Response of plants to some biotic & abiotic stresses Flashcards
Two types of stresses:
- Abiotic Stresses (due to non-living factors)
- Biotic Stresses (due to living factors)
What are the 3 types of abiotic stresses?
- Drought stress
- Cold stress
- Salt stress
Describe drought stress
Plants may wilt when water loss by transpiration exceeds water absorption
Prolonged drought may even kill a plant
Plants have control systems that enable to cope with drought / water deficit conditions
Water deficit stimulates increased synthesis and release of ABA, which acts on guard cell membranes, closing stomata to reduce transpiration
In grasses, the leaves roll into a tube-like shape which reduces the surface area to reduce transpiration.
Some plants shed their leaves during seasonal drought
What are the adaptations displayed by plants to cope with drought conditions
Water deficit stimulates increased synthesis and release of ABA, which acts on guard cell membranes, closing stomata to reduce transpiration
In grasses, the leaves roll into a tube-like shape which reduces the surface area to reduce transpiration.
Some plants shed their leaves during seasonal drought
Describe cold stress
When cell membrane cools below a critical temperature, it looses its fluidity due to the lipids becoming locked into a crystalline structure.
This blocks the transport across the membrane and affects cell’s functions
Plants respond to cold stress by altering lipid composition of their membranes. They increase the proportion of unsaturated fatty acids which keeps the membranes more fluid at low temperature
Freezing is another cold stress.
Water in the cell wall and intercellular spaces freezes before freezing the solute-rich water in the cytosol.
The reduction of liquid water in cell wall lowers the extracellular water potential causing water in the cytosol to leave. This results high concentration of solutes in the cytoplasm which is harmful and leads to cell death
Before onset of winter, the cell of frost-tolerant plants increases cytoplasmic levels of specific solutes such as sugars to help reduce water loss from cells, preventing dehydration
Describe freezing as a cold stress
Freezing is another cold stress.
Water in the cell wall and intercellular spaces freezes before freezing the solute-rich water in the cytosol.
The reduction of liquid water in cell wall lowers the extracellular water potential causing water in the cytosol to leave. This results high concentration of solutes in the cytoplasm which is harmful and leads to cell death
Define biotic stress
Biotic stress is how plants defend themselves against pest and pathogen attacks
Describe biotic stress
- Biotic stress is how plants defend themselves against pest and pathogen attacks
- In plant defense mechanisms, some compounds and structures are already existed while others from after pest attacks.
- 2 categories of defense mechanisms can be identified as:
1. Pre-existing mechanisms
2. Induced mechanisms
Name the physical pre-existing defense mechanisms
- Amount and quality of wax and cuticle covering the epidermis
- Structure of epidermal cell walls and thickness
- Size, location, and shapes of stomata
- Thorns, pricks and trichomes
Name the chemical pre-existing defense mechanisms
Plants producing secondary metabolites
Ex: toxic compounds such as
- cyanogenic glycosides
- alkaloids such as nicotine
- phenolics such as flavonoids
- lignin and tannins
- terpenoids such as lectin and Azadirachtin
Name the physical induced defense mechanisms
- Morphological changes in the cell wall
- Formation of cork and abscission layer
Name the chemical induced defense mechanisms
- Production of phenolic compounds
- Production of toxic compounds
- Production of enzymes that can degrade cell walls or damage insect organs
