Plant Physiology & Agriculture

• Plant Physiology: Study of the interrelationship of cells, tissues, and organs in plants.
• Stephan Hales: Known as the Father of Crop Physiology.

The Role of Plant Physiology in Agriculture

• Mineral Nutrition: Essential for nutrient uptake and growth, also aids in detecting nutrient deficiencies or toxicities.
• Khaira disease in paddy is controlled by applying Zinc (Zn).
• Photoperiodism involves controlling flowering through the duration of light exposure.
• Vernalization involves controlling flowering through temperature changes.
• Increasing yield capacity depends on the production of assimilates, storage ability, and efficient translocation of solutes.
• Higher translocation capacity leads to more food stored in seeds, resulting in a higher yield.
• C3 plants are less efficient than C4 plants due to photorespiration.
• Reducing photorespiration increases photosynthetic efficiency in C3 plants.

Growth Regulators & Their Roles

• Synthetic Auxins prevent premature fruit drop, are used in parthenocarpy (seedless fruit production), and act as selective weedicides.
• Gibberellins (GA) increase stalk length, break seed dormancy, increase sugar content in sugarcane, and activate alpha-amylase enzyme in barley.
• Cytokinins promote cell division, delay aging (senescence) in leaves, and are used for tissue culture and shoot formation.
• Cycocel (CCC) controls plant height and prevents lodging.
• Maleic Hydrazide (MH) prevents premature sprouting in storage.
• Ethephon induces flowering in pineapple and ripens sugarcane.

Physiological Breeding

• Involves selecting genotypes based on physiological traits.
• IR-8 rice variety was developed through physiological breeding.
• Donald’s Ideotype Concept helps in developing plants that perform well under water stress.

Seed Dormancy & Flowering Promotion

• Gibberellins (GA), Cytokinins, and Ethylene break seed dormancy.
• Auxins, Gibberellins, and Ethephon stimulate flowering.
• Ethephon increases the number of female flowers in cucumber & pumpkin.

Weed Control in Agriculture

• Auxin-based herbicides include 2,4-D (2,4-dichlorophenoxyacetic acid), 2,4,5-T (2,4,5-trichlorophenoxyacetic acid), and MCPA (2-methyl-4-chlorophenoxyacetic acid).
• Pre-emergent herbicides: Atrazine, Pendimethalin, Butachlor, Thiobencarb.
• Post-emergent herbicides: Paraquat, Glyphosate, 2,4-D.
• Paraquat is a contact herbicide.

Important Scientists & Their Contributions

• Robert Hooke (1665) coined the term cell.
• Anton van Leeuwenhoek observed microorganisms.
• Dixon & Jolly (1894) proposed the Cohesion-Tension Theory for water movement in xylem.
• Buchner (1897) discovered enzymes.
• Neljubow (1901) discovered the Ethylene triple response.
• Blackman (1905) discovered the dark reaction in photosynthesis and the Law of Limiting Factors.
• Funk (1912) introduced the term vitamin.
• Garner & Allard (1920) discovered photoperiodism in plants.
• Kurosawa (1926) discovered Gibberellins.
• Arnon & Stout (1939) discovered essential elements for plant nutrition.
• Watson & Crick (1953) discovered DNA structure.
• Calvin (1954) discovered the Calvin Cycle (C3 Cycle).
• Miller & Skoog (1955) discovered Cytokinins.
• Hatch & Slack (1966) discovered the C4 Pathway (Hatch-Slack Cycle).
• Addicott (1967) discovered Abscisic Acid (ABA).