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