The document discusses various types of stress that can affect plants, including biotic stress from pathogens and abiotic stress from physical and chemical factors like drought, flooding, temperature extremes, light levels, salt levels, air pollution, wind, and nutrient deficiencies or toxicities. It describes how each stress can impact plant growth and physiology and outlines some strategies plants use to tolerate or avoid stress, such as escaping the stress period, avoiding stress through morphological adaptations, or tolerating stress through physiological and biochemical mechanisms.

2. Stress
 Any deviation in optimal condition of any factor essential for
its growth will lead to aberrant change in physiological
processes and due to this plant body will experience tension
and this state referred as plant stress.
Reduction in growth, yield and death of the plant or plant part.
Stress may be caused due to biotic (disease, herbivores) or
abiotic (Physical and chemical) factors(Nilsen & Orcutt, 1996).

3. ABIOTIC STRESS BIOTIC STRESS
(A) Physical stress (B) Chemical stress
 Drought and Flooding
 Temperature
 Light
 Radiation
 Wind
 Air Pollution
 Heavy Metals
 Pesticides
 Insecticides
 Toxins
 Soil pH
 Alkanity
 Allelopathy
 Competition
 Disease
 Pest
 Human activities
Classification of stress

4. Strategy to face the stress conditions
 Escaper: Completing their life cycle before the
occurrence of a stress
 Stress Avoider: Achieved through morphological changes
in the plant, such as reduced stomatal conductance,
decreased leaf area and increased root/shoot ratios.
 Stress Tolerant: Sustain the effect of stress without dying
or suffering injury. Achieved by specific physiological,
biochemical and molecular mechanisms at cell level
which include specific gene expression and accumulation
of specific proteins.

5. Major stresses occurred in plants
(1) Water Stress: The availability of excessive (flooding) or
inadequate (drought) supply of water is called the water
stress
Changes in plant growth
 Loss of turgor that affects the rate of cell expansion and
ultimate cell size.
 Affects translocation indirectly by altering the source to sink
relationships for assimilates.
 Changes in structure of macromolecules by removal of water
 Inhibition of cell expansion results in a slowing of leaf
expansion.
 The dehydration of mesophyll cells inhibits photosynthesis

6. Conti..
 Decrease in turgor causes stomatal closure
 ABA inhibits shoot growth, further conserving water and root
growth appears to be promoted,
Osmotic adjustment-Certain organic compounds such as
sucrose, amino acids (especially proline and betaine), inorganic
ions (especially K+) and several others that lower the osmotic
potential and thus, maintain water potential of cells without
limiting enzyme function.

7. Loss of turgor Impaired mitosis
Drought stress
(Reduced water availability)
Obstructed
cell elongation
Diminished
growth
Limited
cell division

9. (2) Salt stress
Affects plants adversely in two ways:
(i) High solute content in rooting medium creates water stress by decreasing
osmotic potential and
(ii) Direct toxic effect of higher concentration of ions.
(1). Halophytes can grow comfortably in saline soils with high salt
concentrations.
(2). Glycophytes: Cannot grow in the presence of high concentrations of salts .
But manage to grow in saline conditions by adopting some mechanisms
as :
 Accumulation of sugars in leaves
 Compartmentalization (checked from reaching to photoshythetic parts)
(Jacoby, 1965)

10. Mechanisms of Tolerance
l. Succulence that may lead to dilution of intracellular salt
such as occurs in Salicorma sp.
2.Presence of salt excreting glands that reduce the
concentration of salt in the plant e.g. Frankenia, Spartina
3.Development of small leaves, water storage hairs and
aerenchyma
4. Sometimes there is synthesis of organic solutes that aids
in the maintenance of turgor

11. Difference between salt stress from ion
stress
1.Salt Stress: If the salt concentration is high enough to
lower the water potential by 0.05 to 0.1 MPa then the
plant is under water stress
2. If the salt concentration is not this high the stress is ion
stress and may be caused by one particular species of ion

12. (3) Temperature Stress
Divided into the effects of temperature that cause
1. High temperature injury
2. Chilling injury
3. Freezing injury

13. High temperature injury
 Respiration rate increases and photosynthetic rate decrease,
tissue may deteriorate because the lack of life supporting
energy
 The denaturation and aggregation of proteins occur
 RUBISCO and other enzymes of carbon metabolism are
adversely affected
 Change in the viscosity of the lipid components of the cells to a
more fluid state
 High temperatures reduce the membrane stability of various
cellular membranes causing loss of physiological functions and
cell integrity
Some plants avoid high- ~temperature injury
 Angle and arrangement of the leaves
 Thick cuticle and leaf hairs (improves conductive cooling)

