1.
ROLE OF PLANT GROWTH
REGULATORS IN SEED
GERMINATION
SUBMITTED BY –
LOVELEEN KUMARI
M.Sc. Ag. Horti. Fruit Science Sem –III

2.
PLANT GROWTH REGULATORS
• Plant growth regulators may defined as either natural or synthetic compounds that are produced
endogenously or applied directly to a plant which modify plant physiological processes.
• Plant hormones – It is also called as “phytohormones”. Plant hormones are natural compounds
which are produced within the plants.
• PGRs also known as biostimulants or bioinhibitors that act inside plant cells to stimulate or
inhibit specific enzymes.
PLANT
GROWTH
REGULATORS
GROWTH
PROMOTERS
GROWTH
INHIBITORS
GROWTH
INHIBITORS &
PROMOTERS
• AUXIN
• CYTOKININ
• GIBBERELLIC ACID
• ABSCISIC ACID
(ABA)
• ETHYLENE

3.
NATURAL AND SYNTHETIC GROWTH REGULATORS
CLASS ENDOGENOUS HORMONE GROWTH REGULATORS
AUXIN Indole Acetic Acid IBA, NAA, 2-4-D
CYTOKININ Zeatin Kinetin, BA
GIBBERELLIN GA4,GA12,GA9 etc. GA3
ABSCISIC ACID Abscisic acid (ABA)
ETHYLENE Ethylene Ethephon, Ethrel

4.
SEED GERMINATION
• Seed germination may be defined as the fundamental process by which different plant species
grow from a single seed into a plant.
• Seed germination is a key stage during a plant’s life-cycle, and the germination process is
determined by various environmental factors, such as the availability of light, water and
oxygen, as well as the presence of endogenous phytohormones.

5.
PROCESS OF SEED GERMINATION
Sugars converted into energy
Proteins into amino acids
Starch converted to sugars
Alpha amylase & protease produced
GA in aleurone cells stimulates prod. of enzymes
GA travel to aleurone cells
Embryo releases GAs
Metabolic process increases
Imbibition

6.
PGRs in seed germination
• In the mechanism of seed germination, morphological and physiological changes occurs as a result there
is activation of embryo. Before germination, water is absorbed by the seed, which helps in elongation
and expansion of the seed embryo. When the radicle has emerged from the covering seed layers, the
process of seed germination is completed. (Hermann et al., 2007)
• According to Graeber et al. (2012), plant hormones can influence a variety of plant processes, including
seed germination and dormancy.
• Biochemical molecules called plant hormones, such as ABA, ethylene, gibberellins, auxin (IAA),
cytokinins, and brassinosteroids, regulate a variety of physiological and biochemical activities in plants.
Plants and soil microorganisms also contribute to the production of these interesting compounds.
(Finkelstein, 2004; Santner et al., 2009; Jimenez, 2005)

7.
ROLE OF PGRs IN SEED GERMINATION
1. AUXIN –
• Exogenous auxin treatment represses soybean seed germination by enhancing ABA biosynthesis, while impairing
GA biogenesis, and finally decreasing GA1/ABA and GA4/ABA ratios. Microscope observation showed that
auxin treatment delayed rupture of the soybean seed coat and radicle protrusion. (Shuai H, et al 2017)
• Auxin promotes dormancy and inhibits germination by enhancing ABA action, thereby adding another protective
level of control in the regulation of seed dormancy. (Liu X et al, 2013)
(Wang M, et al 2021)
Effect of sugar and PGRs on seed germination

8.
2. CYTOKININ –
In an experiment J. Van Staden et al ( 2010) monitored endogenous cytokinin levels during germination and early seedling
establishment in monocotyledons (Oats & Maize) and dicotyledons ( Lettuce & Lucerne).
• UPLC-ESI-MS/MS was used to identify endogenous cytokinin levels.
• Before radicle emergence, there was a slight rise in cytokinin levels after imbibition. Compounds found in the seeds
were –
Form of cytokinin Seeds
Cis-zeatin types (cZ) lettuce, lucerne and oats
Dihydrozeatin (DHZ) derivatives and Benzyladenine (BA) Maize
Seeds Compounds founded
1. Lettuce Increase in BA and various meta-topolins(mT) forms
2. Lucerne Increase in cZ- and Topolin-(mT)forms
3.Oats Increase in trans-zeatin (tz) forms

9.
• Due to an increase in cis-Zeatin, another transitory cytokinin peak was found after radicle emergence.
Different forms of cytokinin were identified in the seed after the radicle emergence i.e.-
Seeds of
plant
Compounds founded
1.Lettuce BA- and topolin-forms
2.Lucerne cZ- and topolin-forms
3. Oats BA- and isopentenyladenine—(iP) forms
4. Maize Large increase in cZ forms and smaller peaks in iP-,
tZ- and BA-forms
J Van Staden et al (2010)

