The Molecular Mechanism of Abiotic Stresses in Plants:A bird’s-eye view

 

By:

Yashdeep Srivastava(J.N.U Ph.D.)

Metabolic And Structural Biology DivisionCSIR-CIMAP

Though the term “stress” has been defined exactly in mechanics, in the case of biology it

has been given widely different meanings.

Probably due to an extension of the physical meaning, many of these definitions converge

in attributing “stress” to any environmental factor “unfavorable” for the living organism

under consideration.

STRESS

Light and heat stress induces membrane damage and photo inhibition that leads to ROS accumulation.

Drought stress causes stomata closure and photosynthesis impairment which leads to ROS accumulation .

Pollutants such as O3 and suphuric acid, causes acid Rain,and directly damage the leaves and induce oxidative stress on tissues

Soil salinity causes stress which leads to ROS production .High salinity decreases mineral nutrient uptake further stressing the plant.

Cold Stress often alters membrane properties and affect enzymatic activity. Frost damage can cause severe damages to the plant and tissues necrosis.

Mechanical damage ,caused both by abiotic and biotic factors ,induces the expression of defense related functions.

Heavy metals cause cytotoxic effects via different mechanisms such as production of ROS ,blocking of essential functional groups and displacement of essential metal ions from biomolecules.

Water excess causes hypoxia ,programmed cell death and oxidative stress .

Fig. Effect of different types of abiotic stresses

Fig:The complexity of the Plant response to Abiotic Stress

INTERACTIONS BETWEEN ABIOTIC AND BIOTIC STRESSES:

Abiotic stressesDrought

High salinityHeat

Biotic stressesPathogen Wounding

Mechanical Insect

Herbivory

ROS AccumulationHormones :ABA

HormonesSA,ET,JA,ABA

Kinases

Transcription FactorsMYC,MYB,NAC,ZF,HSF

STRESS RESPONSE

Fig: Convergence points in abiotic and biotic stress signalling networks

Transcriptional regulation in Abiotic stress

Cold Stress Drought(Osmotic) Stress

ICE1 CAMTA

DREB1A/CBF3 DREB1C/CBF2

DREB1A/CBF3DREB1C/CBF2DREB1B/CBF1

DRE/CRT

ABA

DREB2AREB/ABFMYB MYCNACZFHD

POST-TRANSCRIPTIONAL REGULATION OF ABIOTIC

STRESS-INDUCIBLE TRANSCRIPTS

RNA helicases are implicated in abiotic stress responses in various organisms including

plants .

Alternative splicing, which enables production of diverse polypeptides from one gene, is

regulated by various abiotic stresses.

Complex multi-step regulation controls the splicing profiles in abiotic stress responses.

Alternative splicing events are considerably conserved between Arabidopsis and rice,

indicating their importance

HORMONE RESPONSE IN ABIOTIC STRESSES:

Rate limiting Enzymes

9-cis-epoxycarotenoid di-oxygenases

(NCEDs) of ABA biosynthesis

P450 CYP707As of ABA catabolism

Rehydration Rehydration

VacuoleCytoplasm

ABA glucosyl-ester

VacuoleCytoplasm

ABA glucosyl ester

ABA

β-glucosidase

ABA receptors

Soluble receptors eg. PYR1, RCAR1, STAT type

Membrane anchored receptors eg. GTG1, GTG2

The downstream signaling pathway has not been fully

elucidated.

Fig.ABA signaling pathway including ABA soluble receptors

ABA

AREB/ABF etc.AREB/ABF etc.

METABOLIC PROFILE CHANGES UNDER ABIOTIC STRESS

Under stress conditions, plants appear to re-organize their metabolic network in

order to adapt to such conditions.

Abiotic Stress

Increased production of

specific desired compounds

Reduction in the level of

toxic compounds

Amino Acid

PROLINE

Salt stress

In Plants Pyrroline 5 carboxylate synthetase

(P5CS)PROLINE

Proline confer a protective effect by inducing stress protective proteins.

