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SURYA CLASSES, , 1, , LECTURE NOTES BIOLOGY, , XII SCIENCE, , CHAPTER, NO:, CHAPTER, NO, : 708, , PLANT GROWTH AND, MINERAL NUTRITION, ,  Growth Hormones:, , The internal factors that influence growth, are called growth hormones or growth regulators as they, inhibit, promote or modify the growth. All phytohormones are, growth regulators, The term ‘hormone’ was coined first by Starling (1906), in animal physiology., o According to Thimann and Pincus (1948) : “Plant hormones are, organic substances produced naturally in higher plants affecting, growth or other physiological functions at a site remote from its, place of production and active in very minute (optimum) amount”., Hormones are transported through phloem parenchyma (Phillips, 1971)., , A.Growth promoters:, , a. Auxins, b. Gibberellins (GA), c. Cytokinins (CK)., , B.Growth inhibitors :, , A. Auxins, , a. Ethylene, b. Abscissic acid (ABA)., , [Auxien = to grow]:, [F.W.Wentin1931,used this term first], o Isolation: Auxin was isolated from urine of a person suffering, from Pellagra (Kogl and H. Smit 1931)., o Synthesis: Growing tips of root and shoot, young leaf , primordial, cells or meristematic regions of plants, o Natural auxin: - Indole-3-acetic acid (IAA) :, Tryptophan and zinc, is the primary precursor of IAA in plants. It is the first hormone to, be discovered in plants and is primarily responsible for cell, elongation. It shows polar transport - Basipetal transport in stem., 1 PLANT WATER RELATION, , | SIGN OUT BY DR. VIRESH SHELKE

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SURYA CLASSES, , LECTURE NOTES BIOLOGY, , XII SCIENCE, , o Synthetic auxins :1. IBA [Indole butric acid], 2. NAA [Naphthalene acetic acid], 3. 2, 4-D [ Dichloro Phenoxy acetic acid], , o Physiological effects and applications :, , 1. Cell elongation and enlargement :, 2. Apical dominance: Auxin inhibits the growth of axillary and, lateral buds and promotes growth of apical buds.., 3. Cell Division: Auxin stimulates growth of stem and root by, stimulating meristem cells., 4. Multiplication of cells: Auxin induces multiplication of cells,, hence used in tissue culture experiments to produce callus., 5. Formation of lateral and adventitious roots : It stimulates, formation of lateral and adventitious roots. These are marketed, as synthetic herbicides. e.g. 2, 4-D (2,4 dichlorophenoxy acetic, acid)., 6. Weedicide: It kills dicot weeds without affecting monocot crop, plants., 7. Parthenocarpy: The seedless fruits like orange, lemon, grapes,, banana etc. are produced by application of auxin (i.e. induced, parthenocarpy)., 8. Early differentiation of Xylem and phloem: Auxins promote, cell division in cambium and also cause early differentiation of, xylem and phloem., 9. Root and shoot elongation: It promotes root elongation in low, concentration and shooting at higher concentration., 10. Hastening of early rooting: It also hastens early rooting in, propagation by ‘cutting’., 11. Fruiting initiation: Foliar spray of NAA and 2,4-D induces, flowering in litchi and pineapple., 12. Prevents premature fruit drop: in apples, pear and oranges., 13. Prevents formation of abscission layer: The falling of leaves,, flowers and fruits is known as abscission. Auxin delays the rate, of abscission., 14. Increases rate of respiration: It is known to increase rate of, respiration., 15. Breaking of seed dormancy: Resting period of seed is, dormancy, 16. Promote quick germination :, 17. Pruning of plants : Auxins stimulates growth in the desired, area known as pruning, 2 PLANT WATER RELATION, , | SIGN OUT BY DR. VIRESH SHELKE

