(a) What are transgenic crops? Discuss the prospects and risks involved in their cultivation. (20 marks) (b) What is biological…

(a) Transgenic Crops: Prospects and Risks

Transgenic crops are plants into whose genome one or more genes from another organism, often an unrelated species, have been stably inserted by recombinant DNA technology, using *Agrobacterium tumefaciens*-mediated transformation or particle bombardment (the gene gun). The inserted gene is expressed and inherited. They differ from cisgenic plants, which receive genes from sexually compatible species, and from genome-edited plants (SDN-1 and SDN-2), which carry no foreign DNA. The first commercial transgenic crop was the Flavr Savr tomato (1994). Worldwide, GM crops, mainly soybean, maize, cotton and canola, were grown on about 190 million hectares in 2019. In India, Bt cotton (approved in 2002) is the only GM crop in commercial cultivation.

Prospects:

1. Insect resistance: Bacillus thuringiensis Cry genes (e.g., cry1Ac, cry2Ab) protect crops against bollworms and stem borers. Bt cotton now covers over 90% of India's cotton area and initially reduced insecticide use against the American bollworm; Bt brinjal is grown in Bangladesh.
2. Herbicide tolerance: glyphosate-tolerant (cp4-epsps) soybean, maize and canola simplify weed control and allow conservation tillage (herbicide-tolerant cotton is not approved in India).
3. Virus resistance: coat-protein-mediated resistance, as in the ringspot-resistant papaya 'Rainbow' that saved Hawaii's papaya industry.
4. Nutritional quality (biofortification): Golden Rice carries psy (phytoene synthase, from maize in Golden Rice 2) and crtI (from Pantoea ananatis) to make β-carotene in the endosperm, to fight vitamin A deficiency; other examples are high-oleic soybean and low-acrylamide potato.
5. Abiotic stress tolerance: e.g., drought-tolerant HB4 wheat and soybean (Argentina) and the bacterial cold-shock protein gene cspB in maize.
6. Hybrid seed systems: the barnase–barstar system for male sterility and fertility restoration underlies GM mustard hybrid DMH-11, approved by GEAC for environmental release in 2022; the matter remains before the Supreme Court.
7. Molecular farming: production of vaccines, antibodies and enzymes in plants.

Risks and concerns:

1. Gene flow: transgenes can escape by pollen to wild or weedy relatives, e.g., to wild Brassica in mustard growing areas, or to land races in centres of diversity.
2. Resistance in pests and weeds: in India the pink bollworm (Pectinophora gossypiella) became resistant to Cry1Ac and later to Cry2Ab (from about 2008–2015), and glyphosate-resistant "superweeds" (e.g., Amaranthus palmeri) have spread in the USA. Resistance management needs refuges and gene pyramiding.
3. Secondary pests: once bollworms are controlled, sucking pests such as whitefly, jassids and mealybug can rise.
4. Non-target effects and biodiversity: possible effects on beneficial insects, soil organisms and pollinators, which must be assessed case by case; reduced crop diversity if a few events dominate.
5. Food safety: possible allergenicity or toxicity of new proteins and the use of antibiotic-resistance marker genes; these are tested before approval.
6. Socio-economic issues: high seed costs and technology fees, patents and corporate control of seed, the need to buy seed each season for hybrids, and debates over trade and labelling.

Regulation: in India, GM crops are regulated under the Rules, 1989 of the Environment (Protection) Act, 1986, through the Institutional Biosafety Committees, the Review Committee on Genetic Manipulation (RCGM) and the Genetic Engineering Appraisal Committee (GEAC). Internationally, the Cartagena Protocol on Biosafety (2003) governs the movement of living modified organisms.

(b) Biological Nitrogen Fixation and the Mechanism of Symbiotic Fixation

Biological nitrogen fixation (BNF) is the reduction of atmospheric dinitrogen (N₂) to ammonia (NH₃) by prokaryotes (diazotrophs) using the enzyme nitrogenase. It adds about 100–200 million tonnes of nitrogen a year to terrestrial ecosystems, comparable to the industrial Haber–Bosch process, but at normal temperature and pressure.

