About stress and strain terminology

1. Stress and strain terminology,
Nature of stress injury,
resistance and causes of stress
Vajinder Pal Kalra
Punjab Agricultural University Ludhiana

2. Stress
Stress
• Mechanical force per unit area applied to an object
• Biological stress is not easily defined but it implies
adverse effects on an organism
• Like all other living organisms, the plants are subjected
to various environmental stresses such as water deficit
and drought, cold, heat, salinity and air pollution etc.

3.  Stress is any change in environmental conditions that might reduce
or adversely change plant’s growth and development (Levitt, 1972)
 Adverse force or influence that tends to inhibit normal systems
from functioning (Jones, 1989)
 Any situation where the external constraints limit the rate of dry-
matter production of all or part of the vegetation below its ‘genetic
potential’ (Grime, 1979)
Therefore, most practical definition of a biological stress is an
adverse force or a condition, which inhibits the normal
functioning and well being of a biological system such as plants

4. Strain
• In response to the applied stress, an object undergoes a change in
the dimension, which is known as strain
• Strain can be elastic or plastic depending on the degree and lasting
time of stress
– Elastic strain: recoverable/reversible, temporary
– Plastic strain: non-recoverable/irreversible, permanent
According to Newton's law of motion, a force is always
accompanied by a counterforce, for an action there is always equal
and opposite reaction. Stress is the action and whereas strain is
the reaction

5. Difference Between Plant Stress and Strain
• The adverse reaction of plants to environmental
conditions that are unfavorable to growth, development
and productivity is called as plant stress
• Any environmental factor capable of inducing a
potentially injurious strain in plant
• Strain is the biological changes in plants under the
influence of plant stress

6. Stress and strain terminology
Stress: An external factor acting adversely on an organism
Strain: Any physical or chemical change produced by a stress
Elastic strain: A reversible physical or chemical change
produced by a stress
Plastic strain: An irreversible physical or chemical change
produced by a stress
Stressor/Stress factor: Any factor that causes injury or stress
stimulus
Stress response: Stress stimulus with ensuing state of adaptation

7.  Eustress: It is an activating, stimulating stress that increase the
physiological activity of a plant and thus a positive element for plant
development.
 Distress: It is a severe and a real stress that causes damage and thus has
a negative effect on the plant and its development
 Zero stress: The stress that is just insufficient to produce a plastic strain
 Stress resistance: Ability of the plant to survive under adverse
environmental condition is termed as stress resistance (adaptation,
avoidance and tolerance)
 Elastic resistance: Ability of the plant to prevent reversible or elastic
strain (physical or chemical change) when exposed to a specific stress

8. • Plastic resistance: Ability of the plant to reduce or prevent
irreversible or plastic strain
• Adaptation refers to heritable modifications in structure or function
that increase the fitness of the organism in the stressful environment. It
is also called protection. e.g. CAM plants to desert
• Acclimation refers to non-heritable physiological modifications that
occur over the life of an individual. These modifications are induced
by gradual exposure to the stress. The process of acclimation is known
as hardening
 Resistance adaptation/Plastic adaptation: Adaptation leading to
increased plastic resistance which prevent injury by a stress (Precht et
al, 1955 ) or it is a measure of tolerance of elastic strain
 Capacity adaptation/Elastic adaptation: Measure of avoidance of
elastic strain

9. Damage/Stress injury: It is the result of too high a stress which can not be
compensated
Dehydration : The loss of water from a cell. Plant cells dehydrate during
drought or water deficit
 Desiccation : The extreme form of dehydration. Denotes the process
whereby all free water is lost from the protoplasm
 Homoiohydry : Water economy strategy whereby plants strive to maintain
a high water potential under water limiting conditions Homoiohydric plants
possess drought avoidance
Poikilohydry : Water economy strategy whereby plants lack the ability to
control water loss to the environment. Poikilohydric plants must be drought
tolerant
Poikilotherms: Plants that tend to assume the temp. of their environment
i.e they must develop temp. tolerance

