presentation on heat stress in respect of plant biology. an insight into the various responses and adaptive mechanisms in plants

1. 1
Credit Seminar on:
Presented By:
Sachin Nagre
M.Sc. (Ag.) Semester: III
Enrollment No.: 180112018
Submitted To:
Department of Plant Physiology
College Of Agriculture, Jabalpur
Heat stress: Plant Responses and Adaptation

2. • Introduction
• Global impact on high temperature stress
• Plant responses to heat stress :-
• A) Growth & Morphological symptoms
• B) Anatomical changes
• C) Phenological changes
• Physiological responses :-
• Water relation
• Photosynthesis
• Accumulation of compatible osmolytes
• Assimilate partitioning
• Cell membrane thermo stability
• Hormonal changes
• Molecular responses :-
• Oxidative stress
• Antioxidant
• Stress proteins
• Mechanism of heat stress and tolerance
• Conclusion
• Case study
Outline

3. Introduction
 STRESS
The overview pressure that effects the normal functions
of individual life or the conditions in which plants are
prevented from fully expressing their genetic potential
for growth, development and reproduction.
(Levitt, 1980 ; Ernst, 1993)

6. High temperature stress
Heat stress can also be called high temperature stress.
Heat stress is often defined as the rise in temperature
beyond a threshold level for a period of time sufficient
to cause irreversible damage to plant growth and
development.

13. A threshold temperature (TT) refers to a value
of daily mean temperature at which a
measurable reduction in growth begins. This is
the range wherein changes in the
photosynthetic capacity are irreversible, but
other characters such as growth, lowering, etc.,
are reversible.
The upper and lower developmental threshold
temperatures are the ones at which growth and
development ceases and they differ based on
the plant species and genotypes.
Every crop plants have threshold temperatures
for different developmental stages, upon
exceeding crop experiences the stress.

14. Crops Threshold
temp. (ͦC)
Developmental stage
Rice 15-35 Germination
33 Biomass
25 Grain formation and yield
34 Grain yield and quality
Wheat 10-35 Germination
20-30 Vegetative
15 Reproductive
35 Postanthesis
35 Protein accumulation
Maize 15-40 Germination
33-38 Photosynthesis
38 Vegetative
36-40 Pollen viability and
fertilization
Sorghu
m
20-40 Germination
26-34 Vegetative
25-28 Reproductive
Crops Threshold
temp. (ͦC)
Developmental stage
Pearl millet 10-34 Germination
Chickpea 10-35 Germination
15-30 Growth
25 Reproductive Growh
Pea 15-20 Vegetative Growth
Soybean 26 Reproductive development
23 Post anthesis
30.2 Pollen Germination
36.1 Pollen Tube Growth
Groundnut 10-41 Germination
29-33 Vegetative Development
25-28 Vegetative Growth
22-24 Reproductive Growth
Lentil 32/20 Reproductive Stage
Cotton 31.8-43.3 Pollen Germination
28.6-42.9 Pollen Tube Growth

17. Plant Responses to Heat stress :-
Seedling Stage :-
 Delayed germination
 Reduced vigour
Vegetative stage :-
 Reduced NAR & RGR
 Small internodes
 Increased tillering
 Early senescence & reduced biomass
Reproductive Stage :-
 Reduced flower buds production
 Increased flower abortion
 Impaired fruit & seed set
 Impaired meiosis in both male & female part of plant.
 Impaired pollen germination and pollen tube growth
 Reduced ovule viability

18.  Gametogenesis and fertilization are the reproductive
phase which are most sensitive to high temperature in
various crop plants (Foolad, 2005).
 The reproductive tissues are the most heat sensitive.
Few degrees elevation in temperature during flowering
time can result to the loss of entire grain crop cycles .
 During reproduction, a short period of heat stress can
cause significant decrease in floral buds and flowers
abortion. Although great variations in sensitivity
within and among plant species and variety exists.
 Even heat spell at reproductive developmental stages
plant may produces no flowers or flowers may not
produce fruit or seed

21. The morphological symptoms of heat stress
include :-
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

23. Anatomical Changes :-
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

24. Phenological Changes :-
Heat and high temperature can damage
Leaf gas exchange properties during vegetative stage
Opened flowers abortion during reproduction
Impairment of pollen and anther development
Earlier heading is advantageous in the retention of
more green leaves at anthesis, leading to a smaller
reduction in yield (Tewolde et al., 2006)
Decrease in days to ear emergence, anthesis and
maturity has been reported in wheat
Grain filing duration is also decreased.

