高级植物生理学课件-ppt-word

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四、根系对水分的吸收

water-channel proteins (aquaporins)

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in cell walls of exodermis and endodermis blocks

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Water must

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the cells (symplasm)

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Plasma membrane offers enormous resistance to water transport

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How can water enter the symplast?

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Through special pores in the plasma membrane:

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Water transport across membrane is mediated by water channels (aquaporins)

Water movement

–

ALWAYS PASSIVE !

Water movement occurs either as diffusion or bulk flow

Diffusion: driven by concentration gradient, permeability defined as diffusional water permeability

(Pd: m s-1)

Bulk flow: driven by pressure difference (hydrostatic or osmotic); defined as osmotic permeability (Pf:

m s-1) or hydraulic conductivity (Lp:m s-1 MPa-1)

Pf often greater than Pd, Why ?

Water channels -Aquaporins

?

Transmembrane proteins;

?

Facilitate passive transport of water; 10-1000 fold higher than lipid permeability.

?

Can be highly selective to water (true aquaporins).

?

Some can be more selective for small neutral solutes (eg. glycerol; aquaglyceroporins)

?

Some

animal

aquaporins

have

recently

been

shown

to

create

ion

channels

under

certain

conditions.

Aquaporins can also mediate flux of other substances across cell membranes

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Water and CO

2

conductivity

?

Plant aquaporins conduct

water or CO2

?

Aquaporin CO2 conductivity is significant for photosynthesis

Activities of aquaporins are reflected by permeability to water (P

f

or Lp).

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五、植物吸收水分的来源

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六、干旱及植物的适应性反应

当植物 耗水大于吸水时，使组织内的水分亏缺。过渡水分亏缺的现象称为干旱。干旱

可分大气干 旱和土壤干旱。大气干旱的特点是大气温度高而相对湿度低

(10

％－

20

％

)

，蒸腾大

大加强，于是破坏水分平衡。此外，大气温度高，阳光强，也会造成植物的热 害。大气干旱如

果长期存在，会引起土壤干旱。土壤干旱是指土壤中缺乏植物能吸收的水 分的情况。土壤干旱

时，植物生长困难或完全停止，受害情况比大气干旱严重。

干旱对植物的伤害

水分亏缺严重时，植物细胞失去紧张，叶片和茎的幼嫩部分下垂，这种现象称为萎蔫

（

wilting

）。萎蔫可分为暂时萎蔫和永 久萎蔫两种。在炎夏的白天，蒸腾强烈，水分暂时供应

不及，叶片和嫩茎萎蔫

到晚间，蒸腾下降，而吸水继续，消除水分亏缺，即使不浇水也能恢复< /p>

原状。这种靠降低蒸腾即可消除水分亏缺以恢复原状的萎蔫，称为暂时萎蔫

(temporary wilting)

。

如果由于 士壤已无可资植物利用的水，虽然降低蒸腾仍不能消除水分亏缺以恢复原状的萎蔫，

称为 永久萎蔫

(pemanent wilting)

。永久萎蔫时间持续过久，植物就会死亡。

Growth rate of shoot and root of young corn plants in nutrient solution with a defined water potential

Water loss is controlled by stomata on the leaf surface

Guard cells are the only epidermal cells that contain chloroplasts

Stomatal guard cells control stomatal aperture

Stomata open when turgor increases

Orientation of the cellulose fibers in the cell walls allows guard cell expansion in longitudinal

direction only: the aperture increases

Stomata may be on the leaf surface, or ?hidden? in a stomatal crypt (?sunken stomata?)

ABA - a phytohormone involved in acclimation to water stress

Concentration of ABA in xylem exudate and leaves of water stressed sunflower plants (closed

symbols: control; open symbols: water stress)

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86

Demonstration of 10?

M

ABA on

Rb

(K

+

)

efflux from stomata cells .

ABA was added 2min. or 40 min. of wash-out in the absence of ABA

ABA-pathway in a drought stressed plant from root or leaf-mesophyll to the guard cells

The mesophyll cell in the insert shows pH dependent ABA compartmentation.

Only the protonated ABA can pass membranes.

ABA

< br>通过影响保卫细胞的膨压来控制气孔的开关

ABA

对保卫细胞离子运输至少有四种效应：

控 制向内运输的

K+

通道，激活向外运输的

K+

通道，促进

Ca2+

通道的开放 和膜的去极化。

ABA

Ca2+

浓度升高。其效应：< /p>

Ca2+

浓度的提高活化了阴离子通道，从而促进

阴离子的流出，并使膜电势向负值小的方向偏移，这种膜的去极化形成一个有利于

K

＋通过一

种外向的

K

＋通道而被动外流的电化学梯度，

从而促进气孔关闭。

膜的去极化也可阻止

K

＋通过

向内的

K

＋通道而被动吸收，

从而抑制气孔的 开放。

Ca2+

一方面来自质外体，

二是亚细胞器

（液

泡）中释放

受体

R

ABA

结合，

通过

Ca2+

进入细胞或胞内释放

,

Ca2+

增加。

胞内游离

Ca2+

促进

质膜上阴离 子通道和外向型钾离子通道打开，抑制内向型钾离子通道打开。由于出去的钾离子

多于进 入的钾离子，丢失，导致气孔关闭。

ABA is by far not the only reaction of

plants against water stress

Changes

in

xylem

water

potential

and

free

proline

accumulation

in

lemon

tree

leaves

subjected

to

extended water stress

控制性作物根系分区交替灌溉

传统的 灌水方法，追求田间作物根系活动层的充分和均匀湿润，而本方法则强调在土

壤垂直剖面 或水平面的某个区域保持干燥，仅让一部分区域灌水湿润，交替控制部分根系区域

干燥、 部分根系区域湿润，以利于通过交替使不同区域的根系经受一定程度的水分胁迫锻炼，

刺 激根系吸收补偿功能，及作物部分根系处于水分胁迫时产生的根源信号脱落酸传输至地上部

叶片，以调节气孔保持最适开度，达到以不牺牲作物光合产物积累而大量减少其奢侈的蒸腾耗

< br>水而节水的目的。同时还可减少再次灌水间隙期间棵间土壤湿润面积，减少棵问蒸发损失；因

湿润区向干燥区的侧向水分运动而减小深层渗漏。控制性作物根系分区交替灌溉在田间可通过