Plant Tissue Culture Applications

Plant Tissue Culture Application

• Plant tissue culture applications include suspension cultures, somatic embryogenesis, organogenesis, micropropagation, haploid production, germplasm conservation, and somaclonal variations.

Organogenesis

• Organogenesis, also called morphogenesis, is the production of new organs not previously present in an explant.
• Tissues or organs with the capacity for morphogenesis/organogenesis are morphogenic or organogenic.
• New organs, such as shoots and roots, induced on cultured plant tissues are called adventitious shoots and roots.

Summary of Pathways to Morphogenesis

• Various pathways exist for morphogenesis, including direct morphogenesis (from explant) and indirect morphogenesis (through callus).
• Methods encompass meristem culture, shoot tip culture, axillary branching, multiple axillary shoots, node culture, direct shoot formation leading to somatic seedlings and adventitious shoots, direct embryogenesis with somatic embryos, and indirect shoot/embryo formation.
• Different methods involve explants from various plant tissues, callus growth, suspension cultures, and resulting plantlets/seedlings/somatic embryos.

Somatic Embryogenesis

• Somatic embryogenesis is the process where a somatic cell differentiates into an embryo.
• Embryos formed by somatic cells are called somatic embryos.
• Somatic embryos can originate directly from explants or indirectly after callusing.

Somatic Embryos

• Somatic embryos resemble zygotic embryos morphologically.
• They are bipolar and bear typical embryonic organs.
• They are not connected to explant or callus cells by vascular tissue.
• They allow large-scale vegetative propagation, particularly through bioreactors.
• Somatic embryos can be cryopreserved for long-term storage.

Angiosperm Embryo Development

• Stages of embryo development in angiosperms (e.g., Arabidopsis) are depicted.
• Stages include initial stages such as proembryo phase, pattern formation, organ expansion, and maturation. 
• Different stages include proembryo, globular, heart, torpedo, and seed phases.

Callus and Suspension Culture

• Callus refers to a rapidly growing mass of unspecialized, unorganized cells produced when explants are cultured under appropriate conditions involving auxin and cytokinin at specific ratios.

• Callus cultures can be compact or friable; compact callus has densely grouped cells, while friable callus has loosely associated ones.

• Various different types of callus can exist such as embryogenic and non-embryogenic callus.

• Developmental stages of callus culture exist and include Induction (cell division initiates), Proliferative (rapid cell division phase), and Morphogenesis (organized structures/plant regeneration form).

• Cell suspension cultures are initiated from friable callus, in a liquid medium, and agitated.

• Suspension cultures grow faster than callus cultures.

• The media commonly includes 2,4-D and sometimes pectinase to increase the growth of single cells.

• Methods of producing and maintaining cell suspension cultures are presented.

• Growth curves of cell cultures have characteristic phases: lag phase, exponential phase, deceleration phase, stationary phase, and death phase.

Applications of Cell Suspension Culture

• Bioreactors are used for large-scale production of commercially important secondary metabolites and foreign recombinant proteins.
• Culture maintenance and monitoring procedures using bioreactors are involved.

Protoplast and Protoplast Fusion

• Protoplasts are plant cells that have their cell walls removed.
• Somatic fusion/protoplast fusion is a type of genetic modification technique where protoplasts from separate distinct plant species are fused.
• The hybrid develops and creates new characteristics of both parent plants, and regenerate a wall in a culture medium.

Haploid Production

• Haploid plants possess a single set of chromosomes (n), unlike diploid plants (2n).

• Haploid plants are crucial for producing homozygous lines, improving plant breeding, and creating important plants.

• Various methods for haploid production include androgenesis (male haploids), gynogenesis (female haploids), distant hybridization, irradiation, and chemical treatments.

• In vitro techniques like anther and microspore culture are involved in haploid production. 

Germplasm Conservation

• Methods for preserving plant genetic diversity include in situ (in natural habitats) and ex situ (e.g., gene banks, seed banks) conservation.
• In vitro methods (e.g., cryopreservation, cold storage, low-pressure and low-oxygen storage) are for preserving germplasm.

Somaclonal Variation

• Somaclonal variation describes genetic variations in plants regenerated from somatic cells in vitro.
• Somaclonal variation is useful in breeding programs of crop plants, and produces variations for use in plant varieties or breeding.
• Variations can yield advantages (e.g., improvements in crops, secondary metabolites) or disadvantages (e.g., difficulties with uniformity).