Osmotic() absorption of water

by plant cell

2.1.1 Free energy, chemical potential and waterpotential

bound energy and free energy

free energy can work and participate in chemicalreaction.

Chemical potential: the free energy per mole ofthat substance. Therefore, water chemical potentialis the free energy per mole of water, which iscalled water potential in plant physiology.


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Water potentialWater potential isdefined as the difference in free energy per

unit volume, between matrically -bound,

pressurized, or osmotically- constrainedwater and pure water.

w=(w / Vw) - 0wVw) =(w-0w)Vw =wVw

w reflects the capacity for chemicalreaction and movement in plant system.


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Suppose:w

0 of pure water is zero.

w of solution water is minus.

The higher concentration, the lower (minus)

w.

w Unit: MPa=106Pa=10bar Sea water: -2.5M Pa 1M NaCl:4.46MPaPlant cells:-0.1~ -1.5MPa


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2.1.2 Osmosis and osmotic potential

Diffusion():matter transfers fromhigher concentrations (energy) to lowerconcentrations (energy)

Figure 1-3 Solute diffuses


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Osmosis () is a diffusion inwhich solvent molecules pass through

semipermeable membrane ().

Figure 1-4 See movie for osmosis

semipermeable

memb

rane


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Semipermeable membranevesica, seed coat,dialysis bag etc.

Osmotic potential ( Solute potentials )

The decreased part of water potential caused by

existence of the solute in the solution

s(Mpa)= -0.0083iCT iosmotic coefficientNaCl: i=1.80CaCl2: i=2.60,

Sucrose: i=1.

Csolute concentration

Tabsolute temperature


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2.1.3 Plant cell is an osmotic system Cell wall ( consists of cellulose,pectin and

semi-cellulose)A permeable membrane

Protoplastic layer (Plasmic membrane and

tonoplast)A semipermeable(selective)

membrane

Plasmolysis () and Deplasmolysis

(


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In higher

concentration of

solution

Plasmolysis

Deplasmolysis

Return to the lowerconcentration of

solution

Figure 1-5 Plasmolysis and Deplasmolysis

The protoplast

shrinks awayfrom cell wall.


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Significance for plasmolysis and deplasmolysis Protoplastic layer has selective permeability.


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Protoplastic layer has selective permeability.Judge cell alive or dead cell .


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Protoplastic layer has selective permeability.Judge alive or dead cell from this.Determine cell water potential, and

resistance of crop to drought.

Determine the entrance speed ofsubstance into cell, easily or difficulty.


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2.1.4 Water potential elements of theplant cell

w=s+p+m

ssolute potentialDepending onsum of solute particles (molecules or ions)

Normal plant leaf: s=-1 -2 MPa xerophilous plant leaf:s reaches to -10MPa

s has diurnal and seasonal changes


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p pressure potential The increased part of water

potential caused by turgor

pressure. Normal conditions: Positive

value (p>0) Herbs (warm weather+0.3

+0.5MPa in the afternoon+1.5MPa at night

Special conditions: zero or

minus Incipient plasmolysis=0, Over transpiration


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m

matric potential The decreased part of water potential results

from cell components absorbing water.

Minus

Wind-dried seed, m -100MPa Obvious m in the cell before formation of

vacuole . Cell with large vacuole >-0.01MPa could be

neglected

So, w=s+p in general cell .


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2.5

2

1.5

1

0.5

0

0.5

1

1.5

0.9 1 1.1 1.2 1.3 1.4 1.5

w(M

pa

)

Cell volume(times)incipient

plasmolysis

3fully turgid cell

w=0

p= -

s

Exceptions:

1intensivetranspiration

p


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2.1.5 Water movement between cells inplantdependent on w

s = -1.2MPa

p = 1.0MPas = -1.0MPa

p = 0.9MPa

s = -0.8MPa

p = 0.4MPa

A B C


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s = -1.2MPa

p = 1.0MPa

w =-0.2MPa

s = -1.0MPa

p = 0.9MPa

w =-0.1MPa

s = -0.8MPa

p = 0.4MPa

w =-0.4MPa

A B C

A CFigure 1-7 Water moves depending on water potential


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Isotonic solution,

Hypertonic solution,

Hypotonic solution

Fig 1 8 water potentialin soilplantaircontinuous system

Wate

rflowdirection

w-air

w-leaf

w-xylem

w-root

w-soil


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2.2 Imbibing absorption of water of plantcell

Imbibition () is a phenomena inwhich hydrophilic colloids enlarge withwater absorption.

