Introduction to plant stresses (Lecture 24)
Brief Introduction to Plant Stress Physiology
*Contains
◇ Types of stresses in plants
◇ Stress factors
◇ Types of resistance
◇ Adaptation vs Acclimation
◇ Stress responses
Primary stresses:
Drought, chilling, salinity, temperature, light etc
Secondary stresses (induced by primary stresses):
–Water stress induced by salinity/heat
-O2 stress induced by water logging
Adaptation versus Acclimation:
*Adaptation – are special features that allow a plant to live in a particular place or habitat.
These include
Ø modification of existing genes,
Ø gain/loss of genes.
- e.g., thermo-stable enzymes in organisms that tolerate high temperature
*Acclimation – inducible responses that enable an organism to tolerate an unfavorable or lethal change in their environment.
- e.g., heat shock response
Types of Resistance:
# Resistance ：The adaptability of plants to adverse environment
◇Stress avoidance ◇ Stress tolerance
- stress avoidance (protective)
In the whole growth process plant does not meet with the face of adversity
- stress tolerance
Plant has a capacity of environmental stress defense, and a variety of physiological processes remain normal
Plants respond to stresses as individual cells and as whole organisms – stress induced signals can be transmitted throughout the plant, making other parts more ready to withstand the stress..
Most organisms are adapted to environmental temperature:
1.Psychrophiles (< 20 °C)
2.Mesophiles (~ 20-35 °C)
3.Thermophiles ( ~35-70 °C)
4.Hyperthermophiles (70-110 °C)
Groups 1,3 & 4 are “Extremophiles”
But can also acclimate to “extreme” shifts, if they are not permanent, and not too extreme.
Two well studied acclimation responses are:
- the Heat Shock response
- Cold acclimation
Heat Stress (or Heat Shock) Response:
*Induced by temperatures ~10-15oC above normal
* Dramatic change in pattern of protein synthesis
- induction (increase) of HSPs
- most HSPs are chaperones (chaperonins) that promote protein re-folding & stability
Thermotolerant growth of soybean seedlings following a heat shock.
Cold Acclimation (CA) involves:
*Increased accumulation of small solutes
- retain water & stabilize proteins
- e.g., proline, glycine betaine, trehalose
*Altered membrane lipids, to lower gelling temp.
*Changes in gene expression [e.g., antifreeze proteins, proteases, RNA-binding proteins]
RESISTANCE:
- Depends on
1.Species
2.Genotype
3.Age of plant
4.Duration, severity, rate of stress
STRESS RESPONSE:
1.Alarm phase – stress reaction
2.Restitution- repair
3.Hardening
4.Adjustment
5.Adaptation- normalization
6.(Exhaustion)- irreversible damage
7.End phase
