The document discusses biotic and abiotic stress responses in plants, detailing various stressors such as drought, heat, cold, UV radiation, salinity, and heavy metals. It explores mechanisms of tolerance, including physiological, biochemical, and genetic changes, as well as adaptive strategies plants employ to cope with these environmental challenges. Additionally, it addresses biotic stressors like herbivores and pathogens, highlighting plant defense mechanisms and allelopathy.

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

2. Introduction
• Productivity , survival,
reproductive biology of plants as
well as crops.
Environmental
stress
• Biotic ( pathogen , herbivore )
• Abiotic (physical environment )
Types
• Physiological, biochemical,
molecular and genetic changes
Mechanism of
tolerance

3. ABIOTIC STRESSERS
• Drought
• Heat temperature
• Chilling and
freezing
• UV radiation
• Salinity
• Heavy metal
BIOTIC STRESSERS
• Herbivore
• Pathogens and
parasites
• Allelopathy

5. Abiotic stressors

6. 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

7. Tolerance
i) 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.

8. 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.

10. 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.

11. 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.

12.  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.

13. Chilling and freezing
• Above 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.

14. 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.

16. 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.

17. 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

18. 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%).

19. 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.

20. i) 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.

22. 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.

23. Tolerance
i) Compartmentation : isolation of metal ions in tissues (
cell 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.

25. Biotic stressers

26. Biotic stressers

27. • 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)

28. Herbivore
• Low 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

31. 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.

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

33. 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

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

35. Release of allelochemicals into the environment

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

38. Thank you