Plant Growth Regulators : Plant Growth Regulators Mr. Mangesh D.Wandhare
M.Pharm (Pharmacognosy & Phytochemistry)
Assistant Professor, Channabaweshwar Pharmacy College ( Degree) Latur ( M.S.) Slide 2: The growth & development of plants is regulated by a number of
chemical substances which together exert a complex interaction to
meet the needs of the plant. These chemical substances regulates plant growth ( either stimulates or inhibits growth ) & as such commonly referred to as “Plant Growth Regulators”
These may be Endogenous or Exogenous substances.
Five groups of Plant hormones are well established
Abscisic acid & its derivatives Slide 3: Characteristics of Plant Growth Hormones
Specific in their action
Active in very low concentrations
Regulation of cell enlargement, cell division, cell differentiation,
organogenesis, senescence & cell dormancy.
Role of Plant Growth Hormones
In Cell & Tissue cultures
Production of secondary metabolites ( better yield ) These substances occur in all higher plants. Slide 5: Auxins
Studied in 1931 by Dutch workers by isolating two growth regulating acids ( auxin – a & auxin – b) obtained from human urine & cereals respectively
These had similar properties to indole – 3 - acetic acid ( IAA)
Indole – 3 - acetic acid ( IAA) found to be major auxin of plants, found particularly in actively growing tissues
Precursors like indoleacetaldehyde, indoleacetonitrile & indolepyurvic acid
These all are derived from Tryptophan. Slide 7: Effects of Auxins
Cell elongation i.e. stem length
Inhibition of root growth
Adventitious root production
Fruit - setting in the absence of pollination
In Tissue culture technique auxins plays vital role since
auxins is responsible for growth as well as secondary
metabolite production in excised plants. Slide 8: Mechanism of action
Oxidative degradation of IAA to give number of products is controlled by IAA Oxidase enzyme
Ortho - diphenols inhibit the action of enzyme hence
stimulation of growth by themselves
Monophenols promote the action of the enzyme & thus
inhibit growth. Slide 14: Presence of IAA in Plants
IAA present in conjugation with aspartic acid, glutamic acid, glycine, sugars &
cyclitols serving inactive storage forms of hormone for plant detoxification
Naphthalene -1-acetic acid ( NAA), 2,4 – dichlorophenoxyacetic acid ( 2,4 –D),
IBA & NAA in combination are used in rooting of cuttings
2,4 –D & 2,4,5 –T are used both as plant growth regulators & in higher
concentrations as selective weed killers especially for dicot plants
The addition of IAA, NAA, 2,4 - D in tissue cultures of ergot has led to increase
yield of indole alkaloids.
IAA & derivatives of IAA are found to be most important Plant growth
hormones in excised parts of plant. Slide 15: Gibberellins
These are endogenous plant growth regulators
About 40 gibberellins occur in plants while others are present in some fungi
Kurosawa, a japanese physiologist is credited for initiating the discovery of
gibberellin from fungus Gibberella fujikuroi grown on rice in 1926
According to Paleg , gibberellins are compounds having gibbane skeleton &
biological activity in stimulating cell division or cell elongation or both
Yabuta & Hayashi isolated a crystalline sample of of the active material which
they were called “ Gibberellins” Slide 16: Chemistry of Gibberellins Gibberellins are tetracyclic diterpene acids Slide 19: Functions of Gibberellins
Breaking of seed dormancy
Increasing Fruit Size
Flowering and sex expression
Fruit growth and parthenocarpy
Malting Slide 20: Mechanism of action
Acts by inducing activity of gluconeogenic enzymes during early
stages of seed germination
Gibberellins also induces the synthesis of α – amylase & other
hydrolytic enzymes during germination of monocot seeds
Gibberellins also mobilizes seed storage reserves during
germination & seedling emergence. Slide 21: Effect of Gibberellins on Secondary Metabolite Production
Kaul & Kapoor reported 33 % increase in Chenopodium ambrosioides while
50 % increase in Anethum spp. & 30 % increase in A.sowa
At lower doses of GA treatment there was no significant changes in the
carvone content of the oil, but at higher concentration there appeared to be a
slight increase over the official limit ( 53%, B.P.1958)
Reduction in alkaloid content has been noted in Vinca, Datura, Hyoscyamus,
No any change in Fixed oil content observed after treatment of Gibberellins. Slide 22: Cytokinins
Cytokinins (CK) are a class of Plant growth substances that promote cell division or cytokinesis , in plant roots & shoots
They are involved primarily in cell growth and differentiation but also affect apical dominance , axillary bud growth & leaf senescence Chemistry of Cytokinins Slide 23: The naturally occurring cytokinins are zeatin, N6 dimethyl aminopurine & N6 – Δ 2 - isopentenyl aminopurine The synthetic cytokinins are Kinetin , adenine, 6 – benzyl adenine , benzimidazole & N, N’ - diphenyl urea Slide 24: History In 1913, Gottlieb Haberlandt discovered that a compound found in phloem had
the ability to stimulate cell division (Haberlandt, 1913).
