Biotic and Abitic stress response

Biotic and abiotic stress response. Introduction, types of stress and mechanism of tolerance in plants for stress response.

1. Biotic and Abiotic stress response in plants By Keerthana V .

2. Introduction

3. Abiotic stressors

4. Drought Productivity and stability of plants – affected -by water stress. Cell expansion and growth - first processes -to decline under water stress . With progressive water deficit, photosynthesis is adversely affected . Membranes and proteins - damaged by a reduction in hydration and an increase ROS

5. Tolerance Reduction in water loss :  closure of stomata ( reduces transpiration)  maintained by ABA  ABA synthesis - from carotinoid by ABA synthesizing enzyme in root tip.  enters into xylem vessel from root tip to leaves.  ABA regulates - metabolism and stomatal behaviour - under water stress.

6. ii) Protection of photosynthetic machinery :  wilting of leaves – protects photosynthetic machinery - direct sun rays.  stomatal closure iii) Osmotic adjustment :  synthesis and accumulate compatible solutes and ions- under water stress.  proline and glycine betaine – highly compatible solutes – increase cellular osmotic pressure.  protect against water loss in leaves.

7. Heat temperature Serious threat – occurs - plant experience temperature above - adapted. Plant exposed to high temperature – changes occur at molecular level – altering the gene expression. Leads to synthesis - Heat shock proteins . Important adaptive strategy.

8. Tolerance i)Anatomical changes :  reduced cell size  closure of stomata  curtailed water loss ii) Physiological changes :  plant water status - important – water stress.  minimize water loss and synthesize compatible solutes (glycine betaine ).  In most species, rate of photosynthesis declines above 35* C.  As temperature increases- rate of photosynthesis decrease and Dark & photorespiration increase.

9.  Integrity and functions of biological membranes - sensitive. As temperature increase - alters tertiary and quaternary structures of membrane proteins. iii) Molecular changes:  temperature increases- increase HSPs production.  HSPs - associate with particular structure- cell wall , chloroplast , ribosome and mitochondria.  eg . In tomato plant – HSPs aggregate into granular structure in cytoplasm- protects the protein biosynthesis machinery.  other proteins or mRNAs – increase ( not considered as HSPs) - includes – glycolytic enzymes , protein kinases and ubiquitin.

10. Chilling and freezing A bove 0*C or below some threshold temperature (unique for each species) – Chilling stress . Below 0*C – Freezing stress. Chill sensitive plants- cotton , soybean, maize and rice. Plants face 3 major problems:  perturbation of membrane.  slow down - chemical and biochemical reaction.  changes in water status and availability. Plants -tolerate -extracellular freezing. Intracellular ice crystals – lethal. They pierce- plasma membrane.

11. Tolerance i)Stabilization of membrane:  changes in lipid composition - increase membrane stability against freezing stress. ii) Cryopreservation:  soluble sugars and other osmolytes have cryoprotective function.  they protect cell membranes and organells during freezing.  sugar replace water and decrease degree of freeze induced dehydration.

12. UV radiation Reduction in stratospheric O3 - Increase solar UV-B radiation (280-320nm) Cause – decrease in growth and other physiological response in many crops. Tolerance i)DNA repair :  UV-B radiation targets DNA.  UV radiation induces lesions in DNA. Eg . Pyrimidine dimmers .  dimmers – repaired via photorespiration ( photolyase ) excision repair.

13. ii) Accumulation of secondary metabolites :  flavonoids/ anthocyanins – induced by UV-B exposure.  accumulate in epidermis – keep UV radiation away from reaching photosynthetic tissues.  polyamines , waxes, specific alkaloids – contribute –UV tolerance. iii) Morphological changes :  Leaf curling is a photomorphogenic response observable at low fluences of UV-B.  A protective function – hypothesized - for leaf or epidermal thickening

14. Salinity Presence of excess ions – affect many plant processes. Plants are subjected to salinity are subjected to two groups: Halophytes : withstand 20% of salt in soil. Non-halophytes : limited growth – in presence of sodium salt(usually 0.01%).

15. Mechanism of tolerance Minimizing entry and conc. of salt in cytoplasm. Two strategies.. Stress avoidance : barriers that negative effect of stress. Stress tolerance : successful survival despite effect of stress.

16. Salt exclusion : -plants can limit salt accumulation in its tissues -by inhibiting- root uptake. -Strategies evolved - restrict salt transport - into sensitive organs. ii ) Salt excretion : - halophytes have anatomical structure – to eliminate excess salt ions. - salt glands and salt bladders - salt glands: embedded in surface of leaves - salt bladders: specialized trichomes .

17. Heavy metal Gaining importance – impact in human health  food chain. Several vegetables , fruits and cereal crops – accumulate heavy metals. Plants growing on soil – contains high level of metal – metallophytes .

18. Tolerance i) Compartmentation : isolation of metal ions in tissues ( c ell wall of roots and leaves) or cellular compartments (vacuoles) – which are less sensitive to metals. - they are away from metabolically active compartments (cytosol, mitochondria or chloroplast) ii) Metal excretion : - metals –excreted in salt crystals , released through salt glands of some halophytes.

19. Biotic stressers

20. Biotic stressers

21. Biotic stress - occurs as a result of damage done to an organism by other living organisms. (such as bacteria, viruses, fungi, parasites, beneficial and harmful insects, weeds, and cultivated or native plants)

22. Herbivore L ow levels - damage - can be completely compensated by plants in terms of fitness. Further increments - the intensity of damage result in a decreasing ability to maintain complete tolerance

23. Pathogens and parasites Pathogens are the agent that cause infection or disease (microorganism). Host plants have evolved defence mechanisms (i.e . resistance and/or tolerance) against pathogen and parasites attacks . Tolerance -ability to compensate in part for fitness decrements-by pathogens/parasites .

24. Strategies that limit the extent of disease in an infected host B arriers to infection , Immune response rapid cell death in the immediate region around the wound they combat the pathogen by limiting its spread

25. Tolerance Photosynthetic enhancement Growth enhancement Advancing the timing of bud break Delaying the senescence of infected tissue:( due to increased levels of cytokinins ) Increasing nutrient uptake

26. Allelopathy Allelopathy – interference mechanism by which plants release molecules ( allelochemicals )- that affect seed germination , plant phisiology , growth and survival of other plants..

27. Release of allelochemicals into the environment

28. Tolerance of allelopathic compounds in plants Exclusion (root or leaf) Compartmentation ( deposit these compounds in nonmetabolic compartments) (vacuole) Excretion Detoxification

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