What is Plant Stress ?
Stress in biology is any change in
environmental conditions that might reduce
or adversely change a plant’s growth or
development.
Stress Physiology
Resistance : resistance is the ability adaptive or tolerant to
stresses.
Resistance includes adaptation, avoidance and tolerance
Adaptation is permanent resistance to stress in morphology and
structure , physiology and biochemistry under long-term stress
condition.
a well-developed aerenchyma in hydrophytes,
a pattern for stomata movement in CAM plant.
Tolerance is a resistant reaction to reduce or repair injury with
morphology , structure, physiology, biochemistry or molecular
biology, when plant counters with stresses.
Biotic stress◇ pathogen microbe
insectsAllelopathy
Abiotic stress◇ chilling stress ◇ freezing stress◇ heat stress◇ wet stress ◇ flood stress◇ drought stress ◇ salt stress
temperatures stress
water stress
❤Biotic and abiotic stresses can reduce average
productivity by 65%~87%
Crop Record
yield
Average
yield
Average losses Abiotic losses
(% of record
yield)
Biotic Abiotic
Corn 19300 4600 1952 12700 65.8
Wheat 14500 1880 726 11900 82.1
Soybean 7390 1610 666 5120 69.3
Sorghum 20100 2830 1051 16200 80.6
Oat 10600 1720 924 7960 75.1
Barley 11400 2050 765 8590 75.4
Potato 94100 28300 17775 50900 54.1
Sugar beet 121000 42600 17100 61300 50.7
Temperature stresses (high and low temperature)
are the major environmental factors affecting
plant growth, development and also induce
morphological, physiological and biochemical
changes in plants.
Effects of high temperature stress on plants
It induces the changes in water relations (accumulation of
compatible osmolytes, decrease in photosynthesis,
hormonal changes and cell membrane thermostability
High temperatures stress (< 40"C) can cause :
- scorching of leaves and twigs,
- sunburns on leaves,
- branches and stems,
- leaf senescence and abscission,
- shoot and root growth inhibition,
- fruit discoloration and damage and reduced yield in
plants
Formation of ROS is related to ethylene
production and lipid peroxidation and
results in membrane fluidity. Ethylene
overproduction has also been found during
or after recovery from water stress.
Leaf senescence and abscission
Heat Stress
Berries are pink to bronze where directly exposed to
sun
Berries have a pleasant, wine smell
Occurs in extreme heat at/near harvest
-Environmental stresses in plants have been
associated with production of activated forms of
oxygen , including hydrogen peroxide (H2O2),
singlet oxygen, superoxide, and the hydroxyl
radical . Through a variety of reactions, O2*-leads
to the formation of H2O2, OH* and other ROS.
- Reactive oxygen species (ROS) are produced
continuously as by products of different metabolic
pathways which are located in different cellular
compartments such as chloroplast, mitochondria
and peroxisomes.
HEAT TEMPERATURE STRESS
- The ROS comprising O2*-, H2O2, 1O
2, HO2*-, OH*,
ROOH, ROO+ and RO+ are highly reactive and toxic
and causes damage to proteins, lipids, carbohydrates
and DNA which ultimately results in cell death.
Accumulation of ROS as a result of high temperature
stress is a major cause of loss of crop productivity
worldwide.
HEAT TEMPERATURE STRESS
-induces the rapid production and accumulation of reactive
oxygen species (ROS) (Mittler, 2002 Xu et al. 2008).
- These high levels of ROS are harmful to all cellular compounds
and negatively influence cellular metabolic processes
(Breusegem et al., 2001).
- The detoxification of these ROS is very important and plants
have evolved complex strategies to deal with them (Asthir et al.,
2009).
High temperature stress in Sugarcane causes a severe
reduction :
- in the first internode length resulting in premature
death of plants.
- exhibited smaller internodes,
- early senescence,
- and reduced total biomass
The plant life cycle both vegetative and reproductive phases
are affected by the low temperature stress (Nishiyama, 1995).
During reproductive development low temperature stress :
- induces flower abscission,
- pollen sterility,
- pollen tube distortion,
- ovule abortion and reduced fruit set, which ultimately
lowers yield.
During the reproductive phase cold stress has important
economic and social consequences because the reproductive
phase products are the key components of economic yield and
are the principle source of food for entire humanity (Thakur et
al, 2010).
LOW/COLD TEMPERATURE
The reproductive phase begins with transformation of the
meristem into inflorescence and flower and, in annuals, ends
upon seed reaching maturity.
The reproductive phase consists of :
- flower initiation,
- differentiation of male and female floral parts,
- micro- and mega-sporogenesis,
- development of male and female gametophytes
(pollen grain and embryo sac),
- pollination,
- micro- and mega-gametogenesis,
- fertilization and seed development.
All these stages respond differently to cold stress but
collectively all responses are negative and reduce net yield.
Intercellular crystallization
Ice crystals form between cells.
Intracellular crystallization
Ice crystals form in the cell.
Freezing Injury:
Direct injury: injury by crystal formation
Indirect injury: dehydration, suffocating
Injury mechanism:
Membrane injury
Mechanical injury
-SH theory
Strategies of increasing plant freezing tolerance:
Lower water content
Reduce photosynthesis
Increase ABA/GB
Dormant
Increase osmolytes
Caused by low temp. > 0℃
Damage
Membrane phase
Root water absorption ability
Dysfunction of respiration, accumulation of
ethanol.
Dysfunction of metabolism
Mechanism of chilling injury: membrane phase
transition:
LC phase→→G phase
LC : Liquid crystalline phase
G Phase : Gel phase
Liquid crystalline phase. The typical phase in biological membranes. The lipids have
both lateral and kinetic motion and contain membrane proteins
Gel phase. The membrane lipids have less kinetic energy and lateral motion than in
the liquid crystalline phase resulting in a regular spacing between the acyl tails
Strategies of improving plant chilling
tolerance:
Increase IUFA (index of unsaturated fatty acid),
which leads to the decrease of phase transition
temp.
Synthesis of chilling-tolerant isoenzymes.