10. Types of Stress

11. Stress response flow chart
Preferable

12. Types of Stress/Strain Injury
Primary Stress
Primary Stress
Elastic strain
Elastic strain Secondary stress
Secondary stress
Direct plastic
strain
Direct plastic
strain
Indirect plastic
strain
Indirect plastic
strain
Elastic and plastic
strains
Elastic and plastic
strains
(1) Primary direct
injury
(1) Primary direct
injury
(2) Primary
indirect injury
(2) Primary
indirect injury
(3) Secondary
stress injury
(3) Secondary
stress injury
Primary Stress
Primary Stress
Elastic strain
Elastic strain Secondary stress
Secondary stress
Direct plastic
strain
Direct plastic
strain
Indirect plastic
strain
Indirect plastic
strain

13. Stress resistance and tolerance
Stress resistance and tolerance
STRESS RESISTANCE
(1)Stress avoidance
(excluded from tissue)
Stress tolerance
(survival of internal stress)
(2)Avoidance of
elastic strain
Tolerance of
elastic strain
(3)Avoidance of
plastic strain
(4)Tolerance of
plastic strain
(Reparability)
Four possible mechanisms of stress resistance

14. Plants respond to stress in
different ways
Avoidance
Plants avoid the injury of stress by building up
a barrier to prevent stress factors entering the
plant
– alfalfa survive dry habitats by sending down deep
root systems that penetrate the water table
– Halophytes secrete the salts out from the leaf thus
reduce salt content in the leaf

15. (A) Aeluropus lagopoides(Halophytes) plants growing in natural habitat
(B) Photograph showing secretion of ions from leaf sheath and leaf surfaces
(C) Salt crystals on the adaxial leaf surface
(D) Crystal count on leaves of A. lagopoides in NaCl stress Sanadhya (2015)
AoB PLANTS

16. Avoidance mechanisms
S.no. Primary Stress Avoidance mechanism
1 Chilling temperature None
2 Freezing temperature None
3 Heat High transpiration rate
4 Water a) Water conservation b) Rapid water absorption
5 Visible and IR radiation High reflection, transmission and absorption
6 UV radiation High reflection, transmission and absorption
7 Ionizing radiation High proportion of non-living:living mass
8 Salt Exclusion, excretion and dilution
9 SO2 Exclusion, precipitation and vaporization
10 Ion Stomatal closure
11 O3, PAN, etc None known
12 Pressure, EMF None possible

17. Escape
Plant avoid the injury of stress by regulating its
life cycle to avoid meeting with stress. This is not
the kind of resistance
– some short-lived, desert ephemeral plants germinate,
grow and flower very quickly following seasonal
rains. They thus complete their life cycle during a
period of adequate moisture and form dormant seeds
before the onset of dry season

19. Diawara (1997)
Msc Thesis, Kansas State University

20. Tolerance
• Plants adapt to the stress environment by
regulating their metabolism and repair the
damage caused by stress
– Highly salt tolerant halophytes survive salty habitat by
many strategies such as high ROS scavenging ability,
high osmotic adjustment ability, stress proteins and
so on

23. Environmental Stresses to Which Plants
may be Subjected
 High Temperature (Heat)
 Low Temperature (Chilling, Freezing)
 Water Deficits (Drought, Low water potential)
 Salinity
 Excess water (Flooding, Anoxia)
 Chemical (Heavy metals, Air Pollutants)
 Radiation (Visible, Ultraviolet)
 Pathogens
 Competition

24. Drought/water stress
Soil drought: no rain for long time and no available water in the
soil
Air drought: RH < 20% in atmosphere, transpiration>>water
absorption
If longer, soil drought occurs
Agricultural drought: Moisture in the soil is not sufficient to meet
the ET needs of the crop
Symptoms
Stunting, red color in base ， small cell and leaf area ， leaf
yellowish and abscission
Young leaves or/and reproductive organs wilt to death
Stress in plants

26. Fig. In vitro activities of key enzymes of C metabolism; Rubisco, G3PDH,
Ru5Pkin and FruBPase in well watered (open bars) and drought stressed
‐ ‐
grapevine (closed bars) in the middle of the summer in Évora, Portugal.
M. M. CHAVES et al
Ann Bot 2002,89:907-916

27. Membrane damage
Senescence, bio-membrane changes
Change in states, such as hexagonal phase and become leaked
Metabolic disorder
• Redistribution of water among organs
• Photosynthesis decreases, while respiration rises leads to
Starvation to death
Decrease in nuclear acids and proteins
• Protease activity↑ ， free amino acids↑ ， RNAase activity↑ ， RNA
hydrolysis ,DNA content falls down
Damages caused by stress

