2. Salicylic Acid
• Definition
Salicylic acid has been known to be
present in some plant tissues for
quite some time, first discovered
by Baver in 1898 but has only
recently been recognized as a
potential PGS. Salicylic acid is
synthesized from the amino acid
phenylalanine.
Salicylic acid is common throughout
the plant kingdom and is also
found in bacteria. It is an
important regulator of induced
plant resistance to pathogens.
3. Salicylic acid
Background
• active ingredient
in aspirin (acetyl
salicylic acid)
• found in 34 spp.
• Firstly derived
from Salix plant
commonly known
as Willow
6. • SA, synthesized from
transcinnamic acid by way of a
side branch of the
phenylpropanoid pathway, is
involved in thermogenesis in lilies
and pathogen resistance in
tobacco and other species. Until
recently, benzoic acid was thought
to be the immediate precursor of
SA, but increasing evidence is
supporting an alternative, as yet
undefined, route to SA that does
not involve benzoic acid. SA is
metabolized to SA glucoside and
2,5-dihydroxybenzoic acid
glucosyl ester.
Biosynthesis of Salicylic acid
7. Mode of action of Salicylates
• Salicylic acid is calorigenic
substance which produces
heat during fertilization or
reproduction and
temperature rises. This
mechanism is known as CN
resistant respiration e.g.
Sauromatum guttatum.
When temperature
increases, volatile
substances are produced.
This attracts insect
pollinators for pollination.
TAMU
9. Salicylates
• Physiological functions
• 1. Thermogenisis in Arum flowers.
• 2. Plant pathogen resistance-stimulates plant
pathogenesis protein production.
• 3. Reported to enhance longevity of flower (
practice of adding a bit to cut flowers).
• 4. Reported to inhibit ethylene biosynthesis.
• 5. Reported to inhibit seed germination.
• 6. Blocks the wound response.
• 7. Reverses the effects of ABA.
10. Jasmonates
• Jasmonates are represented by
jasmonic acid and its methyl ester.
• They were first isolated from the jasmine
plant in which the methyl ester is an
important product in the perfume industry.
Jasmonic acid is synthesized from linolenic
acid which is an important fatty acid.
12. Biosynthesis of Jasmonate
• It is synthesized from -linolenic
acid, a membrane-derived C18
polyunsaturated fatty acid. The
first specific step in the (–)-JA
biosynthesis pathway, the
conversion of 13(S)-
hydroperoxylinolenic acid to
12,13(S)-epoxylinolenic acid, is
catalyzed by allene oxide
synthase. Wounding a leaf
results in increased AOS activity
and accumulation of (–)-JA. (–
)-JA is metabolized to
hydroxylated products and
amino acid and glycosylated
conjugates.
14. Jasmonates
• Physiological functions
• Inhibition of processes
– seedling longitudinal growth, root length growth,
mycorrhizal fungi growth, tissue culture growth,
embryogenesis, seed germination, pollen germination,
flower bud formation, carotenoid biosynthesis, chlorophyll
formation, rubisco biosynthesis, and photosynthetic
activities
• Promote the processes of
– senescence, abscission, tuber formation, fruit ripening,
pigment formation, tendril coiling, differentiation in plant
tissue culture, adventitious root formation, breaking of seed
dormancy, pollen germination, stomatal closure,
microtubule disruption, chlorophyll degradation,
respiration, ethylene biosynthesis, and protein synthesis
• They play an important role in plant defense by
inducing proteinase synthesis :defence mechanism
against fungi
15. • Definition
– Damage to leaves of several plant species by
herbivores or by other mechanical wounding
induces defense gene activation throughout
the plants within hours. An 18-amino acid
polypeptide, called systemin, has been
isolated from tomato leaves by this process.
Systemin
16. • Systemin is produced at the site of
wounding, then is loaded into the phloem,
transported with similar rates as sucrose
from source to sink
• Systemin is cleaved from a larger protein,
called prosystemin, by a protease.
• the regulation of this protease is unknown,
but expression of prosystemin is higher
after wounding
Systemin
17. • Model for the activation of defense genes in
tomato in response to wounding and insect
attack. After wounding, systemin is released
from its precursor prosystemin by proteolytic
processing. Systemin subsequently binds a
membrane-bound receptor to initiate an
intracellular signaling cascade, including the
activities of a MAP kinase, a phospholipase,
a calcium dependent protein kinase, an
extracellular alkalinization, and the release
of linlenic acid from membranes. Linolenic
acid is converted to jasmonic acid, a
messenger for early defense gene
activation. Catalytic activity of
polygalaturonase, an early gene, leads to
generation of hydrogen peroxide acting as a
second messenger for late gene activation.
