(a) Describe the economic botany of fibre and gum yielding plants (five species each). (20 marks) (b) Discuss the factors…

Economic Botany of Fibre and Gum Plants

Fibre and gum yielding plants constitute vital sectors of economic botany, providing raw materials for textiles, packaging, and industrial applications.

Fibre Yields Five major fibre plants are:

1. **Cotton (Gossypium hirsutum):** Source of lint (seed fibre). Extraction involves ginning to separate fibres from seeds. Used in textiles, cottonseed oil, and paper.
2. **Jute (Corchorus capsularis):** Bast fibre from the stem. Extraction via retting (water or enzyme) and decortication. Used in sacks, geotextiles, and biodegradable packaging.
3. **Flax (Linum usitatissimum):** Bast fibre. Retting and scutching yield linen. Used in high-quality textiles, rope, and paper.
4. **Hemp (Cannabis sativa):** Bast fibre. Similar extraction to jute. Used in industrial textiles, rope, and construction materials.
5. **Sisal (Agave sisalana):** Leaf fibre. Mechanical decortication of leaves. Used in cordage, mats, and brush bristles.

Gum Yields Five major gum plants are:

1. Acacia senegal (Gum Arabic): Exudate from bark. Chemistry: Arabinogalactan. Tapped manually. Used in food emulsifiers, pharmaceuticals, and ink.
2. Sterculia urens (Karaya Gum): Exudate from trunk. Chemistry: Galactomannan. Tapped. Used in adhesives, explosives, and food thickener.
3. Astragalus gummifer (Tragacanth): Exudate from roots/stems. Chemistry: Rhamnogalacturonan. Harvested from dried exudates. Used in cosmetics, food stabilizer, and oil well drilling.
4. Anogeissus latifolia (Ghatti Gum): Exudate from bark. Chemistry: Polysaccharide. Tapped. Used in adhesives, paints, and pharmaceuticals.
5. Bauhinia variegata (Gum Karaya source, distinct from Sterculia): Exudate from bark. Chemistry: Polysaccharide. Tapped. Used in adhesives and food industry.

Factors Affecting Somatic Embryogenesis

Somatic embryogenesis (SE) is the in vitro formation of embryos from somatic cells. Key factors include:

Genotypic and Explant Factors Genotype determines embryogenic competence. Explant source (e.g., zygotic embryos, callus, leaf) influences the pathway. Direct SE arises from pre-embryogenic determined cells (PEDCs) without dedifferentiation. Indirect SE involves dedifferentiation into induced embryogenic determined cells (IEDCs) via callus.

Growth Regulators Auxin, particularly 2,4-D, is critical for induction. High 2,4-D promotes IEDC formation in indirect SE. Subsequent reduction or removal of auxin is often sufficient for maturation through globular, heart, torpedo, and cotyledonary stages. Cytokinins (e.g., BAP) can be inhibitory or supportive depending on the system; they are not universally obligatory for stage progression. Abscisic acid (ABA) promotes maturation and desiccation tolerance, distinct from osmotic stress inducers like PEG or high salt/sugar concentrations.

Nutritional and Physical Factors Nitrogen source affects maturation; NH4+ often promotes embryogenic competence, while NO3- supports growth. Physical factors include light (photomorphogenesis), temperature (25°C optimal), and osmotic stress (PEG) which can induce or enhance SE. Biochemical markers like SERK gene expression correlate with competence. Conversion efficiency varies by species, impacting synthetic seed technology.

Isolation of Protoplasts from Leaf Tissue

Protoplast isolation involves enzymatic removal of the cell wall.

Pre-treatment and Enzyme Cocktail Leaf segments are pre-plasmolyzed in high osmoticum (0.4–0.6 M mannitol/sorbitol) to stabilize membranes. The enzyme cocktail typically includes Cellulase Onozuka R-10, Macerozyme R-10, and Driselase (pectinase/hemicellulase).

Incubation and Filtration Tissue is incubated in the enzyme solution at 25°C for 4–16 hours under gentle agitation. The mixture is filtered through nylon mesh (e.g., 100–200 µm) to remove debris.

Purification and Viability Protoplasts are purified by floatation in sucrose gradients or washing. Viability is assessed using FDA staining (fluorescein diacetate), visualized under blue light (~490 nm excitation), or Evans blue exclusion. Yield is calculated based on cell count. Protoplasts are essential for somatic hybridization and genetic transformation.

Conclusion Systematic understanding of fibre/gum extraction, SE factors, and protoplast isolation underpins plant biotechnology applications, from industrial raw material supply to genetic engineering and synthetic seed production.