28. Pro accumulation ：
• Pro from protein hydrolysis; synthesis↑,oxidation↓
Pro function ：
• Detoxification of NH3; bound water ↑
Changes in plant hormones:
• Promoters↓ ， inhibitors↑ ， esp. ABA↑
Poisonous agents accumulation:
• NH3 and amines↑

32. Morphologically
• Increase in water absorption and transportation
• Declination of transpiration
• Developed root system and higher ratio of root to shoot
• Thick leaf , smaller leaf area and thick cuticle
• Developed bundle and veins
• smaller and more stomata
Physiologically
• Increase in ABA accumulation leads to Stomatal closure
• Rapid accumulation of Pro, glycinebetaine, dehydrin, osmotins,
ions etc. to Increase in capacity of resistance to dehydration of
cytoplasm
Mechanisms of resistance to drought

33. Selection of cultivars with high resistance to drought ， high yield
and quality
drought hardening by Seed priming special technology to control
seed water absorption and re-drying slowly
Suitable fertilizer application by application of more P and K to
plants
Chemical regents application like Soaking in 0.25% CaCl2 or
0.05%ZnSO4solution
Application of plant substance:ABA, CCC etc
Methods to increase the resistance in Agriculture

34.  Moisture injury is caused when soil space is filled with water and
without air
 flooding injury: Whole plant or part of shoot is submerged in water
Injures of flood to plant
 Flood is actual deficiency in O2
 Anything that increases soluble O2, will decrease the injury
 Anything that decreases soluble O2, will increase the injury
 Such as slowly streaming water causes less damage than static water
flood/excess water

35.  Injury in morphology and anatomy by O2 deficiency
 Growth decreases
 leaf yellowish (nutrition deficiency ）
 root darkness （ low Eh ）
 epinasty （ Eth)
 air root(IAA, Eth)
 stem hollow (tissue degradation caused by Eth ）
 Injury in metabolism by O2 deficiency
 photosynthesis decreases leads to stomatal block and inhibition of
CO2 entrance
 Anaerobic respiration increses toxicants: alcohol
acetaldehyde ， NH3 ， lactate , H2S

36.  Nutrition disorder
 absorption ↓ ， Soil N, P, K, Ca loss but H2S, Fe, Mn
↑ ， microelements poison
 Changes in plant hormones
 IAA and CTK ↓. ACC synthesis in root and release of Eth in shoot
 Mechanical damage and infection by harmful organism

37.  Resistance is different in plants
 hydrophytes>landplants ， rice>rape>barley;
O.sativa>O.japonica ， and in growth stages : seedling >other
stages
 Tolerance in tissues ： Well-developed aerenchyma
 Tolerance in metabolism ： mitochondria well develops in
anaerobic conditions, succinic acid dehydrogenase↑ ， tolerance
to ethanol ; PPP instead of EMP ， Glutamate dehydrogenase ↑
Mechanism of resistance to flood

38. Strategies of adaptation to excess water stresses in the
form of submergence or waterlogging in rice plants
Nishiuchi et al (2012)
Rice J

39. Kennedy et al (1980)
Plant cell and Environment

40. ☼ Each plant has its unique set of temperature requirement
for growth and development. There are two types of limits
of temperature-upper limit and lower limit.
☼ Except in the relatively stable climates vary depending on
the environment. Temperature may be of two kinds-
-High Temperature
-Low Temperature
Temperature stress

41. On close inspection, leaves display minute pores (right). When the temperature in the leaf rises above 1 or 2
degrees Centigrade, the pores open and gasses begin flowing from the colder region in the leaf to the warmer
region. Oxygen is thus taken inside the plant. The highest rate has been measured in the Amazon lily (below
left), at 30 liters (8 gallons) of gas an hour.
1. Pore (stoma)

42. Continuous…
• The effects of Low
Temperature
included the
following –
A.Chilling Stress
B.Freezing Stress

43. Chilling Stress
› Chilling injury refers to an injury that is caused by a
temperature drop to below 15°C but above the
freezing point
› Plasma membrane is the most common site for
chilling injury
› The consequences of this change may lead to cell
leakage or disruption and loss of cell liquid