Only depend on components (hydrophilic

group)protein>starch>cellulose> >lipidand fat

Soybean has extreme imbibition.


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Imbibition is a power of water absorption forvacuole-unformed cell , such as wind-dried

seed and meristematic cell.

Imbibition is droved by ms=0p=0w=m


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2.3 Metabolic absorption of water by plant cell

The plant cell uses the energy produced in

respiration and drives water absorption across

plasmatic membraneMetabolic absorption

of water

Proofs:

Respiratory inhibitors (dinitrophenol,DNP and

azide, N3-) block water absorption and respiratory

promoters (sugar) enhance water absorption.


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2.4 Water channel proteins or aquaporins

Aquaporins in all living cell are a serious

proteins which located in plasmaticmembrane or tonoplast, and play animportant role in water transmembranetransport because they have less resistance towater and speed up water transport acrossthe membrane.

About 80% of water entrance is controlled byaquaporins.


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Fig 1-9 Aquaporins facilitate the diffusion ofwater and small neutral solutes across plant

cell membranes.

The putative structure or an aquaporin monomer

with six tilted membrane-spanning domains

PN P A

NPAP

NA

H2

O

H2O Small neutral solutes


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Aquaporins have other possible functions Reproductive grow , cell elongation,

guard cell behaviors, cell turgor and

volume regulation, transpiration, watercycling in xylem and phloem, nutrition

absorption and response to drought and

salty.


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Section 3 Absorption of water by plant root

3.1 Absorption

region

Main part for

absorption ofwaterthe

region of root

hair

Lateral root

Root

hair

Root

cap

Figure 1-10 Model of root tip


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1.Greatnumbers of

root hair

cells, largeabsorption

area


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2.Thin cell

wallbetterwater

conductivity 3.Well

developed

conduct tissues.

Figure 1-12 Anatomy of root tip


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Why should tree rootbe maintained with a

bulk of original soilwhen transplanted?


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3.2 Water absorption by rootactiveand passive

3.2.1 Active uptake of water

A phenomenon in which water

absorption is taken by the physiological

activity of root.


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Root pressure () is a power which pusheswater to mount along vessel, depending onphysiological activity of root.

0.1-0.2MPa .

Much or less depending on stronger or weakerphysiological activities of the root (plant).

Bleeding ()a phenomenonthat the sap flows out from the wounded

(cut) partbleeding sap (seemovie).


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Figure 1-13 Guttation


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Guttation (

)when soil hasenough water and atmosphere is warm

and higher relative humidity (RH), often

in the early morning, unwounded leafcan secret sap from the tip or margin

(water pore) of leaf.

Guttation often appears in lotus, strawberry

and gramineous crop. An index for healthy seedlings.

Wh d t ?


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Casparian

band

Why does root pressure occur?


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Apoplast: A continuous system is consist of cell

wall, cell space (interplace) and vessel of xylem,except protoplast, considered as a non-life partin the past.

Less resistance and higher speed of transport forwater.

Symplast: A continuous system is consist ofprotoplast, plasmodesma and plasmicmembrane, considered as a life part exceptapoplast.

Water enters symplast by osmosis and than wateris transported across cell by cell.

3 2 2 Passive uptake of water


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3.2.2 Passive uptake of water

Passive uptake

is driven bytranspiration

of leaf

Po er Transpiration p ll ( )


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Power-- Transpiration pull (). Transpiration pulla power driving water

upward along xylem vessel is decided by agradient of water potentials due to transpiration.

Independent of root metabolism

Main means for water absorption.

Especially under the intensive transpiration. But plant can mainly absorb water by active

absorption upon low transpiration or without

transpiration, such as in the early spring and whenthe leaves unexpand.


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3.3 Factors affecting water absorption byroot

Inner factorsw , development degree,water conductivity and respiration of roots

Outer factorsair factors transpirationwater absorption (indirectly) . Soil factors directly influence water

absorption of root.


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(1) Soil available water (is referredas the water can directly be taken up and utilized

by plants, whose water content is higher than

wilting coefficient in the soil.

wilting coefficient() is a soil watercontent (%) under which plant will occur wilting

permanently .

Under the condition of water deficiency, leaves and

tender stems will loss their turgor, called wilting.


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Figure 1-16 Plant wilting


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Temporary wilting () The wilting iscaused by loss of equilibrium between waterabsorption and evaporation (main transpiration).Transpiration is larger than absorption.

