Biosynthesis of gibberellins.pptx

BIOSYNTHESIS, TRANSLOCATION,
PHYSIOLOGICAL ROLE AND
MECHANISM OF GIBBERELLINS
BY
B. PAVAN KUMAR NAIK
1st YEAR Ph.D
DEPARTMENT OF HORTICULTURE
FACULTY OF AGRICULTURE
ANNAMALAI UNIVERSITY

1 INTRODUCTION OF GIBBERELLINS
2 BIOSYNTHESIS AND METABOLISM OF GIBBERELLIN
3 ENDOGENOUS GA1 LEVELS ARE CORRELATED WITH TALLNESS
4 GIBBERELLINS TRANSPORT IN PLANTS
5 ENVIRONMENTAL CONDITIONS CAN ALTER THE TRANSCRIPTION OF
GIBBERELLIN BIOSYNTHESIS GENES
6 MECHANISM OF GIBBERELLINS
7 PHYSIOLOGICAL ROLE
CONTENTS

 The discovery of gibberellins is quite fascinating and dates back to about the same period when
auxins were discovered, but it was only after 1950s they came into prominence.
 A young Japanese scientist Kurosawa - rice seedlings - fungus Gibberella fujikuroi.
 Cause – Excess shoot elongation, yellowish green leaves taller plants – poorly developed
grains.
 These are the symptoms of ‘Backanae disease’ (meaning foolish) which is known to Japanese for
over a century.
 In 1926 - filtered extract of this fungus - Backanae disease in healthy rice seedlings.
 In 1935, Yabuta isolated the active substance which was quite heat stable and gave it the name
gibberellin.
INTRODUCTION OF GA

In the 1930s Japanese scientists
succeeded in obtaining impure
crystals of two fungal growth-
active compounds, which they
termed gibberellin A and B.
Conti…

Structure of Gibberellic acid
Tokyo University isolated 3 gibberellins- gibberellin A
1. gibberellin A1,
2. gibberellin A2, and
3. gibberellin A3
 Gibberellin A3 and gibberellic acid proved to be identical.

The structural feature that all
gibberellins have in
common, and that defines
them as a family of
molecules, is that they are
derived from the ent-
kaurene ring structure:
Conti…

 In 1958 a gibberellin (gibberellin A1) was
conclusively identified from a higher plant
(runner bean seeds, Phaseolus coccineus):
 As more and more gibberellins from fungal
and plant sources were characterized, they
were numbered as gibberellin AX (or
GAX),
where X is a number, in the order of their
discovery.
Conti…

C 20-Gas., e.g, GA12, GA27, GA53 etc.
 Others have only 19 (C19-GAs), having lost
one carbon to metabolism.
C 19 –Gas., e.g, GA1, GA3, GA20 etc.
Conti…

BIOSYNTHESIS AND METABOLISM
OF GIBBERELLIN

 Gibberellins constitute a large family of diterpene acids and are
synthesized by a branch of the terpenoid pathway.
 The elucidation of the gibberellin biosynthetic pathway would not have
been possible without the development of sensitive methods of
detection.
BIOSYNTHESIS AND METABOLISM OF GIBBERELLIN

 Systems of measurement using a biological response, called bioassays,
were originally important for detecting gibberellin-like activity in partly
purified extracts and for assessing the biological activity of known
gibberellins.
 The use of bioassays, however, has declined with the development of
highly sensitive physical techniques that allow precise identification and
quantification of specific gibberellins from small amounts of tissue
Gibberellins Are Measured via Highly Sensitive
Physical Techniques

 Gibberellins are tetracyclic diterpenoids
made up of 4 - isoprenoid units.
 Terpenoids are compounds made up of
five-carbon (isoprene) building blocks
Gibberellins Are Synthesized via the
Terpenoid Pathway in Three Stages
In plant GAs are biosynthesized in apical tissues and 3 main sites of
biosynthesis
1. Developing seeds and fruits,
2. The young leaves of developing apical buds and elongating shoots, and
3. The apical regions of roots.

