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Plant Hormone

The Charles Darwin was the first scientist to dabble in Plant Hormone Research.
Darwin in his book "The Power of Movement in Plants" presented in 1880 first describes the effects of light on movement of canary grass (Phalaris canariensis) coleoptiles. Following 5 types of hormones are found in plants-


Auxins were the first plant hormones discovered. Charles Darwin was among the first scientists to dabble in plant hormone research. In his book "The Power of Movement in Plants" presented in 1880, he first describes the effects of light on movement of canary grass (Phalaris canariensis) coleoptiles.

Auxins- These were discovered by Charles Darwin in 1880. Following given properties and functions of Auxins-
•    Stimulates cell elongation
•    Stimulates cell division in the cambium and, in combination with cytokinins in tissue culture
•    Stimulates differentiation of phloem and xylem
•    Stimulates root initiation on stem cuttings and lateral root development in tissue culture
•    Mediates the tropistic response of bending in response to gravity and light
•    The auxin supply from the apical bud suppresses growth of lateral buds
•    Delays leaf senescence
•    Can inhibit or promote (via ethylene stimulation) leaf and fruit abscission
•    Can induce fruit setting and growth in some plants
•    Involved in assimilate movement toward auxin possibly by an effect on phloem transport
•    Delays fruit ripening
•    Promotes flowering in Bromeliads
•    Stimulates growth of flower parts
•    Promotes (via ethylene production) femaleness in dioecious flowers
•    Stimulates the production of ethylene at high concentrations


Gibberllins- This plant hormone was discovered by Japanese scientist Kurosava in 1926. Following given properties and functions of Gibberllins-

•    Stimulate stem elongation by stimulating cell division and elongation.
•    Stimulates bolting/flowering in response to long days.
•    Breaks seed dormancy in some plants which require stratification or light to induce germination.
•    Stimulates enzyme production (a-amylase) in germinating cereal grains for mobilization of seed reserves.
•    Induces maleness in dioecious flowers (sex expression).
•    Can cause parthenocarpic (seedless) fruit development.
•    Can delay senescence in leaves and citrus fruits.

Cytokinins- The first cytokinin was isolated from herring sperm in 1955 by Miller and his associates. Following given properties and functions of Cytokinins-

•    Stimulates cell division.
•    Stimulates morphogenesis (shoot initiation/bud formation) in tissue culture.
•    Stimulates the growth of lateral buds-release of apical dominance.
•    Stimulates leaf expansion resulting from cell enlargement.
•    May enhance stomatal opening in some species.
•    Promotes the conversion of etioplasts into chloroplasts via stimulation of chlorophyll synthesis.

Abscisic Acid or ABA- The Abscisic Acid or ABA was first discovered by by Frederick Addicott and his associates in 1963. Following given properties and functions of  Abscisic Acid or ABA.

•    Stimulates the closure of stomata (water stress brings about an increase in ABA synthesis).
•    Inhibits shoot growth but will not have as much affect on roots or may even promote growth of roots.
•    Induces seeds to synthesize storage proteins.
•    Inhibits the affect of gibberellins on stimulating de novo synthesis of a-amylase.
•    Has some effect on induction and maintanance of dormancy.
•    Induces gene transcription especially for proteinase inhibitors in response to wounding which may explain an apparent role in pathogen defense.


Ethylene- In 1934 Gane reported through his research that plants synthesize ethylene. In 1935, Crocker proposed that ethylene was the plant hormone responsible for fruit ripening as well as inhibition of vegetative tissues. This is only hormone present in gaseous form. Following give properties and functions of ethylene.
•    Stimulates the release of dormancy.
•    Stimulates shoot and root growth and differentiation (triple response)
•    May have a role in adventitious root formation.
•    Stimulates leaf and fruit abscission.
•    Stimulates Bromiliad flower induction.
•    Induction of femaleness in dioecious flowers.
•    Stimulates flower opening.
•    Stimulates flower and leaf senescence.
•    Stimulates fruit ripening.

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