The pathway of ABA synthesis beginning with zeaxanthin. The steps in isoprenoid and carotenoid synthesis before zeaxanthin are reviewed elsewhere (Cunningham and Gantt, 1998; Rohmer, 1999; Hirschberg, 2001; Rodrı́guez-Concepción and Boronat, 2002). VDE, Violaxanthin de-epoxidase.
Plant hormone biosysnthesis and function amjad
Dr. S.S. Gill
3. Where produced or found in plants?
4. Biosynthesis of plant hormones
• Plant Hormones (Phytohormones)-
Plant hormones are signal molecules produced
within the plant , which is transmits its effects
from one part of the plant to another.
• Hormones- A compound produced in one
area of an organism and has an affect on
an another area.
• The word hormone is derived from Greek,
meaning set in motion.
Where produced or found in plants?
1. Auxin- Embryo of seed, meristem of apical bud, young leaves.
2. Gibberellins- Meristem of apical bud and roots, young leaves, embryo.
3. Cytokinins- Synthesized in roots and transported to other organ.
4. Abscisic acid- Leaves, stems, roots, green fruit.
5. Ethylene- Tissue of ripening fruit, nodes of stems, ageing of leaves and
AUXINS (Indole 3- acetic acid)
• Growth or movement of a organism toward or
away from a source of light.
Darwin's study of phototropism.
Boysen-Jensen showed a chemical messenger
was being transported to the rest of the plant.
Went discoverd the
signal that was
transported from the
tip to the rest of the
plant and named the
Paal discovered that the chemical signal
induced cell growth.
1. Auxins Biosynthesis
• Two major pathway of auxins biosynthesis:-
1. Try- dependent pathway
IPA pathway (Indole 3- pyruvic acid)
TAM pathway (Tryptamine)
IAN pathway (Indole 3- acetonitrile)
IAM pathway (Indole 3- acetamide)
2. Try- independent pathway
• In trp- independent IAA biosynthesis, indole 3- glycerol
phosphate or indole is the likely precursors.
• Cell elongation:- By increasing cell wall
extensibility In stems and coleoptiles.
• Cell differentiation:- Xylem and Phloem are
regulated by auxin concentration.
• Regulates development of fruits:- Auxin produces
in the endosperm and embryo of developinng
• Function in phototropism.
• Apical dominance.
• Root growth.
1. Gibberellins were discovered by Eiichi Kurosawa in japan
during worked on fungal disease(“Bakanae” or “Foolish
Seedling” ) on rice.
2. This disease caused by “Gibberella fujikuroi” .
3. It was first isolated in 1935 byTeijiro Yabuta and Sumuki, from
fungal strains (Gibberella fujikuroi) provided by
Kurosawa. Yabuta named the isolate as gibberellin.
1. gibberellins are synthesized via the terpenoid
2. Based on isoprene units:
3. Biosynthesis occur in 3 part of plant-
Plastid, E.R., Cytosol
• Stem elongation:-
• Flowering and sex determination
• Promotes seed and bud germination
• Stimulates shoot elongation and leaf growth
• Affect root growth and differentiation
• Fruit set
• Cytokinins are adinine derivatives .
• Carlos Miller (1955) – first cytokinin isolated
from herring sperm, named kinetin.
• Carlos Miller and Letham (1961) – first
naturally occurring cytokinin found in plants,
later called zeatin.
• ABA plays the role of strees hormone.
• Identified by Fredrick T. Addicott during studying
on abscission of cotton fruits.
• The discovery of ABA based on two different
physiological function:- 1960
• 1. “abscisin “ cousing abscision of fruits
• 2. “dormin” including the dormancy of bud
• In 1965 abscisin and dormin are same substance
and then term arise name abscisic acid.
The pathway of ABA synthesis beginning with zeaxanthin.
ETHYLENE (gaseous hormone)
– Tree defoliation- coal gas streetlamps
– Ethylene - active component of coal gas
– Herbert Henry Cousins - discharge of ethylene in store
– R. Gane - natural product of plant metabolism
– Ethylene is the simplest known olefin (its
molecular weight is 28), and it is lighter than air
under physiological conditions
– It is flammable and readily undergoes oxidation.
– Ethylene can be oxidized to ethylene oxide:
– and ethylene oxide can be hydrolyzed to ethylene
– In most plant tissues, ethylene can be completely
oxidized to CO2
Ethylene Ethylene oxide Oxalic acid
• Promotes the ripening of some fruits:- the enzymatic
breakdown of the cell wall; starch hydrolysis; sugar
accumulation; organic acids and phenolic compounds
(tannins) disappear; chlorophyll loss and anthocyanins
and carotenoids accumulation; aroma and flavor
components produced; drying for some fruits.
• Leaf epinasty:-
The downward bending of a leaf or other plant part
• Fruit ripening
• maintains the hooks of dark-growing seedling