植物生理學(xué)：第三節(jié) 水分(虧缺)脅迫及植物的抗旱性

第三節(jié)水分(虧缺)脅迫

(water

deficit

stress)及植物的抗旱性包括干旱(drought)脅迫（由自然環(huán)境缺水引起）和脫水(desiccation)脅迫（實(shí)驗(yàn)室人為脫水引

起）；為鹽(salt)脅迫和滲透(osmotic)脅迫的組成部分。旱生植物：生長(zhǎng)于極端干旱地區(qū)，如沙漠；形態(tài)、功能上特殊機(jī)制，能抗極度脫水；復(fù)水后“起死回生”中生植物：耐受一定范圍內(nèi)的脫水，產(chǎn)生相應(yīng)的生理反應(yīng)；大部分高等植物Craterostigma

plantagineum

plants.

(A)

Fullyturgid

plant.

(B)Desiccated

plant

(unwatered

for7d).

(C)

Plant

rehydrated

for

6h.中生植物的生理變化與耐旱性：地上部生長(zhǎng)延緩，乃至部分葉片脫落。降低失水；根系縱向生長(zhǎng)加快，增加吸水；根/冠(R/T) 增大氣孔關(guān)閉，光合作用下降A(chǔ)BA上升滲透調(diào)節(jié)物質(zhì)大量合成水分脅迫誘導(dǎo)的基因表達(dá)ABA在植物中起傳遞旱情的信號(hào)：

Accumulation

of

ABA

in

maize

roots

and

in

xylemsap

as

a

result

of

soil

drying.

Effect

of

manipulating

ABA

concentration

in

xylemsap

on

stomatal

conductance

of

leaves

(abaxialepidermis)

in

maize.透調(diào)節(jié)物質(zhì)(osmolyte):高度水溶性、不干預(yù)細(xì)胞代謝的有機(jī)化合物。The

chemical

structures

of

some

important

cellular

compatible

osmolytes.脯氨酸

Proline甜菜堿

Betaine脯氨酸甜菜堿

Proline

betaine甘露醇

Mannitol透調(diào)節(jié)作用(osmotic

adjustment)：Osmotic

adjustment

occurs

when

the

concentration

of

solutes

within

a

plant

cellincrease

to

maintain

a

positive

turgor

pressure

within

the

cell.水分脅迫響應(yīng)基因亦受干旱、ABA和低溫誘導(dǎo)Accumulation

of

RAB18

&

LT178

mRNA

in

Arabidopsis

thaliana.通過(guò)抗旱鍛煉能提高植物的抗旱性抗性鍛煉：植物經(jīng)過(guò)一段時(shí)間的自然或人工的非致死脅迫后，往往增強(qiáng)了對(duì)該脅迫的抗性。“蹲苗”：適度干旱措施第四節(jié)澇害(flooding)與植物的抗?jié)承訮lants

vary

in

ability

to

tolerate

flooding

Wetlandplants

Flood-tolerant

plants

Flood-sensitive

plantsSweet

flagArabidopsis

thalianaSoybeanRice

grassBarnyard

grassTomatoBarnyard

grassOatPeaCoral

treePotatoGolden

dockWheatRiceCornWild

rice

A

flooded

maize

field.Flooding

in

the

USMidwest

in

1993

resultedin

an

estimated

33%reduction

in

yieldcompared

with

1992.Survival

strategies

of

a

freshwater

weed.Hydrilla

verticillata

(L.f.)

Royle,

a

monocotyledous

native

of

Asia,

is

an

invasivesubmerged

weed

in

freshwater

ecosystems

in

the

southern

US.Hydrilla

develops

as

a

dense

mat

of

stems

and

leaves

near

the

surface

of

the

water.These

plants

now

threaten

waterways

in

Florida

and

other

Southeastern

states.Wetland

plants

posses

diverse

anatomical,

morphological

and

physiologicalfeatures

that

permit

survival

in

aquatic

environments

or

waterlogged

soilsAerenchyma:

continuous,

columnar

intracellularspaces

formed

in

root

cortical

tissuesAerenchyma

development

in

root

cortex

of

maize

after

oxygen

deprivation.(A)

under

aerobic

conditions,

(B)

under

72h

of

hypoxiaLenticels:

openings

in

the

periderm

that

allow

gasexchange

Adventitious

roots

and

prominent

lenticels

on

the

stem

of

young

ashafter

flooding.

The

black

arrow

indicates

the

water

depth

duringflooding.Pneumatophores:

shallow

roots

that

grow

withnegative

geotrophy

out

of

the

aquatic

environment.Pneumatophores

of

mangrove

develop

from

rootssubmerged

in

estuarine

mudInternodal

stem

elongation:

enables

stems

and

leavesto

be

established

above

the

aquatic

environment.

(A)Diagram

illustrating

growth

response

of

seedlings

deepwater

rice

toflooding.