 The gibberellin biosynthetic pathway can be divided into three stages,
each residing in a different cellular compartment.
(Hedden and Phillips 2000)
Conti…

Stage – 1 Production of terpenoid precursors and ent-kaurene in plastids
Isopentyl
Pyrophosph
ate (IPP) –
5C
Dimethyl
Allyl
Diphosphate
(DMAPP) –
5C
Isopentyl
Pyrophosph
ate (IPP) –
5C
Isopentyl
Pyrophosph
ate (IPP) –
5C
Geranyl Diphosphate (GPP)-10 C
Farnesyl Diphosphate (FPP)
FPP-15 C
GGPP-20 C
ENT
Copalyl
Diphosphate
Copalyl Diphosphate
Synthase (CPP)
ENT
Kaurene
Kaurene Synthase
PLASTID

Stage – 2 Oxidation reactions on the ER form GA12 and GA53
ENT
Kaurene
ENT Kaurenoic
acid
Kaurene Oxidase (KO)
Kaurene acid Oxidase
(KAO)
GA 12
ROUGH ENDOPLASMIC RETICULUM (RER)

Stage – 3 Formation in the cytosol of all other gibberellins from GA12 or GA53
GA 12 GA 53 GA44 GA19 GA20 GA1 GA8
GA 15 GA24 GA9 GA4 GA29
GA 12
13 – OH PATHWAY
NON 13 – OH PATHWAY
GA 13ox GA 20ox GA 20ox GA 20ox GA 3ox GA 2ox
GA 20ox GA 20ox GA 20ox GA 3ox GA 2ox
CYTOSOL

 The gibberellins of tall pea plants containing the homozygous Le allele
(wild type) were compared with dwarf plants having the same genetic
makeup, except containing the le allele (mutant).
 Le and le are the two alleles of the gene that regulates tallness in peas, the
genetic trait first investigated by Gregor Mendel in his pioneering study in
1866.
 We now know that tall peas contain much more bioactive GA1 than dwarf
peas have.
(Ingram et al. 1983)
GA1 Is the Biologically Active Gibberellin
Controlling Stem Growth

Endogenous GA1 Levels Are
Correlated with Tallness

 Shoots of gibberellin-deficient le dwarf peas are much shorter
than those of normal plants (internodes of 3 cm in mature dwarf
plants versus 15 cm in mature normal plants), the mutation is
“leaky” (i.e., the mutated gene produces a partially active
enzyme) and some endogenous GA1 remains to cause growth.
 Different le alleles give rise to peas differing in their height,
and the height of the plant has been correlated with the
amount of endogenous GA1.
Endogenous GA1 Levels Are Correlated
with Tallness
 Stem elongation corresponds closely to the level of
GA1. Here the GA1 content in peas with three
different alleles at the Le locus is plotted against
the internode elongation in plants with those
alleles. The allele le-2 is a more intense dwarfing
allele of Le than is the regular le-1 allele. There is
a close correlation between the GA level and
internode elongation. (After Ross et al. 1989.)

 There is also an extreme dwarf mutant of
pea that has even fewer gibberellins.
 This dwarf has the allele na (the wild-type
allele is Na), which completely blocks
gibberellin biosynthesis between ent-
kaurene and GA12-aldehyde.
 As a result, homozygous (nana) mutants,
which are almost completely free of
gibberellins, achieve a stature of only about
1 cm at maturity
(Reid and Howell 1995)
Endogenous GA1 Levels Are Correlated
with Tallness
The phenotype of 21-d-old seedlings of wild-
type NA (WL1769) and two independent mutants, na-
1 (WL1766) and na-2 (L81).

Endogenous GA1 Levels
Are Correlated with Tallness
Phenotypes and genotypes of peas that
differ in the gibberellin content of their
vegetative tissue. (All alleles are
homozygous).
Davies, 1995

nana plants
GA 3β-
hydroxylase
(Le)
GA20 – GA1
Conti…

Conti…
nana
naLe
Dwarf
le plant
tall
GA1 is the biologically active gibberellin that
regulates tallness in peas
Ingram et al. 1986; Davies 1995
nana shoot tip can convert the GA20 from the
dwarf into GA1.

GIBBERELLINS TRANSPORT IN PLANTS

 Gibberelins have been found from both phloem and xylem exudates from a
variety of plants. Unlike auxins, the transport of gibberellins in plants is non-
polar.
 It is believe that gibberellins are translocated through phloem according to a
flow pattern which is similar to those of carbohydrates and other organic
solutes.
 Gibberellins are not translocated in plant as free molecules but probably in their
bound form as gibberellin-glycosides.
 The movement of gibberellins from scutellum to the cells of the aleurone layer
in the germinating cereal seeds is well established.
GIBBERELLINS TRANSPORT IN PLANTS

 Seed germination may
require gibberellins for one
of several possible steps:
 The activation of
vegetative growth of the
embryo, the weakening of
a growth-constraining
endosperm layer
surrounding the embryo,
and the mobilization of
stored food reserves of the
endosperm.
Conti…
 Gibberellin application also stimulates the production of numerous hydrolases, notably
α-amylase, by the aleurone layers of germinating cereal grains.