In 1941, Johannes van Overbeek discovered that the milky endosperm from
coconut also had this ability. He also showed that various other plant species
had compounds which stimulated cell division (van Overbeek, 1941).
In 1954, Jablonski and Skoog reported that vascular tissues contained
compounds which promote cell division (Jablonski and Skoog, 1954).
The first cytokinin was isolated from herring sperm in 1955 by Miller and his
associates (Miller et al., 1955). This compound was named kinetin because of
its ability to promote cytokinesis.
Hall and deRopp reported that kinetin could be formed from DNA degradation
products in 1955 (Hall and deRopp, 1955).
In 1961 Miller isolated natural cytokinin from corn ( Zeatin ) Slide 25: Biosynthesis & Metabolism of Cytokinins A product of the mevalonate pathway called isopentenyl pyrophosphate is isomerized.
This isomer can then react with adenosine monophosphate with the aid of an enzyme called isopentenyl AMP synthase resulting to isopentenyl adenosine-5'-phosphate (isopentenyl AMP). This product can then be converted to isopentenyl adenosine by removal of the phosphate by a phosphatase and further converted to isopentenyl adenine by removal of the ribose group. Isopentenyl adenine can be converted to the three major forms of naturally
occurring cytokinins. Other pathways or slight alterations of this one probably
lead to the other forms. Degradation of cytokinins occurs largely due to the enzyme cytokinin oxidase. Slide 26: Mechanism of Action
Kinetin are reported to play the role in nucleic acid metabolism & protein
In plant metabolism ,it is proposed that some t – RNA contain cytokinin like
They have an action on some enzymes responsible for formation of certain
Cytokinins are reported to increase markedly Sennoside content in Tinnevelly Senna leaves
In opium , reduce alkaloid content.
In Duboisia hybrids, the cytokinin activity present in extract of a seaweed , shows marked increase in hyoscine content. Effects on production of secondary metabolites Slide 27: Cytokinins act in concert with auxin, another plant
hormone stimulating Cell expansion Slide 28: Ethylene Ethylene serves as a hormone in plants.
It acts at trace levels throughout the life of the plant by stimulating
or regulating the ripening of fruit, the opening of flowers, and
the abscission (or shedding) of leaves.
Commercial ripening rooms use "catalytic generators" to make
ethylene gas from a liquid supply of ethanol. Typically, a gassing
level of 500 to 2,000 ppm is used, for 24 to 48 hours.
Care must be taken to control carbon dioxide levels in ripening
rooms when gassing, as high temperature ripening (68F) has been
seen to produce CO2 levels of 10% in 24 hours. Slide 29: History of ethylene in plant biology Ethylene has been used since the ancient Egyptians, who would gash figs in order to stimulate ripening (wounding stimulates ethylene production by plant tissues).
