(a) How do plants absorb nitrogen from the environment ? Describe the mechanism of nitrate assimilation and synthesis of amino…

(a) Nitrogen Absorption and Assimilation

Plants absorb mineral nitrogen from the soil solution through root epidermal and cortical cells via active transport systems mediated by nitrate (NO₃⁻) and ammonium (NH₄⁺) transporters (NRT and AMT families).

Once absorbed, nitrate assimilation begins in the cytoplasm, where nitrate is reduced to nitrite (NO₂⁻) by the enzyme Nitrate Reductase (NR) utilizing NADH or NADPH. Nitrite is rapidly transported into plastids or chloroplasts, where Nitrite Reductase (NiR) reduces it to ammonium (NH₄⁺) using reduced ferredoxin.

Because free ammonium is toxic, it is promptly assimilated into amino acids via the Glutamine Synthetase–Glutamine:2-oxoglutarate aminotransferase (GS-GOGAT) cycle. Glutamine Synthetase fixes NH₄⁺ onto glutamate to yield glutamine. GOGAT then transfers the amide group to α-ketoglutarate (2-oxoglutarate), generating two molecules of glutamate. Transaminases subsequently transfer the amino group from glutamate to other keto-acids to synthesize the full spectrum of cellular amino acids.

(b) Strategies to Manage Citrus Decline in India

Citrus decline is a multi-factorial syndrome characterized by root decay, dieback, and productivity collapse, requiring an integrated management approach:

Integrated Nutrient Management: Correct nutritional disorders through balanced NPK application based on soil-leaf analysis, supplemented with targeted foliar sprays of zinc sulphate (0.5%), ferrous sulphate (0.4%), copper sulphate, and manganese to rectify frequent micronutrient deficiencies.

Rootstock and Planting Material: Propagate commercial scions on suitable rootstocks such as Rangpur lime (Citrus limonia, tristeza-tolerant) or Cleopatra mandarin (Citrus reshni, salinity-tolerant), using certified virus- and greening-free budwood (e.g., from ICAR-CCRI, Nagpur), and control the citrus psyllid that spreads greening (HLB).

Pathogen and Nematode Control: Manage Phytophthora root rot and gummosis through soil drenching and trunk painting with Metalaxyl-Mancozeb or Fosetyl-Al, combined with soil applications of biocontrol agents such as Trichoderma harzianum.

Water and Soil Management: Implement drip irrigation to prevent excess moisture and collar wetting, avoid water stagnation through proper drainage, and apply organic mulches to regulate soil temperature and root health.

(c) Mango Malformation

Mango malformation is a serious morphogenetic disorder classified into vegetative and floral types. Both vegetative malformation (bunchy top) and floral malformation are caused primarily by the fungus Fusarium mangiferae (earlier identified as F. subglutinans), often aggravated by the mango bud mite (Aceria mangiferae).

Symptoms of floral malformation include severe hypertrophy and shortening of the primary and secondary branches of the panicle, resulting in compact, crowded, and bunched floral heads. The axis thickens, flower buds remain green and open late, male flowers predominate over hermaphrodite flowers, and affected panicles set virtually no fruit, persisting on the tree as dry, blackened masses.

Control measures involve:

• Sanitation: Pruning malformed panicles along with 15–20 cm of healthy basal shoot tissue and burning them immediately.
• Chemical Application: Foliar spray of Planofix/NAA at 200 ppm during October–November (prior to flower bud differentiation) to suppress malformed panicle emergence.
• Fungicide and Acaricide Sprays: Application of a systemic fungicide such as Carbendazim (0.1%) at the bud-burst stage, together with a currently recommended acaricide to suppress the bud mite (benomyl is no longer permitted in India).

(d) Food-Based Dietary Approaches to Eliminate Hunger

Food-based dietary approaches are holistic, sustainable strategies that address undernutrition and micronutrient deficiencies by improving the production, availability, access, and consumption of diverse, nutrient-dense foods. These approaches encompass dietary diversification, biofortification of staple crops, nutrition-sensitive agriculture, and adherence to Food-Based Dietary Guidelines formulated by bodies like the ICMR-National Institute of Nutrition (ICMR-NIN).

These approaches eliminate hunger by addressing both chronic caloric deficits and "hidden hunger" (micronutrient deficiencies in iron, zinc, and vitamin A). By integrating biofortified crops (such as zinc-rich rice and iron-rich pearl millet) and promoting homestead production of pulses, millets, green leafy vegetables, and animal-source foods, food-based approaches enhance the bioavailable nutrient density of daily diets. This builds long-term metabolic resilience among vulnerable populations, reduces stunting and anemia, and provides a sustainable, localized pathway to achieving UN Sustainable Development Goal 2 (Zero Hunger) without perpetual reliance on synthetic supplementation.

(e) Major Constraints of Food Grain Processing in India

The food grain processing sector in India faces several structural, operational, and infrastructural bottlenecks:

High Post-Harvest Losses: Poor handling, threshing, and cleaning at the farm level cause significant post-harvest losses (NABCONS 2022 estimates ~4–6% for cereals, with older assessments up to ~10%), reducing raw material quality before processing.

Fragmented Supply Chains and Inadequate Storage: Long intermediary chains and a severe deficit of modern bulk handling facilities, hermetic silos, and climate-controlled storage lead to insect infestation, moisture absorption, and mycotoxin contamination.

Inefficiencies in Procurement and Buffer Stocking: Procurement and storage under open-air Cover and Plinth (CAP) systems by the Food Corporation of India (FCI) cause grain deterioration and delayed transit to processing units.

Technological Obsolescence: The sector is dominated by unorganized, small-scale custom mills using outdated machinery (such as traditional hullers instead of modern rubber-roll shellers), resulting in high grain breakage, low recovery rates, and poor by-product valorization (e.g., loss of rice bran oil and broken grain value chains).

High Capital Costs: Modernization is constrained by limited access to institutional credit for small processors and high power tariffs. Addressing these through cluster-based modernization under PM-FME is vital for value-addition.