Exogenously applied proline and salt stress in Pancratium maritimum were found to induce

the expression of ubiquitin, antioxidative enzymes and dehydrins.

Amines

Glycine-betaine

Salt stress

Suaeda liaotungensis (Halophyte)

Betaine aldehyde decarboxylase

Tobacco Resistant to salt conditions

Choline dehydrogenase gene (codA)

Arthrobactor globiformis

Rice

Choline Glycine-betaine

Resistant to salt conditions

Tomato chloroplast

Tolerant to chilling and

oxidative stress

Salt stress

Polyamines

Arginine decarboxylase, ornithine

decarboxylase and S-adenosyl

methionine decarboxylase

Putrescine,

spermidine,

spermine

Sugar and sugar alcohol

Trehalose (rare non reducing sugar) found in many bacteria and fungi and in some dessication

tolerant higher plants.

Increase in trehalose levels in transgenic plant resulted in higher photosynthetic rate and decrease in

photooxidative damage during stress.

Trehalose has water absorption capacity to protect biological molecule from dessication induced

damage.

Mannitol (ROS scavanger) is another sugar alcohol that accumulate upon salt and water stress.

Metabolite profiling

Arabidopsis

Drought and

heat stress

Maltose and glucose

Proline

Drought stress

Proline

Heat stress : reduces the toxicity of proline

Combination of stress – Sucrose (major osmoprotectant) replaces Proline

Salt stress increases various secondary metabolites in plants

Influence of drought stress on various plant secondary metabolites

Model Plants for study of Abiotic stress responses:

Drought Tolerance:Regular drought tolerant plants can withstand 30% water loss and desiccation tolerant Plant tolerate

90% water loss and have ability to rehydrate successfully so they can used as model plants for

dehydration studies. Ex. C. plantagineum.

Sainity Tolerance :

•Halophytes such as Mesembryanthemum crystallinum (ice plant) is a model C3/CAM plant.

•Salt stress mechanism in this plant were studied with respect to C3/CAM shift and oxidative stress by

characterizing Na +/K+ transporters and aquaporins.

•Thellungiella halophila(salt cress) is closely related to A. thaliana but in contrast to Arabidopsis this

plant tolerates extreme salinity, drought and cold.

•Transcript profiling experiment revealed that salinity induces fewer genes in Thellungiella than in

Arabidopsis and in sat free condition stress related genes in Thellungiella exhibits higher expression .

•Ion channnels in Thellungiella root cells have higher K+/Na + specificity than Arabidopsis.

C. plantagineum.Mesembryanthemum crystallinum

Thellungiella halophila

Identification of sensors and signaling pathways for abiotic stresses.

Understanding the molecular basis of interplay among stresses (including

biotic stresses).

Identification of key factors in the connection between abiotic stress

responses and developmental processes.

Addressing how local abiotic stress signals are processed and transduced to

other parts of the plant body.

Examining long-term plant responses under multiple abiotic stress conditions

in nature.

Establishment of experimental conditions that mimic field conditions.

Future challenges

References:1.Hirayama T. et.al (2010);Research on Plant abiotic stress responses in the post-genome

era :past, present and future. The Plant journal,61,1041-1052.

2.Vincour B. et.al. (2005); Recent advances in engineering plant tolerance to abiotic stress:

achievements and limitations. Current Opinion in Biotechnology, 16,123–132.

3. Gaspar T.et.al.(2002); Concepts in plant stress physiology. Application to plant tissue

cultures. Plant Growth Regulation, 37, 263–285.

4. Matthew A.J. and Hasegawa P. M. (2005); Plant Abiotic Stress. Blackwell Publishing

Ltd.

5.Fujita M. et.al.(2006) ; Crosstalk between abiotic and biotic stress responses: a current

view from the points of convergence in the stress signaling networks. Current Opinion in

Plant Biology, 9,436–442.

6. Wang W et. al.(2003); Plant responses to drought, salinity and extreme temperatures:

towards genetic engineering for stress tolerance. Planta, 218,1-14.

Thank You !