In 1864, it was discovered that gas leaks from street lights led to stunting of growth, twisting of plants, and abnormal thickening of stems.
In 1901, a Russian scientist named Dimitry Neljubow showed that the active component was ethylene. Doubt discovered that ethylene stimulated abscission in 1917.
In 1934 Gane reported that plants synthesize ethylene.
In 1935, Crocker proposed that ethylene was the plant hormone responsible for
fruit ripening as well as senescence of vegetative tissues. Slide 30: Ethylene biosynthesis in plants The enzymatic oxidation of ACC produces ethylene in plants. Ethylene is biosynthesized from the amino acid methionine to S-Adenosyl – L -
methionine (SAM) by the enzyme Met Adenosyl transferase.
SAM is then converted to 1- aminocyclopropane-1-carboxylic-acid (ACC) by the
enzyme ACC Synthase (ACS) The final step requires Oxygen and involves the action of the enzyme ACC
Oxidase (ACO) Slide 31: Growth responses due to Ethylene effect
Flower petal discoloration
Inhibition of stem & root growth Slide 32: Commercial Uses
For promotion of Flowering & fruit ripening.
Induction of fruit abscission, breaking dormancy &
stimulation of latex flow in rubber trees. Slide 33: Abscissic acid ( ABA)
It is a Plant Growth Inhibitor
A diffusible abscission accelerating substance was found by Osborne (1955) in senescent leaves
Carns et al. isolated several abscission accelerating substances from cotton plants & named them as abscission I & abscission II Slide 34: Biosynthesis
Abscisic acid (ABA) is an isoprenoid plant hormone, which is
synthesized in the MEP Pathway
The C15 backbone of ABA is formed after cleavage of
C40 carotenoids MEP.
Zeaxanthin is the first committed ABA precursor; a series of enzyme catalyzed epoxidations and isomerizations via vialoxanthin
Final cleavage of the C40 Carotenoid by a dioxygenation reaction yields the proximal ABA precursor, xanthoxin, which is then further oxidized to ABA.
Abamine has been designed, synthesized, developed and then patented as the first specific ABA biosynthesis inhibitor, which makes it possible to regulate endogenous level of ABA. Slide 35: Location and timing of ABA biosynthesis
Released during desiccation of the vegetative tissues and when roots encounter soil compaction
Synthesized in green fruits at the beginning of the winter period
Synthesized in maturing seeds, establishing dormancy
Mobile within the leaf and can be rapidly translocated from the roots to the leaves by the transpiration stream in the xylem
Produced in response to environmental stress , such as heat stress, water stress, salt stress
Synthesized in all plant parts, e.g., roots, flowers, leaves and stems. Slide 36: Mechanism of Action
It inhibit the GA induced synthesis of α – amylase & other hydrolytic enzymes
During maturation , ABA accumulates in many seeds & helps in seed dormancy
ABA concentrations are found to be enhanced in stress conditions like , mineral deficiency , injury , draught & flooding
ABA serves as an potential antitranspirant by closing the stomata, when applied to leaves Slide 37: Effects
Antitranspirant - Induces stomatal closure, transpiration
to prevent water loss.
Inhibits Fruit ripening
Responsible for seed dormancy by inhibiting cell growth – inhibits
Inhibits the synthesis of Kinetin nucleotide
Down regulates enzymes needed for Photosynthesis Slide 38: Other Plant Growth Retardants
There commercial uses are yet to be reported
Morphactins : Group of Synthetic substances which are potent
inhibitor of auxin transport causing tropic responses ,
reduction of apical dominance & promoting lateral growth.
e.g. Chloroflurecol methyl , Flurecol butyl & TIBA ( 2,3,5 – triiodobenzoic acid Slide 39: References
Textbook of Pharmacognosy by Trease & Evans
Textbook of Pharmacognosy by C. K .Kokate & S. B.
Gokhale , Fourty Fourth edition
Wikipedia Slide 40: Thank You