14. Chilling injury :Injury which causes due to low but
above zero degree centigrade temperature is called
chilling injury.
These chilling temperatures are too low for normal growth but
not enough for ice formation
 Roots are chilled, the plants may wilt
 The chilling sensitive physiological functions include
inhibition of photosynthesis, reduced carbohydrate
translocation, lower transpiration rates, inhibition of
protein synthesis and increased degradation of existing
proteins

15. Freezing injury: occurs at temperatures below the
freezing point of water (below 00C) and primarily the
aqueous phase in the apoplast freezes.
 At 0°C there is a phase transition in water from liquid to
solid. Ice crystals develop in the intercellular spaces and
cell walls
 large polysaccharides and proteins facilitate ice crystal
formation, which are called as ice nucleators

16. (4) Light Stress:
Alteration in light intensity whether a deficit or excess,
will result in a disruption of plant metabolic processes.
 Low light intensities below the compensation point lead
to starvation with carbohydrates used as substrate for
respiration first and then other source of energy.
 In high intensity light photosynthetic performance of
plants is depends upon relationship between photo
inhibition of photosynthesis and the degree of chlorophyll
destruction.

17. Ultraviolet radiation
 The electromagnetic radiation from the sun contains about
7% ultraviolet at sea level. Alteration of protein and lipid
membrane components by ultraviolet may alter membrane
permeability and ionic balance. Such events also cause an
inhibition of photosynthesis and respiration

18. (5) Nutrient Stress
 If plant takes less than optimum quantity of any essential
mineral than the situation is referred as deficiency and more than
optimum than situation is referred as toxicity of that mineral
Deficiency (nutrient Stress) of an element results from:
 Amounts and concentrations present in the soil
 Form in which they exist
 Soil pH

19. Conti…
 Elements such as calcium, boron, and iron often become
deficient in the younger parts of the plant because of little or no
retranslocation and poor phloem mobility. Similarly if such
ions are applied foliarly there is little basipetal movement.
Deficiency Symptoms
 A symptom is any perceptible change in known structure
appearance or function. Such things as leaf yellowing
(chlorosis), death (necrosis), lesions, malformations, reduced
Growth and yield are all considered to be symptoms and occur
as a result of nutrient deficiency. Toxic level of Zink, Copper
and Nickel occurs frequently in soil.

20. (6)Wind
 Excessive water loss through transpiration causes partial
or complete closure of the stomata may ensue which will
restrict the diffusion of carbon dioxide into the leaves. As
a result, there will be a decrease in the rate of
photosynthesis, growth and yield (Edmond et al., 1978).
 Lodging or toppling of plants.

21. (7) Air Pollution
Chemical Symptoms Sensitive Plants
Chlorine
Bleaching, leaf tip and margin browning,
drooping of leaves, yellow spots
Peach, Oak, Pine
Fluorides
Leaf tip and margin yellowing (chlorosis),
dwarfing, leaf abscission, decreased yield
Grape, Blueberry, Apricot
Nitrogen
oxides
Brown spot on leaf, suppression of
growth
Apple, Pinto beans
Sulphur
dioxide
Bleached spots on leaf, chlorosis, early
abscission, reduced yield
Apple, Oats, Pumpkin
Ozone
Reddish brown flakes on leaf surface,
bleaching, suppression of growth, early
abscission, premature ageing
Apple, Grapes, Pine

22. Some examples of air pollution:
 Citrus fruits is extremely sensitive to fluoride
 Cotton is very sensitive to ethylene
 A crop in a tightly closed greenhouse will soon deplete the
CO2 concentration which reduces growth and production
by slowing or stopping photosynthesis

23. Biotic Stress
 Biotic stress is stress that occurs as a result of damage
done to plants by living organisms, such as bacteria,
viruses, fungi, parasites, beneficial and harmful insects,
weeds, and cultivated or native plants.

24.  Mechanical barriers
1. Cork Layers : Formation of cork cells in areas surrounding
penetration points and forming a necrotis spot and the isolation by
cork layers.
2. Tyloses: Restricts pathogens transport through xylem vessels
3. Lignitubers : A sheath, may form around the invading hypha
increasing the mechanical strength of cell walls
 Biochemical resistance
 Passive – already present in plants (Phenolic Glucosides,
Glucose Esters etc) and toxic to potential invaders
 Active – induced by pathogen invasion (Caffeic Acid,
Scopoletin and Orchinol)
Disease control strategies in plants

25. Conti…
 Hypersensitive response (HR): Limited no. of cells
die, pathogen get isolated in localized necrotic tissue
 Phytoalexins: low molecular mass secondary
metabolites with antimicrobial activity
(Hückelhoven, 2007)