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SURYA CLASSES, , LECTURE NOTES BIOLOGY, , XII SCIENCE, , B. Gibberellins:, It is another growth promoting hormone and is, abundant in root tip and developing seeds. It shows non-polar, transport through vascular tissue., o Isolation:, Gibberellins were first isolated from the fungus, Gibberella fujikuroi by Japanese scientist Kurosawa (1926). He, observed that when rice plant was infected by fungus Gibberella, fujikuroi, it shows extensive stem elongation called ‘bakane, disease’ [foolish seedlings]., The crystalline forms of Gibberellins were isolated, by Yabuta and Sumiki (1938) from the fungus culture. They, named it as gibberellin., o Synthesis:, It is synthesized in young leaves, seeds, roots and, stem tips. These are synthesized from mevalonic acid. More than, 150 chemical types are known so far., Acetyl Co-A, Mevalonic acid, Kaurene, Gibberellic acid, o Chemical composition:, GA3 is most common and biologically, active form. Chemically it contains a gibbeane ring - a cyclic, diterpene with four isoprene units., , o Physiological effects and application :, 1. Breaking bud Dormancy: Dormancy of bud can be broken by, gibberellin treatment., 2. Breaking seed dormancy : Seed dormancy breaks with the, help of Gibberellins., 3. Promote seed germination: It can promote seed germination in, cereals like barley and wheat by synthesizing hydrolyzing, enzyme amylase which helps in hydrolysis of starch an convert it, into glucose sugar. So embryo gets maximum food material and, there is maximum germination rate., 4. Stem elongation: The most striking effect of it, is the elongation, of stem where internodes increase in length., 5. Promotes bolting: It also promotes bolting i.e. elongation of, internodes just prior to flowering in plants those with rosette, habit e.g. beet, cabbage., 6. Parthenocarpy: It causes parthenocarpy in tomato, apple and, pear, and flowering in long day plants., 3 PLANT WATER RELATION, , | SIGN OUT BY DR. VIRESH SHELKE

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SURYA CLASSES, , LECTURE NOTES BIOLOGY, , XII SCIENCE, , 7. Increases fruit size: It is used to increase the fruit size and, bunch length of grapes., 8. Conversion of Dwarf plants into tall plants: When, gibberellins are applied on genetically dwarf plants like maize,, the stem rapidly elongates and acquires the height of normal tall, varieties of maize., 9. Overcome the requirement of vernalization: Application of, gibberellins overcomes the requirement of vernalization., 10. Usually, it inhibits growth of root, delays senescence and, prevents abscission., 11. Inhibition of root growth: It also breaks dormancy of seed, and hastens germination., 12. Female sex suppression: Application of gibberellin causes, production of male flowers on female plant. [ Cucumber , Ridge, gourd, Pumpkin ], 13. Leaf expansion: External application of gibberellins helps in, leaf expansion., 14. Inducing flowers in long day plants: Gibberellins helps in, inducing flowering in long day plants., , C. Cytokinins :It is another growth hormone that promotes cell, division. Letham coined the term cytokinin., o, , Isolation :, , The first cytokinin was discovered by Skoog and, Miller (1954) during investigation of nutritional requirements of, callus tissue culture of Nicotiana tabacum (Tobacco).They, observed that the callus proliferated when the nutrient medium, was supplemented with coconut milk and degraded sample of, DNA (obtained from herring sperm)., o Chemical composition :, They named it as kinetin. Chemically, kinins are 6-furfuryl amino purine., First natural cytokinin was obtained from unripe, maize grains by Letham et al. It is known as Zeatin., 6-benzyl adenine is a synthetic cytokinin, hormone. Seven different types of cytokinins are recorded from, plants. Natural cytokinins are also reported from plants like, Banana flowers, apple and tomato fruits, coconut milk, etc., o Site of synthesis : Root apex, developing shoot , coconut milk ,, buds, young leaves and fruit, 4 PLANT WATER RELATION, , | SIGN OUT BY DR. VIRESH SHELKE

