Plant Biotechnology

Overexpression of Genes: One strategy is to overexpress the genes that encode for the first enzyme in a biosynthetic pathway. The first enzyme in the pathway is often the rate limiting step, and increasing its activity will increase the production of the end product. Agrobacterium-mediated induction of secondary roots: Another technique is to use Agrobacterium rhizogenes} to induce the formation of excessive secondary roots in plants that normally produce useful secondary metabolites in these roots, increasing their production and their harvesting.

Application of Callus Culture: Callus culture is widely used for plant regeneration and genetic transformation. It allows for:

• Production of genetically modified plants by introducing foreign genes into callus cells.
• Clonal propagation and regeneration of whole plants from undifferentiated cells.
• Screening for disease resistance and production of secondary metabolites.

A protoplast is a plant cell that has had its rigid cell wall completely removed by enzymatic digestion, leaving the plasma membrane intact. Protoplasts are spherical, naked plant cells capable of regeneration and fusion. They are widely used in plant genetic engineering, somatic hybridization, and tissue culture for introducing foreign DNA or combining genetic material from different species.

The plant hormones commonly used to promote growth and cell division in plant cell and tissue culture are:

• Auxins (e.g., Indole-3-acetic acid (IAA), Indole-3-butyric acid (IBA), Naphthalene acetic acid (NAA)): Promote cell elongation, root initiation, and callus formation.
• Cytokinins (e.g., Kinetin, Benzylaminopurine (BAP)): Stimulate cell division and shoot proliferation.
• The balance between auxins and cytokinins regulates differentiation and organogenesis in culture.

Explant culture is a plant tissue culture technique where a small piece of tissue (called an explant) is taken from a plant—such as a leaf, stem, root, or meristem—and cultured aseptically on a nutrient medium under controlled conditions. The explant cells divide and grow to form callus or regenerate into a whole plant depending on the culture conditions and plant growth regulators used. This technique is widely used for micropropagation, genetic transformation, and studying plant development.

Difficulty in producing interspecific and intergeneric hybrids: Interspecific (between species) and intergeneric (between genera) crosses often face barriers such as genetic incompatibility, failure of fertilization, or hybrid sterility. Differences in chromosome number, gene regulation, or reproductive mechanisms prevent successful hybrid formation naturally. Technique to obtain novel hybrids: Embryo Rescue Technique is commonly used to overcome these barriers:

• After a cross between two incompatible species or genera, the hybrid embryo is excised from the seed before it aborts.
• The embryo is cultured in vitro on a nutrient medium under sterile conditions.
• This allows the embryo to develop into a viable plant despite natural incompatibility.

This technique helps produce novel hybrids that are otherwise difficult or impossible through conventional breeding.