Normal status can be recovered by shading, or in theevening upon decreasing in transpiration, but not bywatering.

Permanent wilting ()The wilting iscaused by no soil available water, plant can notabsorb water from the soil.

If the permanent wilting just happened, normalstatus can be recovered by watering or waterspraying, but not by decreasing in transpiration.


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(2) Soil O2 CO2N2 treatmentabsorption

because O2 , respiration ,activeabsorption, anaerobic respiration,Ethanol accumulation, root toxication.


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(3) Soil temperature

Low temperature: water and

plasma viscosity(), water

conductance

respirationenergy not enoughroot growth and root hair

Too high Troot corkification

easily

water conductance

Uptakerateofwater

Temperature

Low HighOptimum


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(4) Soil solute concentrationw in root < w in soil, usually soil >-0.1MPa.

Why should we not apply a large number

of fertilizer to plant in one time?

S ti 4 T i ti


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Section 4 Transpiration

More than 95% of water loss in air, and

only1-5% for plant metabolism.

(1)liquid form--guttation (2)gas form--transpiration

Transpiration ()is a process ofloss water from plant in a form of watervapor.


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4.1 Organs for transpiration Lenticular transpiration () about

0.1%

Most of transpiration passes throughout

leaf of plantcalled Leaf transpiration.


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4.1 Organs for transpiration Lenticular transpiration

*Leaf transpiration :

Cuticular transpiration (), 5-10 Stomatal transpiration (),90-95%

4 2 S l i i


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4.2 Stomatal transpiration

4.2.1 Size, number and distribution of stomata

Stomata ()pore for gas exchange (main

CO2, O2 , Water vapor)


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Figure 1-14 Stomata in the lower epidermis of potato leaf


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Table1-2 The number, size and distribution of stomata in plantsPlants Number/ epiderm (mm

2) Size() Single area Total area

The upper The lower Lengthwidth (2) /leaf area (%)

Wheat 33 14 387 209 0.52

Maize 52 68 195 75 0.82

Oat 25 23 388 239 0.98

Sun flower 58 156 228 136 3.13

Tomato 12 130 136 61 0.85

Bean 40 281 73 17 0.84Apple 0 400 1412 132 5.28

Lotus 46 0 - - -

U id i


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Upper epidermis typehydrophyteslotus Lower epidermis type most trees:apple and

peach trees.

Both epidermis type most herbs includingcrops. But stomata are in the lower epidermis

more than in the upper epidermis.

In grain plants, those distribution is nearly equal in

the lower epidermis to in the upper epidermis.

4 2 2 Stomatal diffusion Law of micro


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4.2.2 Stomatal diffusionLaw of micro-

pore diffusionperimeter diffusion

Table 1-3 The relationship between rate of water

diffusion and pore area or perimeter

D of pore Relative Relative Water loss Relative

(mm) area perimeter (g) water loss

2.64 1.00 1.00 2.655 1.00

0.95 0.13 0.36 0.928 0.35

0.35 0.01 0.13 0.364 0.14

L f i diff i diff i t f


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Law of micro-pore diffusion: diffusion rate ofwater vapor throughout poly micropore is notproportional to the area, but is proportional to theperimeter.

In the margin less chance of collision.Diffusion rate is larger in the margin than inthe middle.

Diffusion by

macropore

Diffusion by poly micropore

4 2 3 Mechanism for stomatal opening and


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4.2.3 Mechanism for stomatal opening and

closing (p90-98)

Opening in daytime and closure at night

resulted from the swelling by waterabsorption or shrinking by water loss in

guard cells.

Stomatal complex Guard cell , subsidiary cell and

substomatal space.

Figure 1-15 Stomatal complex structure


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Guard cell

subsidiary cell

Dumbbell shape

Guard cell


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Orientation of microfibrils allows the expansion of the

cell only in the direction shown by the dashed arrows.

Subsidiary cellStomatal complex in dicot

Stomatal complex

in monocot

Figure 1-16 The stomatal complex in dicot and monocot

(1) Starch-sugar conversion theory


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(1) Starch sugar conversion theory Starch phosphorylase (SPLase) plays

an important role in stomata openingand closing.

pH>5.0 hydrolysis activity ,pH


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(1) Starch sugar conversion theory

Stomata closure

darkness

Respiration in GC

Produce CO2cell pHSPLase synthesis activity

G-1-P to starch

Water potential Loss of water and turgor

Stomata opening

Light

Photosynthesis in guard cell(GC)

Consume CO2Cell pHSPLase hydrolysis activity

Starch becomes G-1-P Water potential

GC absorbs water and turgor

(2) Potassium ion pump or inorganic ion


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( ) p p g

uptake theory

Guard cell

Open Close

OuterSubsidiary cell

Inner

Subsidiary

cell

Figure 1-17 the change in K+ and pH of guard cell and

subsidiary cell during stomata opening and closing

0.