 The highest levels of gibberellins are found in immature seeds and
developing fruits. However, because the gibberellin level normally
decreases to ZERO in mature seeds, there is no evidence that seedlings
obtain any active gibberellins from their seeds.
Gibberellins Are Biosynthesized in Apical
Tissues

 Work with pea seedlings indicates that the gibberellin biosynthetic
enzymes and GA3ox are specifically localized in young, actively
growing buds, leaves, and upper internodes.
 In Arabidopsis, GA20ox is expressed primarily in the apical bud and
young leaves, which thus appear to be the principal sites of gibberellin
synthesis.
Elliott et al. 2001
Conti…

 The gibberellins that are synthesized in the shoot can be transported to
the rest of the plant via the phloem.
 Intermediates of gibberellin biosynthesis may also be translocated in the
phloem.
 Indeed, the initial steps of gibberellin biosynthesis may occur in one
tissue, and metabolism to active gibberellins in another.
 Gibberellins also have been identified in root exudates and root
extracts, suggesting that roots can also synthesize gibberellins and
transport them to the shoot via the xylem.
Conti…

 FIGURE
Gibberellin is synthesized mainly in the shoot apex and
in young developing leaves. This false color image
shows light emitted by transgenic Arabidopsis plants
expressing the firefly luciferase coding sequence
coupled to the GA20ox gene promoter. The emitted light
was recorded by a CCD camera after the rosette was
sprayed with the substrate luciferin. The image was then
color-coded for intensity and superimposed on a
photograph of the same plant. The red and yellow
regions correspond to the highest light intensity.
(Courtesy of Jeremy P. Coles, Andrew L. Phillips, and
Peter Hedden, IACR-Long Ashton Research Station.)
Conti…

 The time courses of the changes in radioactive content of hypocotyl and epicotyl.
 The radioactivity in the hypocotyl was highest at 50 min, and was higher under CL-DT and DT-DT
than under CL-CL condition for both GA1, and GA20 applications.
 When GA20 was applied to the cotyledon of seedlings grown under CL-CL, radioactivty was
observed in the epicotyl from 50 min to 10 h after application.
 However, little radioactivity was observed in the epicotyl when GA1, was applied to cotyledon and
undetectable at 50 min.
 The translocation of both GA1, and GA20 from the cotyledon to the hypocotyl was greater under DT
condition than under CL after GAs application.
 In contrast, the translocation of GA20 from the cotyledon to the epicotyl was promoted by CL
conditions after GA application.
(Young-Yell Yang et al., 1996)
Translocation patterns of labeled GAs from the
cotyledon to hypocotyl and epicotyl

Table: Distribution of radioactivity in hypocotyl and epicotyl
at 50 min, 3, 10, 24 and 48hr after GA application to the
cotyledon

 The height of ‘w106’ was significant shorter
than that of ‘CG’ (Fig. a).
 Therefore, we conducted a microscopic
observation of shoots of the ‘CG’ and
‘w106’ plants using paraffin sectioning. The
cell sizes in transverse sections were not
obviously different between the ‘CG’ and
‘w106’ plants (Fig. b).
 However, the cell lengths in longitudinal
sections were obviously shorter in ‘w106’
than in ‘CG’ plants (Fig. c). Thus, the
defective cell elongation appears to be the
main cause for the reduced shoots and dwarf
architecture in watermelon.
Phenotypic and genetic analyses
Yuyan Sun et al., 2020
Case Study

Phenotypic and genetic analyses

ENVIRONMENTAL CONDITIONS CAN ALTER
THE TRANSCRIPTION OF GIBBERELLIN
BIOSYNTHESIS GENES

 Gibberellins play an important role in mediating the effects of
environmental stimuli on plant development.
 Environmental factors such as photoperiod and temperature can alter the
levels of active gibberellins by affecting gene transcription for specific
steps in the biosynthetic pathway.
Yamaguchi and Kamiya 2000
ENVIRONMENTAL CONDITIONS CAN ALTER THE TRANSCRIPTION OF
GIBBERELLIN BIOSYNTHESIS GENES

