Abiotic stress Cont…. & Role of Tissue Culture (Lecture 26)
Wind Stress:
About 50% of crop yield in Pakistan is effected by the wind stress. Due to following reasons:
qStorm & high pressure winds cause
- the falling of flowers which decrease the crop yield.
- Increase transpiration rate.
- Hot wind also have retarding growth effects on plants.
- Wounds or wilting caused by winds give sites for the virus or bacterial infections.
Heavy Metal Stress:
Cu, Zn, Ni, Co, Cs, Hg, Cr, etc.
- Essentials heavy metals: Required for all kinds of plants.
Cu – Photosynthesis
- Beneficial heavy metals: Required for specific plant groups.
Ni – Activation of Enzymes
- Non-Essentials heavy metals: Not required & accumulated in plant body due to the weak uptake control mechanism.
Example: Cd, Hg, Cr etc.
- Source of entrance: In terrestrial system metals ions enter in the plant through root hairs & in aquatic system through foliage either cracks on the cuticle or stomata plasmalemma.
- Stress caused by heavy metals: Elevated concentration of both essentials & non-essentials heavy metals in the soil can lead to the toxicity symptoms to the plant growth. It can also disturb the photosynthetic system.
Oxidative stress (ROS):
-Abiotic/biotic stresses accelerates the generation of ROS including singlet oxygen (1O2), superoxide radical (O2•–), hydrogen peroxide (H2O2) and hydroxyl radical (OH•), thereby induced oxidative stress.
-In plant cells, ROS are continuously produced, particularly in the chloroplast, mitochondria and peroxisomes. But the chloroplast is considered as the main source of ROS in plants.
-The main effects of ROS include autocatalytic peroxidation of membrane lipids and pigments, modification of membrane permeability and functions.
-During the time of stress, ROS level can increase dramatically which can result in significant damage to cell structure.
Antioxidant production:
-Abiotic stress – drought, salt, chill- increases reactive Oxygen species (ROS) in plants
-ROS- stress signal- due to altered metabolic functions of chloroplast, mitochondria
ROS SCAVENGING
Antioxidant system contains a battery of enzymes that scavenge ROS- Superoxide dismutase (SOD), peroxidases, catalases, glutathione reductases
Antioxidant defense under Abiotic stresses:
Plants have various enzymatic and non-enzymatic defense systems to minimize the deleterious effects of ROS which include :
q
*Enzymatic defense systems : catalase (CAT), ascorbate peroxidase (APX), monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR), glutathione reductase (GR), glutathione S-transferase (GST), glutathione peroxidase (GPX), superoxide dismutase (SOD) etc.
*Non-enzymatic compounds: such as ascorbate (AsA), glutathione (GSH), carotenoids etc.
-However, under the extreme condition, ROS production overwhelm the scavenging action of the antioxidant system, which results in extensive cellular damage and death.
-In such cases external protectants as well as genetic manipulation of defense genes can work in upregulating the defense system.
-There are numerous plant studies which indicate the tolerance to abiotic stresses in plants is positively correlated with an increase in antioxidants
Role of Tissue Culture:
- Plant tissue culture is much benefited in terms of that to introduce the resistance or tolerance in plants against all the biotic & A-biotic stresses.
2. It remarkably plays an important role in increased yield of crops, better and rapid growth, flowering & efficiency of plant’s internal homeostasis.
3. Transgenic plants are produced by the genetic engineering techniques.
4. Genetic transfer of genes involves the removal of gene from one species and inserting them into another species. This does not require sexual incompatibility.
5. The new DNA remains stable & can transmit the transfer gene to offspring, resulting in development in transgenic plant.
Techniques of gene transfer:
- Agro bacterium mediated gene transfer
2. Electroporation
3. Microinjection
4. Particle bombardment technology
5. Gene gun method
Agro bacterium mediated gene transfer:
Ø Agro bacterium is a gram negative bacterium commonly occurring in soil (causing crown gall disease).
Ø It contain plasmid DNA vector which can carry any DNA sequence.
Ø By placing foreign gene into T-DNA region of the plasmid, cloning of the introduced gene is possible.
Electroporation:
Ø electropermeabilization, is a molecular biology technique in which an electrical field is applied to cells in order to increase the permeability of the cell membrane, allowing chemicals, drugs, or DNA to be introduced into the cell.
Ø method of introducing recombinant DNA into eukaryotic cell is electroporation, applying a brief electrical pulse to create temporary holes in the cell membranes.
Ø Alternatively, scientist can inject DNA into cells using microscopically thin needles.
Particle bombardment technology:
1.This technology can work with all type of plants.
2.DNA is carried on microscopic metal particles.
3.Fired by a gene gun into the plant tissue.
Gene Gun Method:
This device injects cells with genetic information using a heavy metal element-bullet coated with plasmid DNA.
This device can be used on almost any cell and it isn’t limited to transforming genetic information in the nucleus. It also can modify other organelles.
Approved Transgenic plants…..
- Soybean
- Corn
- Cotton
- Sugarbeet
- Squash
- Tomato
- Tobacco
- Carnations
- Potato
- Flax
- Papaya
- Rice
- Melon