25. Physiological responses
Water relations :-
 Heat stress perturbed the leaf water relations
and root hydraulic conductivity (Morales et al.,
2003)
 Enhanced transpiration induces water
deficiency in plants, causing a decrease in water
potential and leading to perturbation of many
physiological processes (Tsukaguchi et al., 2003)
 High temperature seem to cause water loss in
plant more during day time than night time

27.  Photosynthesis :-
Photosynthesis is one of the most heat sensitive
physiological processes in plants.
High temperature has a greater influence on the
photosynthetic capacity of plants especially of C3
plants than C4 plants.
In chloroplast, carbon metabolism of the stroma
and photochemical reactions in thylakoid
lamellae are considered as the primary sites of
injury at HTs, Thylakoid membrane is highly
susceptible to HT.

28.  Some other reasons believed to hamper
photosynthesis under heat stress
Reduction of soluble proteins, Rubisco binding proteins
(RBP), large sub units (LS), and small-subunits (SS) of
Rubisco in darkness, and increases of those in light.
 High temperature also greatly affects starch and sucrose
synthesis, by reduced activity of sucrose phosphate synthase,
ADP-glucose pyrophosphorylase, and invertase.
Heat imposes negative impacts on leaf of plant like reduced
leaf water potential, reduced leaf area and pre-mature leaf
senescence which have negative impacts on total
photosynthesis performance of plant.
 Under prolonged heat stress depletion of carbohydrate
reserves and plant starvation are also observed.

29.  Assimilate partitioning :-
• Photosynthesis optimum at 25-30˚C
• Phloem loading-30˚C optimum
• Rate of movement of assimilate from stem upto
50˚C normal.
• Phloem loading is mostly affected.

30.  Accumulation of compatible
osmolytes
 Plant species may accumulate osmolytes such as :-
 Sugars and sugar alcohols ,
 Proline,
 Ammonium compounds,
 Sulphonium compounds (Sairam and Tyagi, 2004)
 Glycinebetaine (GB), an amphoteric quaternary amine,
plays an important role as a compatible solute in plants
(Sakamoto and Murata, 2002)
 High level of GB accumulation was reported in maize
(Quan et al., 2004) and sugarcane (Wahid and Close,
2007)

31. • In contrast, some plant species naturally do not
produce Glycine betaine under stress conditions.
• Proline widely occur and accumulates in higher plants
in response to environmental stresses (Kavi Kishore et
al., 2005).
• Under high temperatures, fruit set in tomato plants
failed during the reproductive development (Sato et
al., 2006).
• Other osmolytes, γ-amino butyric acid (GABA), a
non-protein amino acid, act as a compatible solute.

32.  Primary sites of injury at high temperatures
• Photochemical reactions in thylakoid lamellae
• Carbon metabolism in the stroma of chloroplast
(Wise et al., 2004)
• In tomato, genotypes differing in their capacity
for thermo tolerance as well as in sugarcane, an
increased chlorophyll a:b ratio and a decreased
chlorophyll:carotenoids ratio were observed in
the tolerant genotypes under high temperatures
• High temperature influences the photosynthetic
capacity of C3 plants more than in C4 plants.
(Todorov et al., 2003)

33.  Cell membrane thermostability
• Heat stress accelerates the kinetic energy and
movement of molecules across membranes
thereby loosening chemical bonds within
molecules of biological membranes.