16

0.

29

0.

2

0.

10

pH5.78

pH5

.56

0.1

0.4

5

pH5

.60

pH5

.19

(2) Potassium ion pump or inorganic ion


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uptake theory

Stomatal opening

LightdarkGuard cell(GC) photosynthesisrespiration

ATP and malate ATPase hydrolysis ATP, malate dissociates H+

H+ pump out of GCK+pump into GCWater potential

GC absorbs water and turgor

outer inner

ATPase

ATPH+

H+

K+K+

K+K+

Figure 1-18


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http:/Bio.fsu.edu/

~outlaw/assorted/

k-salts.html

Stomata opensand closes

4.2.4 Factors affecting stomatal opening


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. . Factors affecting stomatal opening

and closure

(1) light: form sugar and malate, acumulate

K+

and Cl-

About 2.5% of full sun light

Sensitive to blue light, UV-A receptor (blue

light receptor)

Lot of gene relevant to stamatal behavior

iveNPQ1 PLA2

linolenic acid/

PP1/PP2AOA sensitive Protein

14-3-3 protein

fusicoccin


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Light

H+ pump

K+inchannel S

tomatal

opening

Positi

Negative

(blue light)linolenic acid/

arachidonic acid

OA sensitive

Kinase

ABA

abi1-1

abi2-1

ozone Ca2+

InsP3

InsP6

PP2B Actin filament

Protein kinase/CDPK

Fig 1 A simplified working model for proposed function ofpositive and negative regulators in light-induced stomatal

opening. For simplicity, parallel signaling branches are not

included here.

(2) CO2:


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( ) 2 Low CO2 ,stomatal openinghigh CO2 ,

stomatal closure because of acidificationand K+ leakage from guard cell.

(3) Relative humidity in atmosphere: higherRH, larger opening. Low RH, loss of water

of Guard cell. (4) temperature.

In arrange of T, T rises and opening

increases. Optimum 30 the openingbecome smaller at >35

(5) leaf water and potassium contents


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The higher water and enough potassium,

the opening larger. Too much water

condition blocks stomatal opening (6) plant hormones

ABA---close, ABA promotes Ca2+ increase

in cytosolindirectly makes K+Cl- flow

out of GC and inhabits entrance of K+into

GC. IAA CTK result in stomatal opening

ABACa2+permeable

K+in channel


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Ca2+

Ca2+

channel

Vacuole

Dep

olariz

e

K+

K+out channel

A-

S-type

anion channelR-type

anion channel

pH

Ca2+H+

ATP

ADP+Pi

Fig 2 A guard cell model, illustrating the proposed functions

of ion channels in ABA signaling and stomatal closing. Theright of the stomatal shows ion channels and regulators that mediate ABA-induced stomatal closing. The left cell shows the parallel effects of ABA-

induced [Ca2+]cyt increases that inhibit stomatal opening mechanisms.

4.3 Internal and environmental conditions


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affecting transpiration

Boundarylayer

Substomatal space

T

eleaf-eair

rleaf+rair

e=vapor pressure

r=resistance

4.3.1 Effect of internal factors on transpiration


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Stomatal density (number/leaf cm2) Opening degree

Leaf waterCO2 and ionspotassiumcontents

ABA The areas of leaves or leaf cells;

The transplanted plants are often cut the

branches and leaves!

4.3.2 Effect of environmental factors on


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transpiration (1) light lighttranspiration

openingresistanceTleaf

and Tair

transpiration The difference ofvapor pressure between in the leaf and air

(2) Atmosphere relative humidityRH

transpiration RH too lowstomatal

closure transpiration

(3) Air temperature In arrange T


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transpiration Too low or high transpiration (4) Wind Breeze transpiration the

thickness of boundary layer (5) Air CO2 transpiration (6) Other factors which affect water absorption

4.3.3 Diurnal change of transpiration


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020406080

100120

4 8 12 16 20Time of day

Relative

transpiration)

Clean day

Dry and hot day

4.4 Role and index of transpiration


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4.4.1 Role

(1) It decreases in leaf temperature;

(2)It is a power for water absorption andtransportation.

