Growth hormone

Growth hormone

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  Concept and Typesof Growth Hormone, Their Role in Field Crop Production and Efficient Use of Resources Presented by ; Karan Verma cskhpkv
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  Hormone  Definition: Ahormone which stimulates growth in animal or plant cells  Plant growth substances are biochemicals produced in plant (endogenous) or synthetic substances applied to plants externally (exogenous) which cause modifications in plant growth and development.  Plant growth substances produced by the plant are referred to as phytohormones.
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  Growth substances initiatebiochemical processes which help in increased production of roots, shoots, flowers etc. Plant growth substances are manily grouped into growth promoters (which enhace growth) and growth retardants (which reduced growth).
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  Types of growthhormone 1. Auxin 2. Gibberellins 3. Cytokines 4. Ethylene 5. Inhibitors 6. Growth retardants
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  Auxins Auxins are producedin the meristem of shoot tips and move down the plant Auxins are effectively used in rooting of difficult to root plants. This has a wide application in vegetative propagation of plants. IBA at 250 ppm and NAA (1- Naphthalene Acetic Acid) were found to increase root development in the propagation of stem cuttings.
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  Some of thesynthetic auxins can be used in removing weeds growing in the farms and agricultural fields. Certain hormones specifically weed out monocots, like grasses and some destroy dicots. for example- 2.2. Dichloro propionic acid removes grasses, while 2, 4 Dichlorophenoxy acetic acid (2, 4-D) & (2, 4, 5 Trichloro phenoxy acetic acid) 2, 4, 5-T) are employed in weeding out the dicots. 2,4-D stimulates excessive uncontrolled growth in broadleaf plants for which it is used as a herbicide
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  Application of NAAreduces flower and fruit drop in Mango. Auxins like Naphthalene acetic acid (NAA) are used in prolonging the dormancy period, thus the storage and shelf life of food in potatoes, corms, bulbs, etc., is prolonged.
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  NAA application bringsuniform flowering and fruit set by inducing ethylene formation in pineapple. NAA application at 10-100 ppm during fruit setting period controls boll shedding in cotton. Auxins and Gibberellins are used in inducing parthenocarpy. Parthenocarpic fruits are seedless, at the same time they are larger and sweetish.
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  These qualities offruits have greater commercial value. Spraying of auxins to fruit plants like orange, lemon apple etc prevents the premature falling of the fruits by formation of abscission layers premature falling cause greater economic loss to cultivators. This can be prevented by the use of auxins.
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  Examples- 1. IAA (IndoleAcetic Acid) 2. IBA (Indole Butyric Acid) 3. NAA (Naphthalene Acetic Acid) 4. 2, 4-D (2, 4 – Dichlorophenxy Acetic Acid) 5. 4-CPA (4-Chloropenoxy Acetic Acid).
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  Gibberellins Gibberellins first isolatedfrom fungal culture. Since then number of gibberellins have been isolated from both the fungus and plants. Gibberellins (GAs) are plant hormones that regulate growth and influence various developmental processes, including stem elongation, germination, dormancy, flowering, sex expression, enzyme induction, and leaf and fruit senescence.
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   GA isused extensively on seedless grape varieties to increase the size and quality of the fruit.  Pre-bloom spray of 20 ppm induces rachis of the fruit cluster to elongate. This creates looser clusters that are less susceptible to disease during the growing season.
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  GA is usedto increase the yield of barley malt and to decrease the time required for this process to occur Application of GA to germinating barley supplements the endogenous content of this hormone and accelerates the production and release of hydrolytic enzymes They can easily degrade the stored carbohydrates.
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  Foliar spray ofGA at 100 ppm during panicle initiation stage enhances the panicle exertion and increases seed weight and yield in hybrid rice GA has also been used to control flower sex expression in cucumbers and squash  GA application tends to promote maleness in these plants
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  GA is alsoapplied to citrus crops, through the actual use depends on the particular crop For example GA3 is sprayed onto oranges and tangerines to delay or prevent or prevent rind-aging, so that fruit can be harvested later without adverse effects on rind quality and appearance For lemons and limes, GA3 synchronizes ripening and enhances fruit size
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  GA is usedextensively to increase the sucrose yield of sugarcane Sugarcane, a normally fast growing C4 member of the Poaceae is sensitive to cooler winter temperatures, which reduce internode elongation and subsequent sucrose yield The adverse effects of cooler temperature can be counteracted by the application of GA3
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   Ethylene ismost widely used plant hormone in agriculture because it regulates so many physiological processes.  Auxins and ACC can trigger the natural biosynthesis of ethylene and in several cases are used in agricultural practice. 1-aminocyclopropane-1-carboxylic acid (ACC)
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  Ethylene A colorless, flammablegas, C2H4 (Ethane gas), having a sweet, unpleasant odor and taste, the first member of the ethylene series, usually obtained from petroleum and natural gas: used as an agent to improve the color of citrus fruits, in the synthesis of polyethylene, ethylene dibromide and ethylene oxide
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  Ethylene is verydifficult to apply in the field as a gas This limitation can be overcome if an ethylene compound is used The most widely used such compound is ethephon or 2- chloro ethyl phosphonic acid (CEPA) (trade name ethrel) Ethrel at 100-250 ppm sprayed at 2-3 leaf stage induce femaleness in cucumber and melons
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  Ethylene can beused for quick ripening of fruits for marketing It helps in degreening of citrus and banana which increases its market acceptability Storage facilities developed to inhibit the ethylene production and promote preservation of fruits have a controlled atmosphere of low O2 concentration and low temperature that inhibits ethylene biosynthesis A relatively concentration of CO2 (3-5%) prevents ethylene action as a ripening promoter
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  Cytokines •The most commonform of naturally occurring cytokinin in plants is zeatin, which was isolated from maize (Zea mays) •Cytokinins have recently been found to play a role in plant pathogenesis. For example, cytokinins have been described to induce resistance against Pseudomonas syringae in Arabidopsis thaliana and Nicotiana tabacum
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  Cytokinins Stimulate celldivision prolong storage life of flowers and vegetables and stimulate bud initiation CK’s is their ability to stimulate chlorophyll synthesis and accelerate chloroplast differentiation in the detached cotyledons in light. CK’s are important in seed germination
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  Cytokines promote hermaphroditeflower e.g Grape Externally applied CK’s are known to exert spectacular effects on the growth and development of plants and excised plant tissue
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  Growth retardants Slow celldivision and cell elongation. Examples i) 2,4 DNC (2,4 Dichlorobenzyl ). ii) CCC (Cycocel) and iii) Alar. Synthetic inhibitors 1. MH- Maleic hydrazide. 2. TIBA- Tri- iodobenzoic acid.