R, receptor; MAPK, MAP kinase; Ca2+PK;
calcium dependent protein kinase; PLA2,
phospholipase A2; LA, linolenic acid; JA,
jasmonic acid; pm, plasma membrane.
Mode of action of Systemin
18. Systemin
• Physiological functions
• It is a powerful inducer of over 15 defensive genes when supplied to the
tomato plants at levels of fmol/plant.
• Translocation
– Systemin is readily transported from wound sites and is considered to
be the primary systemic signal. The polypeptide is processed from a
200-amino acid precursor called prosystemin, analogous to polypeptide
hormones in animals. However, the plant prohormone does not possess
typical dibasic cleavage sites, nor does it contain a signal sequence or
any typical membrane-spanning regions. The signal transduction
pathway that mediates systemin signaling involves linolenic acid release
from membranes and subsequent conversion to jasmonic acid, a potent
activator of defense gene transcription. The pathway exhibits analogies
to arachidonic acid/prostaglandin signaling in animals that leads to
inflammatory and acute phase responses.
19. alpha, beta and gamma
tocopherols (Vitamin E)
• Tocopherols are lipophilic antioxidants
synthesized exclusively by photosynthetic
organisms and collectively constitute vitamin E,
an essential nutrient for both humans and
animals.
• alpha (E1), beta (E2) and gamma(E3) tocopherol
• sources: plant oils (corn, peanut, wheat germ),
green leafy vegetables, meat, eggs
• value resides in the antioxidant properties of
vitamin E (may prevent the formation of
peroxides)
20. III. Vitamin E
A. Forms
1. Alpha-Tocopherol
2. Tocopherols
3. Tocotrienols
4. Each has different potencies
B. Functions
1. Antioxidant (fat-soluble)
a. Protects against oxidation and free
radicals
21. Tocopherols
• Vitamin E refers to a family of eight molecules having a
chromanol ring (chroman ring with an alcoholic hydroxyl
group) and a 12-carbon aliphatic side chain containing
two methyl groups in the middle and two more methyl
groups at the end. For the four tocopherols the side
chain is saturated, whereas for the four tocotrienols the
side chain contains three double-bonds, all of which
adjoin a methyl group. The four tocopherols and the four
tocotrienols have an alpha, beta, gamma and delta form
-- named on the basis of the number and position of the
methyl groups on the chromanol ring. The alpha form
has three methyl groups, the beta & gamma forms have
two methyl groups and the delta for has only one methyl
group.
25. Biosynthesis of Tocopherol
• Tocopherol biosynthetic
pathway. This figure represents
the enzymatic reactions and
intermediates that are involved
in tocopherol synthesis. 1,
HPPD. 2, Homogentisate phytyl
transferase (HPT). 3, 2-Methyl-
6-phytyl-1,4-benzoquinone
(MPBQ) methyltransferase. 4,
TC. 5, -Tocopherol
methyltransferase ( -TMT).
HPP, p-
Hydroxyphenylpyruvate; HGA,
homogentisic acid; SAM, S-
adenosyl L-Met
26. Mode of action of alpha Tocopherol
biological activity of Vitamin E which attracts the
most interest is the prevention of lipid
peroxidation. Alpha-tocopherol is the most
active tocopherol against peroxyl
radicals (LOO.) and delta-tocopherol is the least
active (alpha>beta=gamma>delta). The anti-
oxidant activity of Vitamin E is based on the
ease with which the hydrogen on the hydroxyl
group of the chroman ring can be donated to
neutralize a free radical (creating a more stabile
tocopheroxyl radical). As with phospholipids, the
polar chroman ring tends to stay near the edges
of the membrane, whereas the hydrophobic
core will be buried deep into the membrane.
When a phospholipid tail becomes peroxidized
by a free radical, the tail becomes more polar
and migrates to the surfaces where it can meet
the tocopherol chroman ring to be neutralized,
while forming a tocopheroxyl radical. The
tocopheroxyl radical can be reduced (restored)
to tocopherol directly by Ubiquinol or Vitamin C -
- and then by glutathione or lipoic acid (via
Vitamin C), which are in turn reduced by NADH
or NADPH.