(3) It enhances the transfer and distribution

of mineral nutrition and other solutes in

plant body.

4.4.2 Index


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(1) Transpiration rate ()Waterloss of plant through transpiration per unit

leaf area and per unit time (g/m2

s) .

daytime1.5-7.5 g/m2s night


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ratio() Plant producesquantity (g) of dry mater when it consumes 1kg ofwater by transpiration.

Wild types 1-8g/kg crops 2-10g/kg

Water utilization efficiencyWUE,

Special definition Photosynthetic rate (CO2mol/m

2s )

Transpiration rate (mmol H2O/m2s )

Intensive definition= Transpiration efficiency

WUE=

(3) Transpiration coefficient or water

i t (


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requirement ( Water requirement is a reciprocal of

transpiration efficiency, means that plant

consumes water quantity (g) for making

1g of dry matter.

Wild types:125-1000 g crops:100-500 g .

Section5 Water transport in plant

5 1 P th f t t t


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5.1 Pathway of water transport


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5.1.1 Short distance transport


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Transport form root

hairs to root vessels.

Largest resistance is

in endodermis.

Casprian band blockswater transport throughapoplast.

Transport form terminal vessels(tracheids) of leaf

to substomatal space


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to substomatal space

Leaf tracheids

Air

stomata

5.1.1 Long distance

transport


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transport Transport in rootvessels (or tracheids)

to leaf vessels (ortracheids)

Vessels in angiosperm

and tracheids ingymnosperm.

Less resistance to

water transport

5.2 Power of water

transport

Root pressure in


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Root pressure inbottom,

Transpiration pullin top

Transpiration-cohesion-tension theory() water can be


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)water can betransported in a continuous water

column because water cohesion is larger

than its tension.

5.3 Rate of water transport

S l 1 /h


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Symplast1mm/h.

Xylem3-45m/h.

Angiosperm:1-40m/h

Gymnosperm


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physiology

Maximum efficiency with the least water!

6.1 Law of plant water requirement 6.1.1 Plant typesTable 1-5 Water requirements for different crops

Crops Maize Sorghum Barley Rice Bean Potato Cotton

Water requirements 370 322 520 680 700 640 570

6.1.2 Growth stages


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SeedlingTillering or

branching

Flowering and

setting Ripening

Relativew

aterrequirement

Growth stages

Critical period of water(): a

period during which plant is most sensitive


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period during which plant is most sensitiveto water deficiency and is most easily

injured by this, but the water requirement is

not always largest at that period. a period from pollen mother cell meiosis to

pollen tetrad(4).

Two Critical periods of water for grain crops:

Stem elongation from pollen mother cellmeiosis to pollen tetrad and filling stage.

6.2 Index for effective irrigation

6 2 1 Morphological index


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6.2.1 Morphological index

(1)The tender stems and leaves wilt.

(2)Stem and leaf appear in darkness orreddish.

(3) Growth delay.

6.2.2 Physiological index

(1)Leaf relative water contents()


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(1)Leaf relative water contents() A percentage of the actual water content to the

water content of the leaf with water-saturated.

Leaf relative

water contents (%)=

FW-DW

FW

SFW-DWSFW

100%

FW=fresh weight of leaf, DW= dry weight of leaf,

SFW=the water content of leaf with water-saturated

if Leaf relative water contents


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-0.4

-0.8

-1.2

-1.6

normal

Water

deficient

Recovered in the eveningnot necessary to irrigateNot recovered in the dawn, necessary to irrigate

Waterpotential(M

Pa)

6.2.3 Irrigation methods

(1)ground irrigation.


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(1)ground irrigation.

Alternative irrigation

(2)sprinkling irrigation.

(3)dropping irrigation.

1. Cloze

(1)When the cell is bathed by a solution, water will enter


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the cell as it moves down the water potential gradient; When the cell isbathed by a solution, which has more negative osmoticpotential than the cell, the protoplast will shrink away from the cell

wall. It is known as . (2) Transpiration is defined as , by

which water loss passes mainly through the in theepidermis of the leaves.

2.Question: (1) What are water potential, osmotic potential and pressure potential?

Describe the relations among them.

(2) what is driving force for water movement in the xylem?

(3) Why do we not irrigate plant with cold water at noon in the sunnysummer day?

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