Plant physiology and ecology

1. UNIVERSITY OF EDUCATION
TOWNSHIP CAMPUS LAHORE
BS BOTANY 3rd
SEMESTER
COURSE TITLE:
Plant Physiology and Ecology (BOTN1116)
SUBMITTED TO:
Mr . Sheeraz Usman
SUBMITTED BY:
Kishaf Maqbool
Ishmal Aijaz
Khadija Dilmeer
Fahad
Atta Rasool

2. Presentation Topic:
Ecophysiological Responses of Plants
in relation to Light and Temperature
Contents:
 Introduction
 Eco-Physiological responses of Plants
In terms of Light: In terms of Temperature:
 Photosynthesis * Photosynthesis
 Opening and Closing of * Respiration
Stomata
 Phototropism * Growth and
Development
 Photoperiodism * Thermal Stress
Responses
Presentation Title :
Eco-Physiological Responses of Plants in
relation to Light and
Temperature

3. Definition of Eco-Physiology:
“ Eco-Physiology/Environmental
Physiology is a biological discipline that
studies the adaptations of an organisms
physiology to environmental
conditions.”
Factors that Effect Plants:
Light Water
Temperature Nutrition

4. Light Responses:
Photosynthesis:
 Light is the primary source of energy for
photosynthesis in plants.
 Synthesis of sugar/food molecules in the presence
of sunlight.
 Most leaves get saturated with only about 20% of
of full sunlight.
 Of this quantity only 4% is stored in sugars.
 Leaves in shade produce little sugar since they
receive limited energy supply.
 Chlorophyll is the main pigment involved
in capturing light energy for photosynthesis.

5. Opening and Closing of Stomata:
 Plants optimize photosynthesis by adjusting leaf angle, size
and chlorophyll content based on light availability. When light intensity is high
potassium ions move into guard cells. This movement of potassium ions causes the
stoma to open.
When the potassium ions move into the guard cells they increase the concentration.
This causes water to move into the guard cells from more dilute areas by osmosis.

6.  Stomatal pores open when guard cells enlarge
as a result of water absorption and close when
guard cells shrink.
 The opening and closing of stomata will also
depend on factors such as light, temperature,
carbon dioxide, and humidity.
 Stomata open in response to light, including
blue light.
 Blue light as a signal induces
stomatal opening.
 When the stomata are open there is an
increase in water lost from the plant,
thus less available for the light reactions.

7. Phototropism:
 One important light response in plants is phototropism, which involves
growth toward or away from a light source.
 Positive phototropism is growth towards a
light source.
 Negative phototropism is growth away from
light.
 Auxins are the main hormones responsible for cell
elongation in
o Phototropism :
(movement in response to light)
o Gravitropism / Geotropism:
(movement in response to gravity)

8. Photoperiodism:
Photoperiodism is the response of plants and animals to the length of
daylight, which affects their growth, development, and behavior.
Types of Photoperiodism:
1.Short-day plants (SDP):
Flowering induced by short days
(e.g., rice)
2.Long-day plants (LDP):
Flowering induced by long days
(e.g., lettuce)
3. Day-neutral plants (DNP):
Flowering not affected by day length
(e.g., tomatoes)

9. Effects of Photoperiodism:
 Flowering and fruiting
 Seed germination
 Leaf growth
 Stem elongation
 Root development
 Hormone regulation
(e.g., auxins, gibberellins)

10. Temperature Responses:
Photosynthesis:
 At low temperatures, the rate of photosynthesis
is limited by the number of collisions between
enzymes and substrate.
 As temperature increases the number of
collisions increases, therefore the rate of
photosynthesis increases.
 However, at high temperatures, enzymes are
denatured.
 During photosynthesis, a temperature of
more than 40 °C slows down the process.
 Each plant species has optimal temperature range for photosynthesis.
 The temperature required for photosynthesis
varies from 10°-40° C depending upon the habitat.
 The optimum temperature required for photosynthesis ranges 25°-35° C.

11. Respiration:
 Respiration rates typically increase with temperature,
affecting energy availability and carbon balance.
 Higher temperatures can lead to increased metabolic
rates, potentially out packing photosynthesis.
 The cellular respiration in plants increases with an
increase in temperature until the point- when a
further increase in temperature will lead to tissue
deterioration.
 When the temperature is decreased, the molecular
energy of the reactants is decreased.
 Low temperatures decrease cellular respiration
in living tissues.

12. Growth and Development:
 Temperature influences flowering time, seed germination, and growth rates.
 Warmer temperatures can accelerate these processes, but may lead
to mismatches with pollinators or other ecological interactions.
 Some plants develop thicker leaves or deeper root systems in response
to temperature changes to better manage heat and water.
 In particular, temperature is a critical factor affecting plant growth.
 Within this range, higher temperatures generally promote shoot
growth including leaf expansion , stem elongation and thickening.
 However, temperatures above the optimal range suppress growth.

13. Thermal Stress Responses:
Heat Stress Responses :
Protein Stability:
 Plants produce heat shock proteins (HSPs)
that help stabilize and refold denatured proteins,
protecting cellular functions.
Antioxidant Production:
 Increased levels of antioxidants (like glutathione)
mitigate oxidative damage caused by elevated
temperatures.
Stomatal Closure:
 To reduce water loss through transpiration,
plants may close their stomata, which can
limit photosynthesis but helps conserve water.

14. Cold Stress Responses:
Cryoprotectants:
 Plants synthesize compounds like sugars and proteins (e.g., antifreeze proteins)
that help prevent ice crystal formation within cells.
Membrane Fluidity:
 Changes in lipid composition of cell membranes occur to maintain fluidity at
low temperatures, ensuring proper function.
Dehydration Tolerance:
 Some plants enhance their ability to tolerate dehydration caused by cold
temperatures through various biochemical pathways.