Unit 3: Plant Biotechnology

Basic Techniques of Plant Tissue Culture

Plant Tissue Culture is an in vitro technique of growing plant cells, tissues, or organs in a sterile, nutrient-rich liquid or gel medium (called a culture medium).

Key Principle: Totipotency

This technique is possible due to totipotency, the unique ability of a single plant cell to divide and differentiate into all the specialized cells of an entire plant.

Somatic Embryogenesis

• Definition: The process of generating an embryo from a somatic cell (a regular body cell, like from a leaf or stem), rather than from a fertilized egg (a zygote).
• Principle:
  1. An explant (a small piece of plant tissue) is placed on a sterile medium.
  2. Plant hormones (especially auxins) are added to induce the cells to de-differentiate and form a mass of undifferentiated cells called a callus.
  3. By changing the hormone levels, this callus can be induced to form a "somatic embryo," which can then grow into a complete, normal plant.
• Application: Used for mass propagation, creating millions of identical copies of a superior plant in a short time. Also used to produce disease-free plants.
• Limitations: The process can be difficult to control, may lead to genetic variations, and is not successful for all plant species.

Somatic Hybridization

This technique is used to create hybrid plants from species that cannot be crossed sexually (i.e., they are incompatible).

Steps of Somatic Hybridization:

1. Protoplast Isolation: The plant cell walls are digested away using enzymes (cellulase, pectinase). The resulting "naked" cell without a wall is called a protoplast.
2. Protoplast Fusion: Protoplasts from two different species are forced to fuse together, combining their cytoplasm and nuclei. This is often done using polyethylene glycol (PEG) or an electric shock (electrofusion).
3. Hybrid Regeneration: The fused hybrid cell is grown in tissue culture, where it regenerates a new cell wall and grows into a callus.
4. Plant Formation: The hybrid callus is then induced to grow into a new hybrid plant that has traits from both "parents."

Example: The "pomato," a hybrid of a potato and a tomato plant (though not commercially successful).

Biopesticides and Biofertilizers

These are biotechnological alternatives to chemical pesticides and fertilizers, aimed at creating a more sustainable agriculture system.

Biopesticides

• Definition: Pesticides derived from natural materials, such as animals, plants, bacteria, and certain minerals.
• Principle: They are often target-specific, meaning they kill a specific pest without harming beneficial insects. They are also biodegradable.
• Application: The most famous example is Bacillus thuringiensis (Bt), a bacterium that produces a protein (Cry toxin) that is toxic to specific insect larvae (like caterpillars) but harmless to humans and other animals.

Biofertilizers

• Definition: Preparations containing living microorganisms that, when applied to seeds, soil, or plants, promote growth by increasing the supply of primary nutrients.
• Principle: They do not add chemicals, but rather add microbes that "work" for the plant.
• Applications:
  • Nitrogen-Fixers: e.g., Rhizobium bacteria, which form nodules on legume roots and convert atmospheric N2 gas into usable ammonia.
  • Phosphate-Solubilizers: e.g., Mycorrhiza fungi, which form a symbiotic network with roots to help the plant absorb phosphorus from the soil.

Production of Transgenic Plants

A transgenic plant is a plant that has been genetically engineered to contain a gene from a different species (a GMO).

BT Cotton

• Purpose: To create a pest-resistant cotton plant.
• Gene: The cry gene from the bacterium Bacillus thuringiensis (Bt).
• Mechanism: The cry gene produces a protein (Cry toxin). When an insect pest (like the bollworm) eats the cotton plant, the toxin dissolves in its alkaline gut, paralyzing the digestive system and killing the insect.
• Impact: Dramatically reduces the need for farmers to spray chemical insecticides, saving money and protecting the environment.

Golden Rice

• Purpose: To combat Vitamin A deficiency, a major cause of blindness and death in children in developing countries.
• Gene: Two genes (one from maize, one from a soil bacterium) are inserted into the rice genome.
• Mechanism: These genes give the rice the ability to produce beta-carotene (the precursor to Vitamin A) in the edible part of the grain, giving it a characteristic yellow-orange or "golden" color.
• Impact: A "biofortified" food designed for a specific humanitarian purpose.