1. Free-living (non-symbiotic) fixers: aerobic Azotobacter and Beijerinckia; anaerobic Clostridium pasteurianum; photosynthetic Rhodospirillum; and cyanobacteria such as Nostoc, Anabaena and Aulosira (in rice fields).
2. Associative fixers: Azospirillum in the rhizosphere of cereals, and Gluconacetobacter diazotrophicus in sugarcane.
3. Symbiotic fixers: rhizobia in legume nodules, Frankia in non-legumes, and cyanobacteria in Azolla, Cycas and Gunnera.

Mechanism of symbiotic nitrogen fixation (legume–rhizobium):

1. Recognition and signalling: legume roots release flavonoids (e.g., luteolin in alfalfa), which bind the bacterial NodD protein and switch on the ***nod* genes. The bacteria then make Nod factors** (lipochito-oligosaccharides), whose side-groups decide host specificity. Host receptor kinases (NFR1/NFR5 in Lotus) perceive them.
2. Infection: the root hair curls round the attached bacteria ("shepherd's crook"); the cell wall is dissolved locally, and an infection thread, a tube of host plasma membrane and wall, carries the dividing bacteria into the cortex. (In groundnut, bacteria enter through cracks where lateral roots emerge.)
3. Nodule formation: cytokinin signalling makes inner cortical cells divide and form the nodule primordium. Nodules are indeterminate, with a persistent meristem (pea, alfalfa, clover), or determinate and spherical (soybean, Phaseolus).
4. Bacteroid formation: bacteria are released from the infection thread into the host cytoplasm, enclosed in a plant-derived peribacteroid (symbiosome) membrane, and differentiate into nitrogen-fixing bacteroids. The plant supplies them with dicarboxylic acids (malate, succinate) as fuel.
5. Nitrogenase action: the enzyme, coded by ***nif* genes, has two parts: the Fe protein** (dinitrogenase reductase, nifH) and the MoFe protein (dinitrogenase, nifDK, with the FeMo cofactor), where N₂ binds. Electrons from ferredoxin or flavodoxin pass through the Fe protein, with ATP hydrolysis, to the MoFe protein: N₂ + 8H⁺ + 8e⁻ + 16 ATP → 2NH₃ + H₂ + 16 ADP + 16 Pᵢ The H₂ produced is partly recycled by an uptake hydrogenase (Hup).
6. Oxygen protection: nitrogenase is irreversibly damaged by O₂, yet bacteroids need O₂ for respiration to make ATP. Leghaemoglobin, whose haem is made by the bacterium and globin by the plant (which is why nodules are pink), binds O₂ and delivers it at a low, steady concentration. An oxygen-diffusion barrier in the nodule cortex also helps.
7. Assimilation and transport: NH₃ (as NH₄⁺) is exported to the plant cytosol and assimilated by glutamine synthetase–glutamate synthase (GS–GOGAT). It is then exported in the xylem as amides (asparagine, glutamine) in temperate legumes such as pea, or as ureides (allantoin, allantoic acid) in tropical legumes such as soybean.

Examples:

• Rhizobium leguminosarum bv. viciae with pea (Pisum sativum).
• Sinorhizobium meliloti with alfalfa (Medicago sativa).
• Bradyrhizobium japonicum with soybean (Glycine max).
• Bradyrhizobium and Rhizobium species with pigeon pea (Cajanus cajan) and groundnut.
• Mesorhizobium ciceri with chickpea.
• Azorhizobium caulinodans, which forms stem nodules on Sesbania rostrata.
• Frankia (an actinomycete) with Casuarina and Alnus (actinorhizal plants).
• Anabaena azollae in the leaf cavities of the water fern Azolla, used as a biofertiliser in rice.
• Nostoc in the coralloid roots of Cycas. A good legume crop fixes about 50–200 kg N per hectare per season, benefiting following crops in rotation.

