This document provides an outline and overview of heat stress on plants. It begins with an introduction that defines heat stress and its effects on plant growth and development. It then discusses the perception of high temperature in plants and their responses, including morphological, physiological and molecular adaptations. The mechanisms of heat tolerance are also examined, particularly the role of heat shock proteins in protecting plant cells from damage. The document concludes that plants can adapt to heat stress through antioxidant protection and heat shock proteins maintaining protein stability.

1. ADJIBOGOUN Rodrigue: 10704544
DIAW Faty: 10747923
ABAH Simon Peter: 10747927
HEAT STRESSES ON
PLANT
Presented by Group Two
Course Title/Code: Physiology of Abiotic stresses (WACI704)

2.  Introduction
 Effects of heat stress on plant
 Perception of plant to high temperature
 Response to heat stress
 Mechanism of heat stress
 Conclusion
OUTLINE

3. INTRODUCTION
 Heat stress can also be called high
temperature stress
 Heat stress (HS) is a major environmental
stress that limits plant growth, metabolism,
and productivity worldwide (Hasanuzzaman
et al., 2013)
 Plant growth and development involve
numerous biochemical reactions that are
sensitive to temperature.

4.  HS is a major concern for crop production and approaches
for sustaining high yields of crop plants under HS stress are
important agricultural goals.
 Plant responses vary with the degree and duration of HS
and the plant type.
 Plants possess a number of adaptive, avoidance, or
acclimation mechanisms to cope with HS situations
 Plant survival under HS depends on the ability to perceive
the HT stimulus, generate and transmit the signal, and
initiate appropriate physiological and biochemical changes.
INTRODUCTION

5. INTRODUCTION
0 – 100C 10 – 300C 30 – 650C
Classification of plant according to
temperature of growth by Laucher 1995

6. Ranges of temperature for seed germination of different crops

7. Major effects of high temperature on plants
Effect of high temperature on plant
 Plant can operate most of its
physiological process normally
in the range of 0-40 0C
 High temperature stress >
400C causes injury to the
plant
 The degree and duration of
exposure also increase the
effect on plant.

8.  Heat stress affects various
biomolecules
 Plants are static poikilotherms
 Plant can sense mild change
in the ambient temperature.
Effect of high temperature on plant

9. Effect of high temperature on plant
Photosynthesis and growth
 C3 plant are more susceptible to
high temperature stress than C4
plants
 High temperature cause injuries
to chloroplast by:
 Altering structural organization
of thylakoids
 Swelling of grana.
 Impairing grana stacking ability

10. Effect of high temperature on plant
Photosynthesis and growth
High temperature stress
affects
 Photosynthetic pigments
 Activity of photosystem II
 Leaf water potential
 Stomatal conductance
 Intercellular CO2
concentration
 Transcription and activity
of RuBPCase and
RuBPCase activase

11. Effect of high temperature on plant
Photosynthesis and growth
High temperature stress affects
 Leaf area
 Stalk length
 Total biomass
 Number of tillers

12.  Reduce flower buds production
 Increase flower abortion
 Impaired fruit and seed set
Plant reproductive development
Effect of high temperature on plant

13. Effect of high temperature on plant
 Generation of Reactive
Oxygen Species (ROS)
 Oxidation of protein, poly
unsaturated fatty acids,
and DNA
 Activation of programmed
cell death
Plant metabolism

14. Perception of high temperature on plant

15. Plant Responses to Heat stress
Morphological Physiological
Molecular
 Anatomical changes
 Phenological changes
 Water relations
 Osmolytic reaction
 Hormonal changes
 Oxidative stress

16.  Scorching of leaves and twigs
 Sunburns on leaves branches and stems
 Leaf senescence and abscission
 Shoot and root growth inhibition
 Fruit discolouration and damage
 Reduction in the internodes length
 Reproductive phase most sensitive to high temperature
are gametogenesis (8 – 9 days before anthesis) and
fertilization (1 – 3 days after anthesis) in various crop
plants (Foolad, 2005).
Morphological Symptoms

17. Morphological Symptoms
Scorching of leaves Sunburns on leaves Desiccation tolerance Fruit discolouration and
damage
Leaf senescence
Leaf abscission

18.  Reduced cell size
 Closure of stomata and curtailed water loss
 Increased stomatal and trichomatous density
 Greater xylem vessels of both root and shoot
 Damaged the Mesophyll cells and increased permeability of
plasma membrane.
 Reduced photosynthesis by changing the structural
organization of thylakoids (Karim et al., 1997)
 Loss of grana stacking or its swelling.
Anatomical Changes

19.  High temperature can damage leaf gas exchange properties
during vegetative stage
 increase flowers abortion during reproduction
 Impairment of pollen and anther development
 Decrease in days to ear emergence, anthesis and maturity
in wheat
 Grain filing duration is also decreased.
Phenological changes

20. Plant - waters relations:
 distrubed the leaf water relations and root
hydraulic conductivity (Morales et al., 2003)
 Enhanced transpiration induces water deficiency in
plants causing a decrease in many physiological
processes (Tsukaguchi et al., 2003).
 High temperature causes water loss in plant more
during day time than night time.
PHYSIOLOGICAL RESPONSES

21. Plant species may accumulate osmolytes such as:
Accumulation of compatible Osmolytes

22. MOLECULAR RESPONSES
 Heat stress may induce oxidative stress
 Activated oxygen species = autocatalytic peroxidation of
membrane lipids and pigments = loss of membrane semi-
permeability and modifying its function.
 Super oxide radical (O2-)
 Hydrogen peroxide (H2O2)
 Hydroxyl radical (OH-)
 The scavenging of O2
- by superoxide dismutase (SOD) results in
the production of H2O2, which is removed by Ascorbate
peroxides.
Note: Protection against oxidative stress is an important
component in determining the survival of a plant under
heat stress.

23. Different adaptation mechanisms of Plant to Heat Stress
Avoidance Mechanisms
Under HS conditions, plants exhibit various mechanisms for
surviving which include:
 long-term evolutionary phonological and
 morphological adaptations and
 short term avoidance or acclimation mechanisms
Tolerance Mechanisms
The ability of the plant to grow and produce economic yield
under HT
MECHANISM OF HEAT TOLERANCE:
How do plants overcome heat stress?

24. Avoidance Mechanisms
Tomentose leaves Rolling of leaves

25.  Schematic diagram showing the molecular regulatory mechanism of heat shock proteins
based on a hypothetical cellular model.
 Entry of monomeric heat shock
factors (HSFs) to nucleus
 Trimerization of HSF monomers
 Binding of active trimer to the
specific genomic region
 Transcription, translation and
post-translational modification
 Production of functional HSPs
Tolerance Mechanisms

28.  In general, heat stress is responsible for the up-regulation
of several heat inducible genes, commonly referred as
“heat shock genes” (HSGs) which encode HSPs and these
active products are very much necessary for plant’s survival
under fatal HT (Chang et al., 2007).
 This help to protect intracellular proteins from being
desaturated and preserve their stability and function
through protein folding; thus it acts as chaperones (Baniwal
et al., 2004)
Molecular regulatory mechanism of
heat shock proteins

29. Summary of adaptation to heat stress

30. Conclusion
HT is one of the major abiotic stress
Affect plant photosynthesis, growth, development,
reproduction and metabolism.
Plant can adapt to high temperature:
 activity of antioxidant enzyme and antioxidant
metabolite work as scavenging and protect plant
from oxidative damage
HSP initiate protein folding that protect protein from
denaturing and restore stability under heat stress