Plant Growth Hormones : Plant Growth Hormones Nazir Ahmad 10-NUAS-203
National University of Agricultural Sciences Plant Growth Hormones : Plant Growth Hormones Hormone (from the Greek word hormaein, meaning "set in motion")
Man made - Plant growth regulator ( PGR)
PGR is defined as an organic compound, either natural or synthetic, that modifies or controls one or more specific physiological processes within a plant. Transport : Transport Are produced in one part of a plant and then transported to other parts, where they initiate a response.
They are stored in regions where stimulus are and then released for transport through either phloem or mesophyll when the appropriate stimulus occurs. Classes : Classes Major classes of plant growth regulators (hormones) are:
Abscisic acid Auxins : Auxins Auxins : Auxins Frits Went (1926) determined auxin enhanced cell elongation.
Auxins derive their name from the Greek word auxano -- "I grow/increase".
Synthetic Auxins as weed killers Auxins : Auxins Growth promoting chemicals
Promote cell division and cell elongation
Primary plant auxin is indole acetic acid (IAA).
IBA, NAA, 2-4D (2,4-dichlorophenoxyacetic acid)
Useful in phototropism, geotropism, apical dominance, and root formation
Apical dominance- terminal buds prevent the development of lateral buds on plant stem Auxins Functions : Auxins Functions Apical dominance.
terminal buds prevent
the development of
lateral buds on plant stem.
What happened if we remove
Pinching Pinching : Pinching Pinching = removing the terminal bud
Pinching - stops flow of Auxins down the stem and allows side shoots to develop
Produces bushy, well-branched crops Auxins Functions : Auxins Functions Root initiation and
Used on cuttings
to help stimulate
root growth Phototropism : Phototropism Phototropism- plant growth toward a light source Gravitropism (geotropism) – plant response to gravity. Geotropism- plant growth in response to gravitational forces : Gravitropism (geotropism) – plant response to gravity. Geotropism- plant growth in response to gravitational forces Auxins – move to lowest side and cause stem tissue to elongate downward. Gibberellin : Gibberellin Growth promoting chemicals Gibberellins (GAs) are a group
of diterpenoid acids Gibberellins : Gibberellins Gibberellins are named after the fungus Gibberella
fujikuroi which causes rice plants to grow abnormally tall. In 1930's, Ewiti Kurosawa and colleagues were studying plants suffering from "foolish seedling" disease in rice.
Also known as Gibberellic acid or GA
Second important growth Hormone. More than 60 types of Gibberellins are known
Are produced in the shoot apex primarily in the leaf
primordial (leaf bud) and root system
GA translocates easily in the plant (able to move freely) in both directions – because produced in not only shoot apex but also in the root structure. Gibberellins : Gibberellins Stimulate stem growth
through cell elongation
and cell division
Involved in overcoming
dormancy in seeds and buds. Internodes Elongation : Internodes Elongation Gibberellins cause internodes to stretch in relation to light intensity.
High light intensity = no stretch
Low light intensity = long internodes. Leaves are raised to capture light Gibberellins : Gibberellins Used commercially in:
of flowers Increasing fruit size of seedless grapes : Increasing fruit size of seedless grapes Grapes are treated with GA to
increase size. Cytokinins : Cytokinins Cytokinins : Cytokinins Adenine or adenine-like compounds induce cell division in plant tissue culture. Miller, Skoog and their coworkers isolated the growth factor responsible for cellular division from a DNA preparation calling it kinetin which belongs to a class of compounds called Cytokinins. (1950) Cytokinins : Cytokinins Promotes cell division
Found in all tissues with considerable cell division.
Roots supply cytokinins upward to the shoots.
Interact with auxins to influence differentiation of tissues (may be used to stimulate bud formation).
As roots begin to grow actively in the spring, they produce large amounts of cytokinins that are transported to the shoot, where they cause the dormant buds to become active and expand. Cytokinins vs. Auxins : Cytokinins vs. Auxins In stems – Auxins inhibit lateral shoots, Cytokinins promote lateral shoots
In roots – Auxins promote root branching, Cytokinins inhibit root branching
Work together to control cell differentiation and cell division. Ethylene C2H2 : Ethylene C2H2 In the 1800s, it was recognized that street lights that burned gas, could cause neighboring plants to develop short, thick stems and cause the leaves to fall off. In 1901, Dimitry Neljubow identified that a byproduct of gas combustion was ethylene gas and that this gas could affect plant growth.
R. Gane showed that this same gas was naturally produced by plants and that it caused faster ripening of many fruits.
Synthesis of ethylene is inhibited by carbon dioxide and requires oxygen. Ethylene : Ethylene Gaseous hormone
Produced in the actively growing meristems of the plant, in senescing ripening or ageing fruits, in senescing (ageing or dying) flowers, in germinating seeds and in certain plant tissues as a response to bending, wounding.
Ethylene as a gas, diffuses readily throughout the plant. Ethylene : Ethylene May promote leaf senescing and abscission (leaf fall).
Increases female flowers in cucumbers (economically - will increase fruit production).
Degreening of oranges, lemons and grapefruit – ethylene gas breaks down chlorophyll and lets colors show through. Abscisic Acid (ABA) : Abscisic Acid (ABA) In 1940s, scientists started searching for hormones that would inhibit growth and development, what Hemberg called dormins.
In the early 1960s, Philip Wareing confirmed that application of a dormin to a bud would induce dormancy.
F.T. Addicott discovered that this substance stimulated abscission of cotton fruit. he named this substance abscisin.
Abscisin is made from carotenoids. Abscisic Acid : Abscisic Acid Widespread in plant body – moves readily through plant.
ABA appears to be synthesized (made) by the leaves.
Interacts with other hormones in the plant, counteracting the growth – promoting the effects of Auxins & gibberellins. Abscisic Acid : Abscisic Acid Involved with leaf and fruit abscission (fall), onset of dormancy in seeds and onset of dormancy (rest period) in perennial flowers and shrubs
also plays important role in controlling stomatal opening and closing PGR and Cancer : PGR and Cancer Plant stress hormones activate cellular responses, including cell death, to diverse stress situations in plants. Researchers have found that some plant stress hormones share the ability to adversely affect human cancer cells . For example, sodium salicylate has been found to suppress proliferation of lymphoblastic leukemia, prostate, breast, and melanoma human cancer cells.
Jasmonic acid, a plant stress hormone that belongs to the jasmonate family, induced death in lymphoblastic leukemia cells.
Methyl jasmonate has been found to induce cell death in a number of cancer cell lines. :