44. Chilling affects on Plants
• Chilling injury causes several physiological
dysfunctions to the plant including-
 Disruption of the conversion of starch to sugars
 Decreased carbon dioxide exchange
 Reduction in net photosynthesis
 The destruction/degradation of chlorophyll

45. Methods to increase the resistance chilling stress
• The resistant cultivars
• Low temperature hardening
• Chemical control: ABA ,CCC ， PP330 ， Amo-1618
• Others: PK application, keep warm with artificial things

46. Freezing Stress
• It freezes at about -2°C, depriving the plant of its
source of water. It occurs by rapid freezing of cells to
a very low temperature
• Freezing injury in plants can be from two sources:
1. Freezing of soil water
2. Freezing of the fluids within the plant

47. Mechanism of freezing stress
 2 types: (intercellular and intracellular freezing)
Intercellular freezing
Freezing
Intercellular freezing occurs when temperature falls gradually
ice

48.  Intracellular Freezing often occurs when temperature falls
suddenly
 Ice results in the direct injury in cytoplasm, bio-membrane and
organelle, and damages to cell compartmentation and
metabolic disorder
 Much more serious damage is caused by Intracellular
freezing than by Intercellular freezing
 Damage of protein: Sulfhydryl group
 Damage of bio-membrane:Electric conductivity↑ ， cell
material leakage↑ ， photochemical activity and ATP
production ↓, while photoinhibition ↑
• Change in state of lipid and protein denaturation

49. • Cold-favored plants: some alga ， bacteria and fungi ， meets
heat injury at 15 － 20℃
• Temperature-mediate plant: most of crops at 35℃
• Temperature-favored plants: some alga ， bacteria 65-100℃ ，
many CAM plants>50℃
• Heat injury is a damage to the temperature-mediate plant by
high temperature above 35℃
High temperature stress and heat resistance of plants

50. Thermal image of a tomato plant (Solanum lycopersicum). The image compares a
living, transpiring leaf (top) to a dead leaf (bottom). The cooling effect of
transpiration is seen as darker colours in the living leaf compared to the dead leaf
Bakanae (2013)

52.  Indirect damage
 Starvation and respiration is much larger than
photosynthesis.
 Poisoning: Ethanol or acetaldehyde, free radicals
 deficiency of biotins: Biotins ， Vitamins
 damage of nuclear acids and proteins
 Direct damage
 Protein denaturation
 Configuration damage
 The degree in denaturation is positively related to water
content in plant tissue.
 Dry seed is able to resist 70 － 80℃
Reasons for heat injury

53.  High stability of protein under heat stress
 Lower water content
 High contents of saturated fatty acid.
 High contents of organic acid: CAM-extremely heat-resistance
having a great number of organic acid.
 Lessen or protect them from NH3 poison
 Form of heat shock proteins (HSPs or hsps): Heat shock proteins
are a newly synthesizing set of proteins that organisms ranging from
bacteria to humans respond to high temperature they protect or repair
proteins, nuclear acids and biomembrane from heat injury
Mechanism of heat resistance

54. Salt stress
 Salt stress occurs due to excess salt accumulation in the soil. As a
result, water potential of soil solution decreases and therefore
exosmosis occurs. This leads to physiological drought causing wilting
of plants
 Classification of plants: They are halophytes and glycophytes
 Halophytes: plants that grow under high salt concentrations and
further divided into two types based on extreme of tolerance
• Euhalophytes: can tolerate extreme salt stress
• Oligohalophytes: can tolerate moderate salt stress
 Glycophytes
• Glycophytes are the plants that cannot grow under high salt
concentration

57. Effect of salt stress on plant growth and yield
Delays seed germination due to the reduced activity of the
enzyme, α-amylase
Significant reduction in root emergence, root growth and root
length at emergence stage
Salt injury is more severe only at high temperature and low
humidity at vegetative stage
Salinity affects panicle initiation, spikelet formation,
fertilization and pollen grain germination at reproductive
stage
Salinity drastically declines photosynthetic process