34. Hormonal changes
• Hormones play an important role in this regard. Cross-talk in
hormone signaling reflects an organism’s ability to integrate
different inputs and respond appropriately.
• A gaseous hormone, ethylene regulates almost all growth and
developmental processes in plants, ranging from seed
germination to flowering and fruiting as well as tolerance
to environmental stresses.
 Abscisic acid (ABA) and ethylene (C₂H₄), as stress hormones
 They are involved in the regulation of many physiological
processes
 Acting as a signal molecules
 At high temperature - level of ABA increases
 Action of ABA :- • Involves modification of gene expression
• Modulating the up or down-regulation of
numerous genes (Xiong et al., 2002).
 High temperature – level of ethylene increases
 Action of C₂H₄ - Induced abscission of reproductive organs

35.  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.

36. Oxidative Stress :-
Production of ROS :-
The main source of ROS production in plants and
the reaction centers of PSI and PSII is in
chloroplasts, also generated in other organelles
viz. mitochondria, plasma membrane, cell wall,
apoplast and peroxisomes
ROS include : O₂, O₂˙‾, H₂O˙, H₂O₂, OH˙,
RO˙organic hydroperoxide (ROOH), excited
carbonyl (RO˙), etc.
They cause damage to biomolecules like
proteins, lipids, carbohydrates, and DNA, which
ultimately results in cell death

37. Advantages Disadvantages
Regulation of signal
transformation and
transcription
Protein kinase cascades
Transcription factors
Transcription
Oxidative stress
Molecular damage (lipids and
fatty acids , proteins, nucleic
acids and pigments)
Cellular damage (membrane
damage, loss of organallae
function. Reduction in
metabolic efficiency ,electrolyte
leakage)
Cell death
ROS

38.  Production of ROS
Mitochondria
Complex 1. NADH dehydrogenase segment
Complex 2. reverse electron flow to complex 1
Complex 3. ubiquinone-cytochrome region
Enzymes: Aconitase, 1-galactono-y
Lactone, dehydrogenase (GAL)
Chloroplast
PSI: electron transport chain
Fd, 2Fe-2S, AND 4Fe-4S
clusters
PSII: electron transport chain
QA and QB
Chlorophyll pigments
Plasma membrane
Electron transporting
oxidoreductases
NADPH oxidase, quinone
oxidase
Peroxisome
Matrix : xanthine oxidase
(XOD)
Merabolic processes: glycolate
oxidase, fatty acid oxidation,
flavin oxidase, disproportion of
O2
-- radicals
Cell wall
Cell-wall-associated
peroxidase
Diamine oxidases
Apoplast
Cell-wall-associated
oxalate oxidase
Amine oxidases
Endoplasmic reticulum
NAD(P)H-dependent electron
transport system
• Flavoproteins
• cyt b5
• cyt P450
ROS

39. LIST OF HEAT SHOCK PROTEINS
Protein class Size (kDa) Location
HSP 100 100-114 Cytoplasm
HSP 90 80-94 Cytoplasm, Endoplasmic
Reticulum (ER)
HSP 70 69-71 Cytoplasm, Endoplasmic
Reticulum (ER),
Mitochondria
HSP 60 10-60 Chloroplast, Mitochondria
smHSP 15-30 Cytoplasm, Endoplasmic
Reticulum (ER),
Mitochondria, Chloroplast

40.  Classification of plants on the basis
of their heat tolerance
Plants
Psychrophiles Mesophyles Thermophyles
Heat-sensitive
species
Relatively heat-
resistant
Heat-tolerant
species

45. Conclusion:
 Plants exhibit a variety of responses to high
temperatures
 High temperatures affect plant growth at all
developmental stages
 Stress proteins are helping in folding and unfolding of
essential proteins under stress, and ensuring three-
dimensional structure of membrane proteins for
sustained cellular functions and survival under heat
stress
 The induction of signaling cascades leading to
profound changes in specific gene expression is
considered an important heat stress adaptation

46. Thank You !
for being a part of today’s
seminar
Sachin Nagre
Enrollment No.: 180112018