Submerge

promotes

rapid

internodal

elongation

anddevelopment

of

adventitious

roots.

Once

the

flood

waters

recede,

theadventitious

roots

grow

into

the

soil

and

aerial

portions

of

the

plantgrow

upward.

(B)

Photographs

comparing

internode

elongation

in

aerobic

(left)

andsubmerged

(right)

plants.

Arrowsindicatepositions

of

nodes.During

short-term

acclimation

to

anoxic

conditions,plants

generate

ATP

through

glycolysis

andfermentationMajor

fermentation

productsof

carbohydrate

metabolismin

flooded

rootsImpact

of

oxygen

deprivation

onrespiratory

metabolismOxygen

status

Effect

on

metabolismNormoxic

(aerobic)Aerobic

respiration

proceeds

normally.

Almost

all

ATPproduction

results

from

oxidative

phosphorylation.HypoxicThe

partial

pressure

of

O2

limits

ATP

production

by

oxi-dative

phosphorylation.

Glycolysis

accounts

for

a

largerpercentage

of

ATP

yield

than

under

normoxic

condition.Metabolic

and

developmental

changes

are

stimulatedthat

result

in

adaptation

to

a

low-oxygen

environment.Anoxic

(anaerobic)ATP

is

produced

by

way

of

glycolysis.

Cells

exhibit

lowATP

contents,

diminished

protein

synthesis,

andimpaired

division

and

elongation.

If

anoxic

conditionspersist,

many

plant

cells

die.Effects

of

hypoxic

pretreatment

and

acclimation

onsurvival

of

anoxia:

avoidance

of

cytoplasmic

acidosisby

lactate

efflux.Flooding

typically

results

in

hypoxia,

followed

by

anoxia.

Exposureof

maize

seedlings

to

hypoxia

for

several

hours

before

beingtransferred

to

anoxia

increases

the

ability

of

roots

forlactateeffluxand

prolongs

survival.Ethylene

promotes

long-term

acclimativeresponses:including

formation

of

aerenchyma

and

stemelongation

Treatment

ActionEffect

on

aerenchymadevelpmentHypoxiaHypoxia

+

Ag+

Hypoxia

+

AVGHypoxia

+

EGTANormoxia

+

ethyleneNormoxia

+

caffeineStimulates

ETH

productionInhibits

ETH

actionInhibits

ETH

synthesisChelates

Ca2+Induces

ETH

responseIncrease

cytosolic

Ca2+PromotedReducedReducedReducedPromotedPromoted(A)

Formationof

aerenchyma

is

stimulated

byhypoxia

but

not

by

anoxia.Role

of

ethylene

in

promotion

of

long-termacclimative

responses(B)

Transduction

of

low

O2

signal

in

maize

leads

to

PCDduring

the

formation

of

lysigenous

aerenchyma.Chemicals

that

increase

the

cytosolic

Ca2+concentration

under

aerobic

conditions

promoteaerenchyma

formation,

whereas

compounds

that

blockCa2+

movement

under

anoxia

inhibit

aerenchymaformation.第五節(jié)鹽害(salt

stress)與植物的抗鹽性Areas

of

greatest

aquifer

depletion,

saltwater

intrusion

agroundwater

contamination

in

US.High

salt

concentrations

in

the

rhizosphere

generatestress

through

water

deficits

and

ion

toxicity.Exclusion

of

salt

and

osmotic

adjustment

both

playmajor

roles

in

tolerance

of

high

salt

environments.Areas

with

high

salinity:Coastal

salt-marshes;Islanddeserts;Near

the

shores

of

island

lakes

;Crop

fields

with

extensive

irrigation.In

China,

more

than

7

million

hectares

are

classified

assaline,

much

of

this

resulting

from

centuries

ofirrigation.A

New

England

salt

marsh

is

one

highly

productiveestuarinehabitat.

Theprimary

producers

are

phytoplankton,

algae,

and

salt-tolerant

plants

sucmarsh

grass

(Spartina).

Chesapeake

Bay,

Mobile

Bay,

and

San

Francisco

Bayare

broad,

shallow

estuaries.

In

tropical

regions,

mangrove

swamps

functimuch

like

salt

marshes

in

estuarine

ecology.Consequences

of

Heavy

Irrigation

-----

salinization

Irrigated

crops

in

the

Sahara

?Desert,

inAlgeria.Extensive

irrigation

leads

tosignificant

increase

in

the

saltcontent

of

agricultural

soils.Halophytes:

plants

that

grow

in

high-salt

soils濱藜（海馬齒）：生活于歐洲、地中海、北非與南非等海邊的鹽生植物?Idealized

growth

responses

ofhalophytes,

salt-tolerantnonhalophytes,

and

sensitivenonhalophytes

to

saltconcentration.Role

of

osmotic

adjustment

in

salt

tolerance

Osmoti