This document summarizes the roles of various plant hormones in reproductive growth and development. It discusses how auxin, gibberellins, cytokinin, ethylene, and vernalization influence processes such as flowering initiation, floral organ development, and seed production. Hormones integrate environmental and developmental signals and regulate gene expression and transcription factors that control transitions between phases of growth. For example, gibberellins and auxin promote flowering by activating floral integrator genes in leaves and meristems. Cytokinin influences meristem activity and organ size. Recent research has provided insight into hormonal regulation and communication between plant tissues as they coordinately control reproductive development.

1. MOLECULAR ASPECTS OF CONTROL OF
REPRODUCTIVE GROWTH AND DEVELOPMENT
Presented By,
Chavan Mahadeo Rajaram
ADPM/15/2422
Genetics & Plant Breeding

2. • Hormones are chemical signals that integrate
internal developmental and external
environmental inputs and transform them into
appropriate responses.
• The responses require specific receptors and a
signal-transduction pathway to coordinate
downstream responses
Reception Transduction Respones .

3. Role of auxin
• Auxin is an essential hormone that has been
implicated in many aspects of plant growth and
development (Woodward and Bartel 2005).
• Auxin plays role in the initiation of flowering and
development of reproductive organs.
• A number of plant mutants have been described
that affect flowering . In maize, one example is bif2
barren inflorescence.

4. • A link between auxin and flower development
was first established when the auxin transport
mutant pin1 was isolated and characterized
(Okada et al. 1991; Galweiler et al. 1998).
• Transcription factors responsible for floral
meristem and floral organ develpoment.
• Therefore, flower development provides a great
system to analyze the mechanisms by which
auxin regulates plant organogenesis and pattern
formation.

5. SIGNAL TRANSDUCTION

7. Gibberrelin in flower initiation
• The ability of gibberellins (GAs) to promote pollen formation
and induction of flowering.
• Gibberellins (GAs) function not only to promote the growth of
plant organs, but also to induce phase transitions during
development.
• GAs mediate the photoperiodic stimulus to flowering in LD
plant.
• In Arabidopsis thaliana, a facultative LD and cold-responsive
species, GA contributes to one of four interacting pathways
for floral induction

8. • For photoperiod-enhanced GA biosynthesis in leaves ,
through up-regulation of GA 20-oxidase gene expression, a
signals from leaves to apices in response to LD has been
transmitted for flowering.
• In Arabidopsis thaliana, as one of four quantitative floral
pathways, in SD, in the absence of the photoperiod
flowering pathway, the GA pathway assumes a major role
and becomes obligatory.
• Gibberellins promote flowering in Arabidopsis through the
activation of genes encoding the floral integrators
SUPPRESSOR OF OVEREXPRESSION OF CONSTANS 1 (SOC1),
LEAFY (LFY), and FLOWERING LOCUS T (FT) in the
inflorescence and floral meristems, and in leaves,
respectively.

9. • These genes encode proteins that activate the floral
meristem identity (FMI) geneS
APETALA1 (AP1), APETALA2 (AP2),FRUITFULL (FUL), C
AULIFLOWER (CAL) and LFY, which convert the
vegetative meristem to a floral fate.
• GA signalling is not required for floral organ
specification, it is essential for the normal growth
and development of these organs.

11. GAIN vernalisation
 The cooling of seed
during germination in
order to accelerate
flowering when it is
planted.
 Cold treatment
activates VER203 gene
expression.
 GA also induces VER203
expression thus GA can
partially substitute cold
treatment to initiate
flowering in plants that
require cold treatment.

12. ROLE OF CYTOKININ
 Cytokinin regulates the activity of reproductive
meristems, flower organ size, ovule formation, and
thus seed yield.
 The cytokinin status of the meristem depends on
different factors, including metabolic degradation of
the hormone, which is catalyzed by cytokinin
oxidase/dehydrogenase (CKX) enzymes.
 CKX3 and CKX5 regulate the activity of the
reproductive meristems of Arabidopsis thaliana.

13.  CKX3 is expressed in the central WUSCHEL (WUS) domain,
while CKX5 shows a broader meristematic expression. ckx3
ckx5 double mutants form larger inflorescence and floral
meristems.
 Mutation of a negative regulator gene of cytokinin signaling,
ARABIDOPSIS HISTIDINE PHOSPHOTRANSFER PROTEIN 6,
which is expressed at the meristem flanks, caused a further
action.

14. ROLE OF ETHYLENE
The gaseous hormone which helps for fruit
ripening, floral development and sex
expression.
Ethylene (ET) is a notable signaling molecule
in higher plants.
 In the year 1993 the ET receptor gene, ETR1,
was identified; this ETR1 receptor protein
being the first plant hormone receptor to be
isolated.

17. FLORIGEN
• Florigen (or flowering hormone) is the hypothesized hormone-
like molecule responsible for controlling triggering flowering
in plants.
• Florigen is produced in the leaves, and acts in the shoot apical
meristem of buds and growing tips.
• Research into florigen is predominately centred on the model
organism and long day plant, Arabidopsis thaliana.
• Mode of action :
1. Photoperiod-regulated initiation
2.Signal translocation via the phloem
3. Induction of flowering at the shoot apical
meristem.

18. • The signal initiation - messenger RNA (mRNA) coding a
transcription factor called CONSTANS (CO).
mRNA is then translated into CO protein.
• CO protein promotes transcription of another gene
called Flowering Locus T (FT)
• FT protein interacts with a transcription factor (FD
protein) to activate floral identity genes.
• Increased expression of at least one direct target gene,
APETALA 1 (AP1), along with other targets, such as SOC1
and several SPL genes, which are targeted by a microRNA

21. Case study….
• Integrating hormones into the floral-transition
pathway of Arabidopsis thaliana
SETH J. DAVIs

22. CONCLUSION
 Physiological and genetic approaches have revealed that
different organ parts of Arabidopsis are important for the
transition to flowering.
 Thus, these different tissues/organs must be able to communicate in
order to coordinately regulate floral transition of the plant. Hormonal
signals must partially mediate this process.
 Recent studies in Arabidopsis have successfully started to dissect the leaf-
to-shoot apex relation and identified florigen and two other compounds
that are transported from leaves to the apex before the floral transition
(Zeevaart 2006, 2008).
 It can be argued that one hormonal compound is the phytohormone GA,
which could be a component of the florigenic activity under noninductive
photoperiodic conditions, thus acting redundantly to the protein factor FT.
 Furthermore, the role of diverse phytohormones needs to be coherently
integrated, in a full context of signal convergence.

23. Reference
• Bartrina , Otto E, Strnad M, Werner T, Schmülling T.(2011) Cytokinin regulates the
activity of reproductive meristems, flower organ size, ovule formation, and thus
seed yield in Arabidopsis thaliana.
• Francisco De la Torre, María del Carmen Rodríguez-Gacio and Angel J
Matilla(2006). How Ethylene Works in the Reproductive Organs of Higher Plants.
• Jean-Michel Davière and Patrick Achard.(2013). Gibberellin signaling in plants.
Development at a glance
• Youfa Cheng and Yunde Zhao. (2007). A Role for Auxin in Flower Development.
Journal of Integrative Plant Biology , 49 (1): 99−104.
• WOUT BOERJAN, BART DEN BOER and MARC VAN MONTAGU. (1992). Molecular genetic
approaches to plant development. International journal of biology.36 : 59-66.
• Peter hedden (2008). Gibberellin as a factor in floral biology network. Oxford journal of
botany
• Book.goggle.co.in
• Wikipedia.
• You tube
• www.ncbi.co.insss

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