植物学专题讨论二

Initiation and regulation of water deficit-induced ABA accumulation in maize leaves

and roots: cellular volume and water relations

研究生：吕祥勇

导 师：梁建生教授

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Abstract While PEG treatment led to a significant increase of

ABA content in both root and leaf tissues, EG, a permeable monomer of PEG, had no effect on ABA accumulation at similar or much lower osmotic potentials. A rapid and massive accumulation of ABA in leaf tissues occurred at a specific threshold of PEG6000 concentration, about 20%,and closely coincided with the start of the tissue weight loss and the obvious decrease of cellular osmotic potential.

When samples were dehydrated and incubated under pressure, ABA accumulation was similar to those dehydrated and incubated under atmospheric pressure.

Such results suggest that both the absolute water potential and pressure potential per se had no direct effects on the dehydration-induced ABA accumulation.

The initiation of ABA accumulation is related to the weight loss of tissues or changes in cellular volume rather than the cell water relation parameters, and the capability of ABA accumulation can be regulated by cellular osmotic potential.

KEY WORDS:PEG,EG,ABA Water Relations, Maize,

Water deficit-induced ABA accumulation is a key question for revealing the mechanisms of cellular stress signaling.

The relationships between the initiation of ABA accumulation and water relations is not clear.

Earlier research: ABA accumulation was a function of the decrease in total water potential.( mainly focused on the initiation of water deficit-induced ABA accumulation)

Further studies: that was a function of the loss of leaf turgor or the initiation of zero turgor.

Other reports: that might not be initiated at zero turgor under all conditions.

Introduction

干旱 AtHk1G-protein

Arc A protein

Genes 1

Genes-2

Drought response

×

?

?(MAPK)?

?

Proposed drought signalling pathways

ABA

?

ABA

?(MAPK)

Controversy: One parameter of the water relations while overlooking the interactions among others.

PEG and EG are applied. EG: freely permeate cell membranes with adverse effects on the cell physiology. Compare the effects of water potential and cellular turgor potential.

Materials and methods

Plant materialsmaize seeds ,Hoaglands nutrition

solution,28 ,2nd leaf, root tips℃

Measurement of osmotic potential

samples Vacuum infiltrated Various concentration of PEG or EG

25 ,1h℃

Absorbed with tissue paper

Seal in cap vial and frozen

Thaw and collectcell sap

measure

Water deficit treatment

samples Air dehydration30min

Leaf loss 80%Root loss 60%

Seal with AL foilIncubation in

moist chamber25 ,special times℃

Air dehydration

PEG/EG treatments

0.25 ㎝ 2

Leaves squareVacuum

infiltratedPEG/EG solutions Incubation 25℃

Special times

Root tips Various concentration

Dehydration under pressurization

Leaves with whole sheath

Pressure chamber

Applied pressure0.5MPa 5min

Pressure0.8-1.0MPa

10min

ABA analysis ELISA 法测定：

称样 冰浴研磨 震荡过夜 离心 包被

加抗原

水浴

平衡

甩液

加样 加抗体

水浴

洗板加二抗反应洗板显色终止测定

Results

[PEG] ＜ 20%,PEG treatment had no effect on cellular osmolality

[PEG] ›20%,the cells were substantially dehydrated and their sap were concentrated.

EG treatment had no effect on ABA contents in either roots or leaf tissues under all the concentrations tested.

Above 20%[PEG],a clear threshold of PEG concentration, yet not so apparent in the root tissues.

EG did not dehydrate leaf tissues and might have increased the tissue weight at high concentrationsthough the uptake of EG.

The threshold for the PEG-induced ABA accumulation coincided with PEG-induced weight loss.

0.6MEG,increase osmotic concentration ,reduce the PEG-induced ABA accumulation in leaf tissues.

Decrease in air dehydration-induced ABA accumulation in both root and leaf tissues.

Presence/absence of a pressure to dehydrated leaf tissue had no effect on dehydration-induced ABA accumulation.

It is not the loss of absolute pressure inside the cells, as a consequence of turgor loss, that controls the ABA accumulation.

Discussion

Water deficit-induced ABA accumulation is not related to the cellular osmotic potential.

PEG induced a massive ABA but did not change in the cellular osmotic potential.

PEG-induced ABA accumulation occurred just when the weight of leaf tissues and also the cellular osmotic potential

began to decrease.

Initiation of water deficit-induced ABA accumulation in fact was brought about by the loss of weight of the leaf tissues

Q:Water relations parameters ？ Initiation of ABA accumulation, initiation of ABA accumulation occurs at a specific water potential or at zero turgor??

Press-volume curves, first, changes in cellular volume is small, when reach 0,rapidly,0 turgor may reflect the threshold for the significant changes in volume.

Q: The capability of ABA accumulation is regulated? ? ?

None of the water relations parameters is directly involved in the initiation of water deficit-induced ABA accumulation, they modify the capability?

Fig5 :cellular osmotic potential may be related.

The mechanism of the water deficit-induced ABA accumulation is very complex and includes a series of cellular signaling processes. but the triggering mechanisms are still unknown.

The cell membrane is difficult to study water deficit signal perception because water deficit signal can’t be labeled to find its receptors as other signals.

Changes in cellular volume, should be bring about the changes of membrane tension. It might be more likely the real trigger. There might be other mechanisms (action of cell cytoskeleton related to the changes in cellular volume)