 The presence of light has many profound effects. Some seeds germinate
only in the light, and in such cases gibberellin application can stimulate
germination in darkness.
 The promotion of germination by light has been shown to be due to
increases in GA1 levels resulting from a light-induced increase in the
transcription of the gene for GA3ox, which converts GA20 to GA1
(Toyomasu et al. 1998).
 This effect shows red/far-red photoreversibility and is mediated by
phytochrome
Light regulation of GA1 biosynthesis

Conti…
 When a plant grows in the light,
the rate of extension slows
down through regulation by
changes in hormone levels and
sensitivity. (A) When dark-
grown pea seedlings are
transferred to light, GA1 level
drops rapidly because of
metabolism of GA1, but then
increases to a higher level,
similar to that of light-grown
plants, over the next 4 days.

 (B) To investigate the GA1 response in
various light regimes, 10 mg of GA1
was applied to the internode of GA-
deficient na plants in darkness, 1 day
after the start of the light, or 6 days of
continuous light, and growth in the next
24 hours was measured. The results
show that the gibberellin sensitivity of
pea seedlings falls rapidly upon transfer
from darkness to light, so the elongation
rate of plants in the light is lower than in
the dark, even though their total GA1
content is higher.
Conti…
After O’Neill et al. 2000.

 Potato tuberization is another process regulated by
photoperiod (Figure A). Tubers form on wild potatoes
only in short days (although the requirement for short
days has been bred out of many cultivated varieties),
and this tuberization can be blocked by applications of
gibberellin. The transcription of GA20ox was found to
fluctuate during the light–dark cycle, leading to lower
levels of GA1 in short days. Potato plants
overexpressing the GA20ox gene showed delayed
tuberization, whereas transformation with the antisense
gene for GA20ox promoted tuberization, demonstrating
the importance of the transcription of this gene in the
regulation of potato tuberization.
Carrera et al. 2000
Photoperiod control of tuber formation
Figure A: Tuberization of potatoes is promoted
by short days. Potato (Solanum tuberosum spp.
Andigena) plants were grown under either long
days or short days. The formation of tubers in
short days is associated with a decline in GA1
levels.
Courtesy of S. Jackson.

 Many plants respond to application of GA
by a marked increase in stem length; the
effect is primarily of internode elongation.
 Applied gibberellin promotes internodal
elongation in a wide range of species,
A. Elongation of intact stems
Illustration of internodal elongation
in dwarf varieties after treatment
with GA

 Gibberellin increases both cell elongation and cell division, as evidenced
by increases in cell length and cell number in response to applications of
gibberellin.
 For example, internodes of tall peas have more cells than those of dwarf
peas, and the cells are longer. Mitosis increases markedly in the subapical
region of the meristem of rosette long-day plants after treatment with
gibberellin.
After Sachs 1965
Cell Elongation and Cell Division

 Continuous recording of the growth of the upper internode
of deep-water rice in the presence or absence of exogenous
GA3.
 The control internode elongates at a constant rate after an
initial growth burst during the first 2 hours after excision of
the section.
 Addition of GA after 3 hours induced a sharp increase in the
growth rate after a 40-minute lag period (upper curve).
 The difference in the initial growth rates of the two
treatments is not significant here, but reflects slight
variation in experimental materials.
 The inset shows the internode section of the rice stem used
in the experiment. The intercalary meristem just above the
node responds to GA.
(After Sauter and Kende 1992.)
Conti…

 However, the most dramatic stimulations are
seen in dwarf and rosette species, as well as
members of the grass family.
 Exogenous GA3 causes such extreme stem
elongation in dwarf plants that they resemble
the tallest varieties of the same species.
 Accompanying this effect are a decrease in
stem thickness, a decrease in leaf size, and a
pale green color of the leaves.
 It appears that dwarfness of such varieties is
due to internal deficiency of gibberellins.
Conti…
Dwarf pea plants without (left) or with GA
(right) treatment (5 μg) for one week.