(c) Forest Types of India and Their Ecosystem Services

Champion and Seth (1968) classified Indian forests into 16 type groups and about 200 types, based on climate (rainfall, temperature), altitude and edaphic factors. The major groups are:

1. Tropical wet evergreen: rainfall over 250 cm, tall multi-storeyed forests with lianas and epiphytes, found in the Western Ghats, the North-East and the Andaman Islands (Dipterocarpus, Hopea, Mesua).
2. Tropical semi-evergreen: a transition to deciduous forests, in the same regions.
3. Tropical moist deciduous: rainfall 100–200 cm, in the Himalayan foothills, the eastern plateau and the Western Ghats slopes; dominated by sal (Shorea robusta) and teak.
4. Littoral and swamp forests: mangroves (Rhizophora, Avicennia, Heritiera fomes), as in the Sundarbans, Bhitarkanika and the Andamans.
5. Tropical dry deciduous: rainfall 70–100 cm, the most extensive type, found in central India and the Deccan (teak, Terminalia, Anogeissus).
6. Tropical thorn: rainfall under 70 cm, in Rajasthan, Gujarat and the Deccan rain shadow (Acacia, Prosopis, Ziziphus, Capparis).
7. Tropical dry evergreen: found on the Tamil Nadu coast (Manilkara, Memecylon).
8. **Subtropical broad-leaved hill, subtropical pine (chir pine, Pinus roxburghii) and subtropical dry evergreen forests:** found at 1,000–2,000 m.
9. Montane wet temperate: includes the sholas of the Nilgiris and Anamalais and the oak–laurel forests of the eastern Himalaya.
10. Himalayan moist and dry temperate: oaks, deodar (Cedrus deodara), blue pine and fir–spruce, at about 1,500–3,000 m.
11. Sub-alpine and alpine: birch (Betula utilis), rhododendron and juniper scrub, and alpine meadows above about 3,500 m.

India's forest cover is about 21.8% of its geographical area, and forest and tree cover together about 25%, with a forest carbon stock of about 7,285 million tonnes (India State of Forest Report 2023).

Ecosystem services (Millennium Ecosystem Assessment categories):

1. Provisioning services: timber, bamboo, fuelwood (a major rural energy source), fodder, and non-timber forest products (tendu leaves, sal seeds, lac, honey, gums, resins, medicinal plants), which support the livelihoods of forest-dwelling and tribal communities; forests are also genetic resources for crop wild relatives, such as wild rice, mango, citrus, banana and pepper in the North-East and the Western Ghats.
2. Regulating services:

• Climate regulation and carbon sequestration: forests are central to India's NDC target of an additional carbon sink of 2.5–3 billion tonnes of CO₂ equivalent by 2030.
• Water regulation: Himalayan and Western Ghats forests feed perennial rivers, increase infiltration and groundwater recharge, moderate floods and maintain dry-season flows.
• Soil conservation: forests control erosion and landslides, and reduce siltation of reservoirs.
• Coastal protection: mangroves buffer cyclones and storm surges, as seen in Odisha in 1999 and in the Sundarbans, and act as fish nurseries.
• Pollination and pest control: forests supply pollinators and natural enemies to nearby farms.
• Local climate: forests moderate microclimate and recycle rainfall through transpiration.

3. Supporting services: soil formation, nutrient cycling, primary production, and habitat for biodiversity. India's forests harbour parts of four biodiversity hotspots, including tiger, elephant and many endemic plants.
4. Cultural services: sacred groves (devrai, kavu, sarna), ecotourism, recreation, spiritual and aesthetic values, and traditional knowledge.

These services are threatened by deforestation, degradation, fire, invasive species (Lantana, Prosopis juliflora) and climate change. They are protected through the Forest (Conservation) Act, 1980 (amended 2023), the National Forest Policy, 1988, the Forest Rights Act, 2006, CAMPA, and the Green India Mission.