58. Padilla et al (2014)
Cultivos Tropicales 35:62-66

59. Mechanism of salt tolerance
 Some plants are able to maintain high water potential by reducing
the transpiration rate
 Salts are accumulated in stem and older leaves in which metabolic
processes take place in a slower rate
 Na+ (sodium ion) toxicity is avoided by accumulating high amount
of K+ ions
 Accumulation of toxic ions in the vacuole but not in the cytoplasm.
 Accumulation of proline and abscissic acid which are associated
with tolerance of the plants to salt
Relative salt tolerant crops
 Tolerant crops: Cotton, sugar cane, barley
 Semi tolerant crops: Rice, maize, wheat, oats, sunflower, soybean
 Sensitive crops: Cow pea, beans, groundnut and grams

60. Halophytes that can Accumulate metals
Atriplex Halimus typically
accumulates low concentrations of Pb
and Cd, but has high biomass, making
it a viable candidate for use in
phytoextraction in arid, saline soils
(Manousaki and Kalergarakis 2009)
Environmental Research 326-32.
The halophyte Tamarix aphylla
(mangrove) tree excretes metals like Cd,
Li, Mg,and Ca onto the leaf surface from
its salt glands along with Na-Cl. Even in
soils with high concentrations of Cd(16
ppm), the concentration of Cd in
mangroves remains below toxic levels,
suggesting that excretion may play a role
in Cd tolerance.
(Hagemeyer and Waisel 1988)
Physiologia Plantarum

61. Mitigation of Salt Stress
 Seed hardening with NaCl (10 mM concentration)
 Application of gypsum @ 50% Gypsum Requirement (GR)
 Incorporation of daincha (6.25 t/ha) in soil before planting
 Foliar spray of 0.5 ppm brassinolode for increasing
photosynthetic activity
 Foliar spray of 2% DAP + 1% KCl (MOP) during critical stages
 Spray of 100 ppm salicylic acid
 Spray of 40 ppm of NAA for arresting pre-mature fall of flowers /
buds / fruits
 Extra dose of nitrogen (25%) in excess of the recommended
 Split application of N and K fertilizers
 Seed treatment + soil application + foliar spray of Pink Pigmented
Facultative
 Methnaotrops (PPFM) @ 106 as a source of cytokinins.

62. Biotic stress
Stress that occurs as a result of damage done to plants by other
living organisms, such as bacteria, viruses (although they are not
considered to be living organisms, also cause biotic stress to
plants), fungi, parasites, beneficial and harmful insects, weeds, and
cultivated or native plant
For example, browning of leaves on an oak tree caused by drought
stress may appear similar to leaf browning caused by oak wilt, a
serious vascular disease, or the browning cause by anthracnose a
fairly minor leaf disease
It is a major focus of agricultural research, due to the vast
economic losses caused by biotic stress to crops

63. Resistance and biotic stress
 Plant defenses
 Physical barriers: cuticle, thorns, cell walls
 Constitutively produced chemicals (e.g., phytoalexins) and
proteins (e.g., Ricin)
 Induced responses (Plant Defense Response)

64. How does the plant recognize and defend itself against pathogens?
• Plant disease has an underlying genetic basis
• Pathogens may be more or less potentially infectious to a host
– virulent on susceptible hosts
– avirulent on non-susceptible hosts
• Pathogens carry avirulence (avr) genes and hosts carry
resistance (R) genes
• The normal presence of both prevents pathogens from attacking
the plant
• Infection occurs when pathogen lacks avr genes or plant is
homozygous recessive for resistance genes (rr)

65. Potential damage by biotic stress
 Fungi cause more diseases in plants than any other biotic stress
factor
 Over 8,000 fungal species are known to cause plant disease
 Not many plant pathogenic viruses exist, but they are serious
enough to cause nearly as much crop damage worldwide as fungi
 Microorganisms can cause plant wilt, leaf spots, root rot, or seed
damage
 Insects can cause severe physical damage to plants, including to
the leaves, stem, bark, and flowers. Insects can also act as a vector
of viruses and bacteria from infected plants to healthy plants

66. S
tress only poses a problem to people or the
environm
ent if they are not prepared for it.
There can be steps taken by hum
ans to lessen
the effects. P
lants have the ability to adapt to
stress over tim
e. This is natures wayof taking
care of itself and keeping everything in
balance.