1. GAI (Gibberellin insenstive dwarfs mutants)
2. RGA (Gibberellin deficiency reversion mutants)
3. SPY (Spindle or slender mutant)
 GAI + RGA – amino terminal (protein) = DELLA
(DELLA Repressors)
Repressors

 Functional DELLA repressors have been found in several crop plants that have dwarfing
mutations, analogous to gai-1, in the genes encoding these proteins.
 Most notable are the rht (reduced height) mutations of wheat that have been in use in
agriculture for 30 years.
 These alleles encode gibberellin response modulators that lack gibberellin
responsiveness, leading to dwarfness (Peng et al. 1999; Silverstone and Sun 2000).
 Cereal dwarfs such as these are very important as the foundations of the green
revolution that enabled large increases in yield to be obtained.
 Normal cereals grow too tall when close together in a field, especially with high levels
of fertilizer. The result is that plants fall down (lodge), and the yield decreases
concomitantly. The use of these stiff-strawed dwarf varieties that resist lodging enables
high yields.
DELLA Repressors Have Been Identified
in Crop Plants

The Negative Regulator SPINDLY Is an
Enzyme That Alters Protein Activity
 “Slender mutants” resemble wild-type plants that have been treated with gibberellin repeatedly.
They exhibit elongated internodes, parthenocarpic (seed-free) fruit growth (in dicots), and poor
pollen production. Slender mutants are rare compared to dwarf mutants.

B. Mobilization of
Endosperm food
reserve

 Certain light sensitive seeds e.g., lettuce and tobacco show poor
germination in dark.
 Germination starts vigorously if these seeds are exposed to light or red
light.
 This requirement of light is overcome if the seeds are treated with
gibberellic acid in dark.
Seed Germination & Dormancy

 Bolting is a survival mechanism
in a plant.
 If the environmental conditions
necessary for the growth of the
plant are fluctuating or are
becoming stressful for the
survival of the plant, it will try to
produce the next generation
(seeds) as quickly as possible.
 Essentially, it is the premature
production of a flowering stem
(or stems) on a plant before it can
be harvested.
Bolting
GA induced bolting in Arabidopsis

 Gibberellin can substitute for the long day or cold
requirement for flowering in many plants.
 In plants where flowers are unisexual rather than
hermaphroditic, floral sex determination is genetically
regulated.
 However, it is also influenced by environmental factors,
such as photoperiod and nutritional status, and these
environmental effects may be mediated by gibberellin.
 In maize, for example, the staminate flowers (male) are
restricted to the tassel, and the pistillate flowers (female)
are contained in the ear.
 Exposure to short days and cool nights increases the
endogenous gibberellin levels in the tassels 100-fold and
simultaneously causes feminization of the tassel flowers.
 Application of exogenous gibberellic acid to the tassels can
also induce pistillate flowers.
Gibberellins Influence Floral Initiation

 Applications of gibberellins can cause fruit set (the initiation of fruit
growth following pollination) and growth of some fruits, in cases where
auxin may have no effect.
 For example, stimulation of fruit set by gibberellin has been observed in
apple (Malus sylvestris).
Gibberellins Promote Fruit Set

Case Study
Manabu Watanabe et al., 2008

Effects of single and combined treatment of plant growth regulators on
the fruit set and shape of parthenocarpic apple fruits
• The fruit retention rate in ‘Ohrin’ decreased from 8 DAT in the
control, 2,4-DP-alone, and CPPU-alone treatments, and from 14
DAT in the GA3-alone and GA3-combined treatments (Fig. 2A).
• The wave pattern of fruit drop in ‘Ohrin’ was bimodal in control,
2,4-D Palone, CPPU-alone and GA3 + 2,4-DP treatments, and was
uni-modal in the GA3-alone and GA3 + 2,4-DP + CPPU
treatments.
• Regarding ‘Fuji’, the control, 2,4-DPalone, and CPPU-alone
treatment showed a fruit retention rate decrease from 6 DAT (Fig.
2B).
• The fruit retention rate of GA3-alone and GA3+2,4-DP treatments
decreased from 21 DAT; that of CPPU-combined treatments
decreased from 28 DAT. ‘Fuji’ showed one peak period of fruit
drop, except for the control.

 A major use of gibberellins is to
increase the stalk length of seedless
grapes.
 Because of the shortness of the
individual fruit stalks, bunches of
seedless grapes are too compact and
the growth of the berries is restricted.
 Gibberellin stimulates the stalks to
grow longer, thereby allowing the
grapes to grow larger by alleviating
compaction, and it promotes
elongation of the fruit.
Conti...
Gibberellin induces growth in Thompson’s seedless grapes. The bunch on the left
is an untreated control. The bunch on the right was sprayed with gibberellin
during fruit development. (Sylvan Wittwer)

GA application for increasing fruit size
Variety: Thomson’s Seedless
Every 1 – 1.5 weeks application of GA.
GA – 3 times for increasing fruit size @ 3, 2, 2 gm
Cuttings @ Oct
Harvesting @ March Farmer: Naveen Verma (2022)