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  Actions Regards stem elongation Preventscell division Accelerate flower initiation Inhibits root development Inhibitors: Supperes the growth of plants
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  Other growth regulators Abscissicacid can be used to obtain uniform harvesting of citrus fruits and cotton balls AMO 1618 (a quaternary ammonium salt) is used in the cultivation of ornamental plants and causes a bushy shape and a study growth of the treated plants Paclobutrazol reduces the problem of biennial bearing in mango
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  Mapiquat chloride, chlormequatchloride (cycocel): used in ornamental plants for shorter internodes and thicker stems (used in poinsettias) It also prevents lodging and increases tillering in cereals Malichydrazide (MH) prevents premature sprouting of onion and potato 2,3,5-T or Triiodo benzoic acid (TIBA): Increases flowering in chrysanthemum
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  Other hormones Florigen thesehormones are synthesized in the older leaves and then transferred to the growing region where it initiates the floral and bud initiation It is mainly responsible for flowering in plants It also called flowering hormones
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  Anthesins its newlydiscovered hormones responsible for flower formation which horticulturists use to induce the early flowering in some plants Morphactins they are synthetic growth regulators which have the various roles and functions as natural growth regulators It has been effective in flowering stimulation, sequence of flowering, position and number of flowers, formation of flowers, inflorescence parthenocarpy, etc
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  Roll of growthhormone in crop production Seed Germination GA significantly accelerates seed germination in many plant species •Pre soaking the seed with GA Such as bhindi and sugar beet increase germination
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  Sex Expression plantgrowth regulators can change the sex of the flowers. Male sterility can be induced in corn by MH (malic hydrozide) It is used in plant breeding for induction of male sterility Application of NAA, IAA and GA at 50 to 100 ppm increases female flowers in pumpkin, cucumber to get more yield
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  oPre Harvest Dropof Fruits flower and fruit drop is a problem in many fruit crops oApplication of NAA 10- 50 ppm in mango, citrus and chilies reduce fruit drop by preventing formation of abscission layer Braking of Dormancy GA, Ethrel, NA are used in breaking dormancy in seeds and buds
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  Physiological process plantgrowth substances have key role in different physiological processes related to growth and development of crops. It is obvious that changes in the level of endogenous hormones due to biotic and abiotic stress alter the crop growth and any sort of manipulation including exogenous application of growth substances would help for yield improvement or at least sustenance of the crop
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  Plant growth hormonesare organic substances produced naturally in the higher plants, controlling growth or other physiological functions at a site remote from its place of production, and active in minute amounts
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  Improved and diseaseresistant crops could easily be made available to farmers if the use of synthetic growth hormones for plantlet regeneration is vigorously pursued. In this technique, hormones like auxins, cytokinines and gibberellins could be made available at reduced cost to users for rapid multiplication of cultivated crops.
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  •Plant hormones havebeen extensively studied for their importance in innate immunity particularly in the dicotyledonous model plant Arabidopsis thaliana (flowering plant ) •Emerging evidence showed that salicylic acid (SA) plays a role in rice basal defense but is differentially required by rice pattern recognition receptor (PRR) and resistance (R) protein- mediated immunity, and its function is likely dependent on the signaling pathway rather than the change of endogenous levels
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  The plant hormonesethylene, jasmonic acid, and salicylic acid (SA) play a central role in the regulation of plant immune responses In addition, other plant hormones, such as auxins, abscisic acid (ABA), cytokinins, gibberellins, and brassinosteroids, that have been thoroughly described to regulate plant development and growth, have recently emerged as key regulators of plant immunity
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  Class Function(s) Practicaluses AuxinsA Shoot elongation Thin tree fruit, increase rooting and flower formation Gibberellins Stimulate cell division and elongation Increase stalk length, increase flower and fruit size Cytokinins Stimulate cell division Prolong storage life of flowers and vegetables and stimulate bud initiation and root growth Plant growth regulator class, associated function(s) and practical uses
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  Ethylene generators Ripening induceuniform ripening in fruit and vegetables Growth inhibitors Stops growth Promote flower production by shortening Internodes Growth retardants Slows growth Retard tobacco sucker Growth
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