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The Molecular Mechanism of Abiotic Stress in Plants:A Bird's Eye View

introduction to different stress ,their cause , mechanism of action of different hormones at molecular level....

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The Molecular Mechanism of Abiotic Stress in Plants:A Bird's Eye View

  1. 1. By: Yashdeep Srivastava (J.N.U Ph.D.) Metabolic And Structural Biology Division CSIR-CIMAP
  2. 2. 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
  3. 3. 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
  4. 4. Fig:The complexity of the Plant response to Abiotic Stress
  5. 5. INTERACTIONS BETWEEN ABIOTIC AND BIOTIC STRESSES: Abiotic stresses Drought High salinity Heat Biotic stresses Pathogen Wounding Mechanical Insect Herbivory ROS Accumulation Hormones :ABA Hormones SA,ET,JA,ABA Kinases Transcription Factors MYC,MYB,NAC,ZF,HSF STRESS RESPONSE Fig: Convergence points in abiotic and biotic stress signalling networks
  6. 6. Transcriptional regulation in Abiotic stress Cold Stress Drought(Osmotic) Stress ICE1 CAMTA DREB1A/CBF3 DREB1C/CBF2 DREB1A/CBF3 DREB1C/CBF2 DREB1B/CBF1 DRE/CRT ABA DREB2 AREB/ABFMYB MYCNACZFHD
  7. 7. 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
  8. 8. 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 Vacuole Cytoplasm ABA glucosyl ester ABA β-glucosidase
  9. 9. 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.
  10. 10. 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
  11. 11. 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
  12. 12. 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.
  13. 13. 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
  14. 14. Salt stress increases various secondary metabolites in plants Influence of drought stress on various plant secondary metabolites
  15. 15. 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.
  16. 16. C. plantagineum. Mesembryanthemum crystallinum Thellungiella halophila
  17. 17. 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
  18. 18. 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.

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