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

(a) Economic Botany of Fibre and Gum Yielding Plants Fibre plants:

• Cotton (Gossypium hirsutum, G. arboreum; Malvaceae): fibre is the seed hair (unicellular trichome) of the seed, nearly pure cellulose. Used for textiles, yarn, cloth, surgical cotton and cottonseed oil. India is a leading producer.
• Jute (Corchorus capsularis, C. olitorius; Malvaceae): bast (secondary phloem) fibre from the stem, retted in water. The "golden fibre" for gunny bags, hessian, ropes and carpets, grown chiefly in West Bengal.
• Flax (Linum usitatissimum; Linaceae): bast fibre from the stem, used for linen cloth, and seeds give linseed oil.
• Coir (Cocos nucifera; Arecaceae): mesocarp (husk) fibre of the fruit, used for ropes, mats, brushes and mattresses, especially in Kerala.
• Sisal (Agave sisalana; Asparagaceae): leaf fibre (vascular bundle fibres), used for ropes, twine and rugs.

Gum yielding plants:

• Gum arabic, from Acacia senegal (Fabaceae): exudate from bark incisions; used in confectionery, pharmaceuticals, inks, adhesives and as an emulsifier.
• Gum karaya, from Sterculia urens (Malvaceae): exudate from tapped bark, an important Indian forest product used as a laxative, denture adhesive and food stabiliser.
• Gum tragacanth, from Astragalus gummifer (Fabaceae): exudate from stems, used in pharmaceuticals, cosmetics and textiles.
• Guar gum, from Cyamopsis tetragonoloba (Fabaceae): galactomannan from the endosperm of seeds (mucilage, not exudate), used in food, paper, textile and oilfield drilling; Rajasthan is the main producer.
• Gum ghatti, from Anogeissus latifolia (Combretaceae): exudate, used as an emulsifier and binder.

(b) Factors Affecting Somatic Embryogenesis Somatic embryogenesis is the formation of embryos from somatic cells without fertilisation, as first shown in carrot (Steward, Reinert, 1958-59).

• Plant growth regulators: an auxin, mostly 2,4-D, induces embryogenic callus. Embryo development needs lowering or removing the auxin, with cytokinin or ABA, and the auxin-cytokinin balance is crucial.
• Genotype and explant: embryogenic competence varies between species and cultivars (carrot, Medicago, citrus, cereals), and explants such as immature zygotic embryos, young leaves and hypocotyls respond best, because juvenile, actively dividing tissue is more competent.
• Medium: basal media (MS, B5, N6) with a reduced nitrogen source (ammonium, glutamine, casein hydrolysate), sucrose of 2-3% (higher osmotic levels help maturation), and pH about 5.8; polyamines and activated charcoal help.
• Physical conditions: dark for induction, temperature about 25 ± 2°C, and light for maturation; cell density and subculture influence response.
• Stress: osmotic stress, heavy metals, heat shock and wounding can trigger embryogenesis.
• Genes: SERK, LEC1, LEC2, BBM, WUS and AGL15 regulate embryogenic competence.

Confusion with zygotic embryogenesis should be avoided: somatic embryos arise without gamete fusion, and their quality is judged by conversion to plants.

(c) Isolation of Protoplasts from Leaf Tissue Protoplasts are cells with the cell wall removed. A standard method with tobacco leaves is:

1. Select healthy, fully expanded young leaves from 4-6 week-old plants. Surface sterilise (70% ethanol, then dilute sodium hypochlorite), rinse with sterile water, and peel the lower epidermis or cut leaves into fine strips.
2. Plasmolyse in a solution with an osmotic stabiliser (0.4-0.6 M mannitol or sorbitol) to protect protoplasts from bursting.
3. Incubate in an enzyme mixture (cellulase, about 1-2%, with macerozyme or pectinase, about 0.1-0.5%, in mannitol solution with CaCl₂, pH about 5.6) in the dark at about 25-28°C for several hours (3-16 hours), with gentle shaking.
4. Filter through nylon mesh (about 60-100 μm) to remove undigested tissue.
5. Centrifuge gently (about 100 g for 5-10 minutes), then wash the pellet 2-3 times with osmoticum; purify by floating on a sucrose cushion (about 21%).
6. Check viability with fluorescein diacetate (green fluorescence in living cells) or Evans blue, count with a haemocytometer, and culture in a suitable osmotic medium, where cell walls regenerate and division follows.

Uses: protoplast fusion for somatic hybrids, transformation and cybrids.