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SURYA CLASSES, , LECTURE NOTES BIOLOGY, , XII SCIENCE, , o Physiological effects and applications of cytokinin :, 1. Cell Division : Cytokinins along with auxins helps in cell division, 2. Cell enlargement: Cytokinins also promotes cell enlargement., 3. Promotes shooting / Cauliogenesis : High Cytokinins promotes, shooting. A low ratio of, Cytokinins to auxin induces root development but a high ratio, causes buds and shoots to develop., 4. Morphological differentiation: Cytokinins and auxin ratio and, their interactions control morphogenic differentiation., 5. Control apical dominance: It promotes the growth of lateral, buds and controls apical dominance by cell division., 6. Stimulates growth of lateral buds: Cytokinins stimulates, growth of lateral buds., 7. Delay in senescence [Ageing of leaves] : It delays the, senescence or ageing and abscission processes in plant organs., This was reported by Richmond and Lang (1957)., 8. Formation of interfasicular cambium: Formation of, interfasicular cambium which helps in secondary growth., 9. Cell expansion: expansion of cells is other functions., 10. Breaking seed dormancy: It also breaks dormancy and, promotes the germination of seeds., 11. Reduces rate of apical dominance: Cytokinin reverses apical, dominance effect.;, 12. RNA synthesis : It induces RNA synthesis, 13. Resistance to adverse factors :, 14. Inducing flowering in short day plant :, , D. Ethylene:, , o Isolation: It is the only gaseous growth regulator. Denny (1924), reported ethylene is effective in fruit ripening. Gane (1934), established that plants naturally synthesize ethylene., Crocker (1930) proposed that ethylene is the, plant hormone responsible for fruit ripening. It is a simple, gaseous hydrocarbon with essential role in the fruit ripening., o Synthesis: The most widely used compound as a source of, ethylene is ethephon., It is synthesized in roots, shoot apical meristem,, ripening fruits etc., , o Physiological effects and application of ethylene :, 5 PLANT WATER RELATION, , | SIGN OUT BY DR. VIRESH SHELKE

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SURYA CLASSES, , LECTURE NOTES BIOLOGY, , XII SCIENCE, , 1. Ripening of fruit: It promotes ripening of fruits like bananas,, apples and mangoes., 2. Stimulates initiation of lateral roots: It stimulates initiation of, lateral roots in plants., 3. Breaking seed dormancy: by replacing low temperature and, light requirement for germination., 4. Breaking bud dormancy: It also helps in breaking the, dormancy of bud., 5. Formation of abscission layer/separation layer : It, accelerates the abscission activity in leaves, flowers and fruits by, forming of abscission layer., 6. Apical dominance: Ethylene inhibits the growth of lateral buds, and causes apical dominance and retards flowering., 7. Promotes Senescence in leaves and flowers: It is associated, with the enhancement of process of senescence of plants organs., 8. Inducing flowering: It inhibits flowering in most of the plants, except pineapple., 9. Epinasty o leaves and flowers: It causes epinasty (drooping) of, leaves and flowers., 10. Degreening effect: It increases activity of chlorophyllase, enzyme causing degreening effect in banana and Citrus fruits., 11. Male sex suppression: Ethylene promotes male sex, suppression by increasing production of large numbers of female, flowers., 12. Formation of adventitious roots: It helps in formation of, adventitious roots., , E. Abscissic Acid, , [Stress hormone/Anti-gibberellins ] :, It is a natural growth inhibiting hormone., Carns and Addicott (1961-65) observed that the shedding of, cotton balls was due to a chemical substance abscisin I and II., , o Isolation: Wareing (1963) isolated a substance from buds of Acer, that can induce bud dormancy and named it dormin., These two identical chemical substances were given the common, name abscissic acid., o Synthesis: It is synthesized in leaves, fruits, roots, seeds etc., Chemically, it is a 15-carbon sesquiterpenoid and, synthesized from mevalonic acid., 6 PLANT WATER RELATION, , | SIGN OUT BY DR. VIRESH SHELKE

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SURYA CLASSES, , LECTURE NOTES BIOLOGY, , XII SCIENCE, , o Physiological effects and application of ABA:, , 1. Promotes abscission of leaves: It promotes abscission of, leaves, 2. Induces dormancy: It induces dormancy in many plants., 3. Bud dormancy: It controls the dormancy in buds and seeds by, inhibiting growth processes., 4. Seed dormancy: It inhibits formation of hydrolytic enzyme, amylase so starch not converted into sugar and embryo cannot, get food., 5. Promotes senescence: It accelerates the senescence of leaves,, flowers and fruits., 6. Inhibits cell division and cell elongation: It inhibits and, delays cell division and cell elongation., 7. Suppress cambium activity: Abscissic acid suppresses, cambium activity by inhibiting mitosis in vascular cambium., 8. Closing of stomata: ABA could cause efflux of k+ ions from the, guard cells and result in closure of stomata. So, it is known as, an antitranspirant., 9. Acts as stress hormone: It acts as a stress hormone by, inducing the plant to bear the adverse environmental conditions., 10. Flowering in short day plants: It inhibits flowering in long, day plants but stimulates flowering in short day plants., , 7 PLANT WATER RELATION, , | SIGN OUT BY DR. VIRESH SHELKE