27. Tocopherol
• Physiological functions
• Among the best characterized functions of tocopherols in cells is
their ability to scavenge and quench reactive oxygen species and
lipid-soluble byproducts of oxidative stress. In addition to being
lipophilic, tocopherols are capable of donating a single electron to
form the resonance-stabilized tocopheroxyl radical. Tocopherols are
unique in this regard to other phenolic antioxidants, such as
hydroxyquinones, which must donate two electrons to attain a stable
structure. Tocopherols can also donate two electrons, which results
in opening of the chromanol ring to form the corresponding
tocoquinone derivative. These combined molecular characteristics
allow tocopherols to protect polyunsaturated fatty acids from lipid
peroxidation by scavenging lipid peroxyl radicals that propagate lipid
peroxidation chain reactions in membranes.Though direct evidence
is lacking, tocopherols are thought to play similar roles in protecting
the polyunsaturated fatty acid-rich plastid membrane from lipid
peroxidation
28. Fusicoccin
• In the simplest case, germinating spores or hyphae
penetrate the plant tissues through wounds of the
epidermatic tissue, wounds of the cuticle or open
stomata. Some specialists like Fusicoccum amygdali that
belongs like most of the following examples to the Fungi
imperfecti secrete a terpenoid (fusicoccin) that increases
the influx of potassium into the cells of the stomata and
induces thereby a permanent opening of the stomata.
The consequent high loss of water causes finally the
perishing of the plant. Fusicoccin is therefore also known
as a wilting toxin.
• Fusicoccin was first identified as a
phytotoxin in the 1960s
30. • Model for the mechanism of fusicoccin
activation of H+-ATPases. (A) A pair of
plasma membrane H+-ATPases
associate to form an active dimer. The
activity of the pump is limited by the
autoinhibitory effect of the C terminus
of each monomer. (B) Dimers of 14-3-
3 proteins form a transient complex
with the C terminus of the H+-ATPase
and possibly another protein. When
the autoinhibitory C terminus is bound
to the 14-3-3 protein, the activity of the
H+-ATPase increases, but the effect is
transient because of the instability of
the complex. (C) The binding of
fusicoccin to the complex stabilizes the
complex, locking the H+-ATPase into
an active state.
Mode of action of Fusicoccin
31. • Physiological function
• FC causes membrane hyperpolarization and proton extrusion in nearly all
plant tissues. Treatment of coleoptiles and stem sections with FC leads to a
transient growth response, a result that provides support for the acid growth
hypothesis for auxin-induced growth. But whereas auxin-induced proton
extrusion has a lag time of about 10 minutes and is inhibited by
cycloheximide, FC-induced proton extrusion begins after only 1 to 2
minutes, and the response is insensitive to cycloheximide. Moreover, FC-
treated cells can acidify down to a much lower extracellular pH than auxin-
treated cells can (pH 3 versus pH 4).
• Because of these effects, FC has sometimes been referred to as a "super
auxin." However, FC acts by a mechanism entirely different from that of
auxin. For example, FC does not stimulate the expression of any of the
auxin-induced genes, nor can it mimic the effects of IAA on other
developmental processes, such as cell division. Thus the effects of FC on
plants are much more limited than those of IAA
FUSICOCIN
Fusicoccin
32. Triacontanol
• Triacontanol (TRIA) is a saturated long-chain
alcohol that is known to have a growth
promoting activity when exogenously supplied to
a number of plants
• Triacontanol (TRIA) is a 30-carbon, straight
chain primary alcohol, and a natural constituent
of wax in the cuticle of plants. TRIA, in
nanomolar quantities,
• common sources include alfalfa cotton, apples,
and sunflower seeds
•
33. • Physiological functions
• increased dry weight, CO2-fixation, reducing sugars,
soluble proteins, free amino acids, chlorophyll content
and yield in many crop plants
• Addition of TRIA was reported to stimulate that
elongation of hypocotyl segments of soybean also
stimulate the elongation of shoots in B.
• napus.
• This fatty acid is found in many plants. It increases
growth rates and yields up to 25%, and increases the
protein content, even in darkness, when most plants are
dormant. It seems to enhance the growth of plants
without increasing their consumption of nitrogen.
Triacontanol
34. Turgorins
• Nyctinastic movement has been believed
to be controlled by Schildknecht’s
turgorins which induce
• leaf-closing movement of the plants [4].
Schildknecht said that all leaf-movements
are controlled by
• turgorin, a new class of phytohormone
which regulates the turgor of the plants.
