The challenges of abiotic stress on plant growth and development are evident among the emerging ecological impacts of climate change, and the constraints to crop production exacerbated with the increasing human population competing for environmental resources. These Slides will help you understand such stresses.

1. PLANT ECOLOGY

2. DEPARTMENT OF BOTANY
MUHAMMAD MUBASHIR ALI
BBOF19E001
BS BOTANY 6th (S.S)
SUBMITTED TO:
DR. ABDUL GHANI

3. ASSIGNMENT TOPIC
ADAPTATIONS IN PLANTS AGAINST
ABIOTIC STRESS

4. ABIOTIC STRESS
The negative impact of non-living factors
on living organisms in a specific
environment.
The stresses include drought, salinity, low
or high temperatures, and other
environmental extremes.

5. ABIOTIC
STRESSES
• Drought
• Heat temperature
• Chilling and freezing
• UV radiation
• Salinity
• Heavy metal

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
1. Reduction in water loss:
• Closure of stomata ( reduces
transpiration)
• maintained by ABA
• ABA synthesis - from carotenoid by
ABA synthesizing enzyme in root tip.
• Enters into xylem vessel from root tip to
leaves.
• ABA regulates - metabolism and
stomatal behavior - under water stress.
2. Protection of photosynthetic
machinery:
• Wilting of leaves – protects
Photosynthetic machinery - direct
sun rays.
• Stomatal closure
TOLERANCE
1. Reduction in water loss:
• Closure of stomata ( reduces
transpiration)
• maintained by ABA( Abscisic acid)
• ABA tightly associated with
water availability.
• Enters into xylem vessel from root tip to
leaves.
• ABA regulates - metabolism and
stomatal behavior - under water stress.
2. Protection of photosynthetic
machinery:
• Wilting of leaves – protects
Photosynthetic machinery - direct
sun rays.
• Stomatal closure

8. 3. Osmotic Adjustment :
• Synthesis and accumulate compatible
solutes and ions- under water stress.
• Protect against water loss in leaves.

9. HIGH
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.

10. TOLERANCE
Anatomical changes :
• Reduced cell size
• Closure of stomata
• Curtailed water loss
.

11. Physiological changes :
• Minimize water loss.
• In most species, rate of photosynthesis declines above 35* C.
• As temperature increases- rate of photosynthesis decrease and Dark &
photorespiration increase.
• Integrity and functions of biological membranes - sensitive. As
temperature increase - alters tertiary and quaternary structures of
membrane proteins.

12. 3. Molecular changes:
• Temperature increases- increase HSPs
• production.
• HSPs - associate with particular
structure- cell wall , chloroplast ,
ribosome and mitochondria.
• 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.(0*C – 8*C)
• Below 0*C – Freezing stress. • Chill
sensitive plants- cotton , soybean, maize
and rice.

14. Plants face 3 major problems:
i. Perturbation of membrane.
ii. Slow down - chemical and biochemical
reaction.
iii. Changes in water status and
availability.
• Plants -tolerate -extracellular freezing.
• Intracellular ice crystals – lethal.
• They pierce- plasma membrane.

16. TOLERANCE
1. Stabilization of membrane:
• Changes in lipid composition - increase
membrane stability against freezing stress.
2. Cryopreservation:
• Soluble sugars and other osmolytes have
cryoprotective function.
• They protect cell membranes and organelles
during freezing.
• Sugar replace water and decrease degree of
freeze induced dehydration.

17. 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

18. TOLERANCE
1. DNA Repair:
• UV-B radiation targets DNA.
• UV radiation induces lesions in DNA.
E.g. Pyrimidine dimmers.
• Dimmers – repaired via photorespiration
(photolyase) excision repair.

19. 2. 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.

20. 3. Morphological Changes:
• Leaf curling is a photomorphogenic
response observable at low fluences of
UV-B.
• A protective function – hypothesized -
for leaf or epidermal thickening

21. 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%).

23. TOLERANCE
1. Salt Exclusion:
• Plants can limit salt accumulation in its tissues -by inhibiting- root uptake.
• Strategies evolved - restrict salt transport - into sensitive organs.
2. Salt Excretion:
• Halophytes have anatomical structure – to eliminate excess salt ions.
• Salt glands: Embedded in surface of leaves
• Salt bladders: Specialized trichomes.

25. 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.

26. TOLERANCE
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).

28. THANK YOU