10.
3. GIBBERELLIC ACID -
• Intake of water activates the hormone gibberellin, which then signals to transcribe the gene
encoding amylase, an enzyme that breaks down starches stored in the seed into simple sugars, and then
germination proceed .
• When water is absent, germination in this pathway is blocked by a hormone called abscisic acid (also
called ABA), which inhibits the activity of gibberellins. Thus gibberellins and abscisic acid act in opposition
in regulating the germination response.
• GA3 @500ppm solution enhances seed germination in aonla and ber.
• Dip treatment of GA for 12 hours before sowing, significantly enhances seed germination in papaya.
• GA enhances the germination of seeds by enhancing alpha-amylase enzyme that breaks down the complex
carbohydrates into simple sugars and provide energy to the growing embryo.(Bal and Gill, 2018)

11.
4. ABSCISIC ACID –
• Abscisic acid plays major role in seed maturation and maintaining seed dormancy under adverse climatic
conditions.
• ABA is antagonized by Gibberellins.
• ABA delays radicle expansion and weakens the endosperm..
ABA BIOSYNTHESIS THROUGH CAROTENOID PATHWAY

12.
5. ETHYLENE –
• Ethylene promotes germination of many species such as apple
(Malus domestica) and participates in the release from seed
dormancy.
• Ethylene plays a key role in dormancy release in numerous
species, the effective concentrations allowing the germination
of dormant seeds ranging between 0.1 and 200 μL/L.
• Induction of thermodormancy at high temperatures is
associated with a reduced ethylene production in chickpea
(Gallardo et al., 1991), sunflower (Corbineau et al., 1988), and
lettuce (Prusinski and Khan, 1990).
• Breaking of dormancy by various treatments (e.g., chilling,
GAs, NO, HCN) leads to an increase in ethylene production.
(Kepczynski and Kepczynska, 1997; Arc et al., 2013)
Corbineau F et al.,(2014)

13.
Phytohormones in the regulation of seed germination
Ali F et al., (2022)

14.
REFERENCES
• Ali, F., Qanmber, G., Li, F. and Wang, Z., 2022. Updated role of ABA in seed maturation, dormancy, and
germination. Journal of Advanced Research, 35, pp.199-214.
• Bal, J.S., 2020. Plant growth regulators in fruit science. (Ed. By J.S. Bal). Kalyani Publishers, New Delhi.
• Corbineau, F., Xia, Q., Bailly, C. and El-Maarouf-Bouteau, H., 2014. Ethylene, a key factor in the regulation of seed
dormancy. Frontiers in plant Science, 5, p.539.
• Hermann, K., Meinhard, J., Dobrev, P., Linkies, A., Pesek, B., Heß, B., Macháčková, I., Fischer, U. and Leubner-
Metzger, G., 2007. 1-Aminocyclopropane-1-carboxylic acid and abscisic acid during the germination of sugar beet
(Beta vulgaris L.): a comparative study of fruits and seeds. Journal of Experimental Botany, 58(11), pp.3047-3060.
• Liu, X., Zhang, H., Zhao, Y., Feng, Z., Li, Q., Yang, H.Q., Luan, S., Li, J. and He, Z.H., 2013. Auxin controls seed
dormancy through stimulation of abscisic acid signaling by inducing ARF-mediated ABI3 activation in
Arabidopsis. Proceedings of the National Academy of Sciences, 110(38), pp.15485-15490.
• Miransari, M. and Smith, D.L., 2014. Plant hormones and seed germination. Environmental and experimental
botany, 99, pp.110-121.
• Shuai, H., Meng, Y., Luo, X., Chen, F., Zhou, W., Dai, Y., Qi, Y., Du, J., Yang, F., Liu, J. and Yang, W., 2017.
Exogenous auxin represses soybean seed germination through decreasing the gibberellin/abscisic acid (GA/ABA)
ratio. Scientific Reports, 7(1), pp.1-11.
• Van Staden, J., Stirk, W.A., Novák, O. and Strnad, M., 2010. The role of cytokinins in seed germination. South
African Journal of Botany, 2(76), p.405.Wang, M., Le Gourrierec, J., Jiao, F., Demotes-Mainard, S., Perez-Garcia,
M.D., Ogé, L., Hamama, L., Crespel, L., Bertheloot, J., Chen, J. and Grappin, P., 2021. Convergence and divergence
of sugar and cytokinin signaling in plant development. International Journal of Molecular Sciences, 22(3), p.1282.

15.
THANK YOU