 Amin HASSANKHAH , Majid RAHEMI , Mohamad Reza MOZAFARI , Kourosh VAHDATI. (2018). Flower Development in Walnut: Altering
the Flowering Pattern by Gibberellic Acid Application. Not Bot Horti Agrobo, 2018, 46(2):700-706. DOI:10.15835/nbha46211183
 Bethke, P. C., Schuurink, R., and Jones, R. L. (1997) Hormonal signalling in cereal aleurone. J. Exp. Bot. 48: 1337–1356.
 Carrera, E., Bou, J., Garcia-Martinez, J. L., and Prat, S. (2000) Changes in GA 20-oxidase gene expression strongly affect stem length, tuber
induction and tuber yield of potato plants. Plant J. 22: 247–256
 Davies, P. J. (1995) The plant hormones: Their nature, occurrence, and functions. In Plant Hormones: Physiology, Biochemistry and Molecular
Biology, P. J. Davies, ed., Kluwer, Dordrecht, Netherlands, pp. 1–12.
 Elliott, R. C., Ross, J. J., Smith, J. J., and Lester, D. R. (2001) Feed-forward regulation of gibberellin deactivation in pea. J. Plant Growth Regul. 20:
87–94.
 G. A. Martínez, A. R. Chaves & M. C. Añón (1996). Effect of exogenous application of gibberellic acid on color change and phenylalanine
ammonia-lyase, chlorophyllase, and peroxidase activities during ripening of strawberry fruit (Fragaria x ananassa Duch.). Journal of Plant
Growth Regulation volume 15, Article number: 139.
 Haemyeong Jung, Seung Hee Jo, Won Yong Jung, Hyun Ji Park , Areum Lee, Jae Sun Moon, So Yoon Seong, Ju-Kon Kim, Youn-Sung Kim,* and
Hye Sun Cho. Gibberellin Promotes Bolting and Flowering via the Floral Integrators RsFT and RsSOC1-1 under Marginal Vernalization in
Radish(2020). 9, 594; doi:10.3390/plants9050594.
 Hedden, P., and Kamiya, Y. (1997) Gibberellin biosynthesis: Enzymes, genes and their regulation. Annu. Rev. Plant Physiol. Plant Mol. Biol. 48:
431–460.
 Ingram, T. J., Reid, J. B., Potts, W. C., and Murfet, I. C. (1983) Internode length in Pisum. IV The effect of the Le gene on gibberellin metabolism.
Physiol. Plant. 59: 607–616.
REFERENCE

 Manabu Watanabe1 *, Hideyuki Segawa1 , Masanobu Murakami1 , Satoru Sagawa1 and Sadao Komori2. (2008). Effects of Plant
Growth Regulators on Fruit Set and Fruit Shape of Parthenocarpic Apple Fruits. J. Japan. Soc. Hort. Sci. 77 (4): 350–357.
 O’Neill, D. P., Ross, J. J., and Reid, J. B. (2000) Changes in gibberellin A1 levels and response during de-etiolation of pea seedlings.
Plant Physiol. 124: 805–812.
 Reid, J. B., and Howell, S. H. (1995) Hormone mutants and plant development. In Plant Hormones: Physiology, Biochemistry and
Molecular Biology, P. J. Davies, ed., Kluwer, Dordrecht, Netherlands, pp. 448–485.
 Yamaguchi, S., and Kamiya, Y. (2000) Gibberellin biosynthesis: Its regulation by endogenous and environmental signals. Plant Cell
Physiol. 41: 251–257.
 Sauter, M., and Kende, H. (1992) Gibberellin-induced growth and regulation of the cell division cycle in deepwater rice. Planta 188:
362–368.
 Sachs, R. M. (1965) Stem elongation. Annu. Rev. Plant. Physiol. 16: 73–96.
 Young-Yell Yang', Isomaro Yamaguchi and Noboru Murofushi. 1996. Metabolism and Translocation of Gibberellins in the Seedlings of
Pharbitis nil (II). Photoperiodic Effects on Metabolism and Translocation of Gibberellins Applied to Cotyledons, Plant Cell Physiol.
37(1): 69-75.
 Zeevaart, J. A. D., Gage, D. A., and Talon, M. (1993) Gibberellin A1 is required for stem elongation in spinach. Proc. Natl. Acad. Sci.
USA 90: 7401–7405.

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Biosynthesis of gibberellins.pptx