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Uploaded byVasantaKahalkar
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Growth regulator & auxin

This document discusses plant growth regulators, specifically auxins. It defines growth and categorizes growth-controlling substances into growth promoters and inhibitors. Auxins are described as growth-promoting substances that were first discovered through experiments showing they promote growth in coleoptiles and cause curvature. The role of auxins is summarized, noting they promote stem elongation, root growth, apical dominance, fruit development, and tropic movements in plants. Auxins are widely used to enhance growth, induce rooting, delay abscission, and produce parthenocarpic and seedless fruits in agriculture.

Education◦
Plant growth Regulator Dr. Vasanta I. Kahalkar Department of Botany M. G. College, Armori
Plant growth Regulator Definition :- Growth is a permanent & irreversible increase in the number and size of a cell, organ or whole organism ,related to change in size & mass . • Based on the function these growth controlling substance are categorized into two types. • A) Growth Promoters- the substance that enhance or promote growth. Ex.- Auxin, Gibberellins and Cytokinnin. • B) Growth inhibitors- The substance that inhibit or stop growth of plant organ. So they are called growth inhibitors or growth reardants. Example- Abscisic acid, Ethylene.
Auxins • Auxins are promoting substance which promotes growth of coleoptile, seedlings, mature plant and plant organs. • Charls Darwins (1880) for the 1st time proved in Canary grass that plant parts movement is related to light induced and gravitational force. Boysen & Jensen (1913) suspected that a substance produced in the coleoptile of grasses promoting growth and curvature towards light. F. W. went (1928) extracted the growth promoting substance and identified it as auxin. The term Auxin was coined later by F. Kogl (1934).
• Went proved the plant movement by two experiments on Oats (Avena sativa) plant Avena growth curvature test. • (1) Avena growth test :- Coleoptile (seedling stem tip) of Avena seedling was cut and it was placed on a Agar block. Now the growth promoting substance is transferred to agar block. Then he kept the agar block on decapitated Avena seedling. It result in the increase in height of the plant. When the agar block was treated with coleoptile tip, there was no growth.
• Avena curvature test :- the agar block was treated with coleoptile tip(like in Avena growth test) but now he kept the cut part of coleoptile aside (just away from center). The growth promoting substance travelled from agar block to into decapitated coleoptile partially and laterally. This has resulted in curved growth on the opposite side. • As e accumulated on one side the cells exhibited more cell division and more growth occurred on that side. So, the plant showed curvature. • Both the above experiment prove that the growth promoting substance is synthesized naturally in the shoot apex region and move downward to initiated and promote cell division.
Role of Auxin • Auxin show various physiological activities in plant, besides apical growth of shoot and root. It promotes some activities while inhibits some other. • 1. Stem height is increased by cell division and cell elongation and its promoted by auxins by decreasing wall pressure and increasing the size of vacuole. Auxine also promote secondary growth and formation of annual rings. • Low concentration of auxins promote root growth, but high concentration inhibit the same. Auxin stimulate formation of adventitious root from stem cutting. Synthetic auxins like NAA ( Naphthalene Acetic Acid), IBA (Indole Butyric Acid) are effectively used in vegetative propagation of ornamental plants. • Auxins promote apical dominance by supporting growth of lateral buds. So, NAA & IBA are used in the storage of potato tubers. (potato tubers contain numerous lateral buds called eyes.) • Auxins do not promote flowering, but in Pineapple NAA observed to promote flowering.
• Auxins promote femaleness in Cucurbits. They increase the number of female flowers. • Development of unpollinated carpel into a fruit is called Parthenocarpy. Parthenocarpic fruit are seedless. Synthetic auxins like NAA & PCPA (para-chlorophenoxy acetic acid) are successfully used to produced seedless varieties in citrus, pineapple, orange and tomato. • Abscission means shedding of plant organs like leaves, flowers & fruit. It is caused by the formation of abscission layer between stem and that particular organs. This can be delayed by spraying auxins. NAA prevents premature fruit fall in Apple. • Auxins are responsible for ‘tropic movements’ in plants. The movement of plant organ in response to external stimuli is called ‘Tropic movement’. Movement in response to gravity is ‘Gravitropism ‘, and in response to light is ‘photoropism’ . Roots show positive gravitropism (geotropism), and negative phototropism, while stem show positive phototropism and negative geotropism.
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