Abiotic stress related plant growth hormones. Abscissic acid as a signalling molecule.  Cytokinine is a molecule which is having negative control. Effect of abscissic acid & cytokinine on stomatal behaviour

1. ABIOTIC STRESS RELATED PLANT GROWTH
HORMONES.
ABSCISSIC ACID AS A SIGNALLING
MOLECULE.
CYTOKININE IS A MOLECULE WHICH IS
HAVING NEGATIVE CONTROL.
EFFECT OF ABSCISSIC ACID &
CYTOKININE ON STOMATAL BEHAVIOUR
Sumeena K J
Dept.SSAC
2018-11-109

2. ABIOTIC STRESS RELATED PLANT GROWTH
HORMONES
 Plant tries to manage abiotic stresses with the help of
phytohormones, often called growth regulators.
 They are chemical messengers
 They regulate tissue growth and differentiation,
determining when plants grow and mature.
 Plant growth regulators such as Abscisic acid,
ethylene, and Jasmonic acid are essentials in the
abiotic stress plant response.

3.  Plants can detect unfavorable environmental conditions
through hormones.
 Biosynthesis of phytohormones by the plants equips
them with a mechanism to adapt themselves according
to the prevailing situations.
 Abscisic acid help the plant to confront drought and
salinity stress,
 ethylene helps the plants in drought, over-watering, cold,
and salinity.

4.  Jasmonic acid aids plant to recover from
mechanical injuries and drought stress.
 Abiotic stress like water deficit, salinity, and heat
triggers production of enzymes depending upon the
genetic makeup of the plants, to produce the plant
growth regulators that may ultimately help them to
show resilience against stress or mitigation.

5. WHY IS ABSCISIC ACID ALSO KNOWN AS STRESS
HORMONE?
 It increases the tolerance of plants toward various
stresses.
 Induces the closure of the stomata during water stress.
 Promotes seed dormancy and ensures seed germination
during favorable conditions.
 It helps seeds withstand desiccation.
 It also helps in inducing dormancy in plants at the end of
the growing season and promotes abscission of leaves,
fruits, and flowers.

6. ABA BIOSYNTHESIS
 ABA level is known to induce under stress condition,
which is mainly due to the induction of genes for
enzymes responsible for ABA biosynthesis
 The abiotic stress-induced activation of many ABA
biosynthetic genes such as zeaxanthin oxidase (ZEP),
9-cis-epoxycarotenoid dioxygenase (NCED), ABA-
aldehyde oxidase (AAO) and molybdenum cofactor
sulphurase (MCSU) appeared to be regulated through
calcium-dependent phosphorylation pathway

7. ABA SIGNALING
 It is a key endogenous messenger in plants.
 3 core components of ABA signaling;
1. Pyrabactin resistance (PYR)/pyrabactin resistance-
like (PYL)/regulatory component of ABA receptors
(RCAR),
2. Protein phosphatase 2C (PP2C: acts as negative
regulators) and
3. (Sucrose non-fermenting) SNF1-related protein
kinase 2 (SnRK2: acts as positive regulators).

8.  In the presence of ABA, PYR/PYL/RCAR-PP2C complex
formation occurs.
 leads to inhibition of PP2C activity, which allows the
activation of SnRK2.
 Activated SnRK2 then phosphorylates downstream
substrate proteins such as transcription factors, and thus
facilitating transcription of ABA-responsive genes

9. MAJOR ABA SIGNALING PATHWAY IN PLANTS WITH
AND WITHOUT ABA PRESENCE.

10. ABA SIGNALLING DURING SEED DORMANCY

11. ABA SIGNALLING DURING SEED MATURATION

12. EFFECT OF ABSCISSIC ACID ON STOMATAL
BEHAVIOUR
 The hormone ABA triggers a signalling cascade in
guard cells
 Closing of stomata is mediated by turgor reduction
in guard cells, which is caused by efflux of K+
anions from guard cells.
 Inhibition of opening of through blocking K+ and H+
channels

13. ABA-INDUCED STOMATAL CLOSING

14. ABA- INHIBITS STOMATAL OPENING

15. EFFECT OF CYTOKININE ON STOMATAL BEHAVIOUR
 Cytokinins and auxins are known to antagonize
the effects of abscisic acid (ABA) and to affect
ethylene biosynthesis.
 As ethylene has an antagonistic effect on ABA-
induced stomatal closure, the possibility that the
antagonistic effects of these phytohormones on
ABA were mediated through ethylene biosynthesis
was investigated

16.  Both the cytokinin, 6-benzyladenine (BA), and the
auxin, 1-naphthaleneacetic acid (NAA),
antagonized ABA-induced stomatal closure in a
manner similar to that following application of the
ethylene precursor, 1-aminocyclopropane-1-
carboxylic acid (ACC).
 However, these effects were negated when
ethylene signalling, perception, or biosynthesis
were blocked. As stomatal aperture is regulated by
changes in guard cell volume, ABA application was
found to reduce the volume of the guard cell
protoplasts (GCP)

17.  It was found that BA, NAA, or ACC application
compensated perfectly for the reduction in GCP
volume by ABA application in WT plants. The above
observations suggest that cytokinins and auxins
inhibit ABA-induced stomatal closure through the
modulation of ethylene biosynthesis, and that
ethylene inhibits the ABA-induced reduction of
osmotic pressure in the guard cells.

18. CYTOKININ- AND AUXIN-INDUCED STOMATAL
OPENING INVOLVES A DECREASE IN LEVELS OF
HYDROGEN PEROXIDE IN GUARD CELLS OF VICIA
FABA
 cytokinins and auxins reduced the levels of H2O2 in
guard cells and induced stomatal opening in
darkness

19. CYTOKININ OVERPRODUCTION HAS BEEN
IMPLICATED IN GENETIC TUMORS
 In some interspecific hybrid Nicotiana tabacum ,
progeny that tend to form spontaneous tumors called
genetic tumors (Smith 1988).
 Genetic tumors form spontaneously in the absence of
any external inducing agent.
 The tumors are composed of masses of rapidly
proliferating cells in regions of the plant that ordinarily
would contain few dividing cells.

20.  Nicotiana hybrids that produce genetic tumors have
abnormally high levels of both auxin and cytokinins.
 The cytokinin levels in tumor-prone hybrids are five
to six times higher than those found in either
parent.

21. THANK YOU…