PROLINE AND GABA ACT AS ANTIOXIDANT IN PLANTS UNDER STRESS.

2. PROLINE
GAMMMA AMINO BUTYRIC ACID
(GABA)
STRUCTURE

3. PROLINE
 Alpha amino acid.
 Involves in protein synthesis.
 Cellular homeostasis.
 Can act as signaling molecule to modulate
mitochondrial functions.
 Influnces cell proliferation.
 Triggers specific gene expression.

4. REACTIVE OXYGEN SPECIES
(ROS)
 Aerobic metabolism constantly generates ROS which are
confined to the different plant cellular compartments, like the
chloroplast, mitochondria and peroxisomes.
 The major members of the ROS family include free radicals
like O•−
2, OH• and non-radicals like H2O2 and 1O2.
 Act as secondary messengers.
 Also induce oxidative damages under environmental stress
conditions.
 The cellular damages are manifested in the form of
degradation of biomolecules.
 Estimates show that only 1–2% of the O2 consumption by plant tissues,
leads to the formation of ROS.

5. FACTORS RESPONSIBLE FOR
GENERATION OF ROS
REF: Kaushik Das et al. Reactive oxygen species (ROS) and response of antioxidants as ROS-scavengers during
environmental stress in plants, Frontiers in Environmental Science, 2014, 2: 53

6. DIFFERENT MEMBERS OF THE ROS
FAMILY AND ATTRIBUTES
REF: Kaushik Das et al. Reactive oxygen species (ROS) and response of antioxidants as ROS-scavengers during
environmental stress in plants, Frontiers in Environmental Science, 2014, 2: 53

7. VARIOUS TARGETS OF ROS
REF: Kaushik Das et al. Reactive oxygen species (ROS) and response of antioxidants as ROS-scavengers during
environmental stress in plants, Frontiers in Environmental Science, 2014, 2: 53

8. To ensure survival, plants have
developed efficient antioxidant
machinery having two arms:
1. Enzymatic antioxidants
2. Non enzymatic antioxidants

9. ENZYMATIC AND NON -
ENZYMATIC ANTIOXIDANT
REF: Kaushik Das et al. Reactive oxygen species (ROS) and response of antioxidants as ROS-scavengers during
environmental stress in plants, Frontiers in Environmental Science, 2014, 2: 53
Non-enzymatic antioxidants

10. PLANT STRESS
Plant stress has been defined by Lichtenthaler
(1996) as any unfavorable environmental
conditions that alter plant growth, development
and metabolism, and even may lead to plant
death.
Salt and soil drought conditions are major
abiotic stress factors that limits crop
productivity.

12. GLUTAMATE
GLUTAMATE-
SEMIALDEHYDE(GSA
)
PYRROLINE-5-
CARBOXYLATE(P5
C)
PROLINE
PYRROLINE-5-
CARBOXYLATE
SYNTHETASE(P5C
S)
SPONTANEOUSE
PYRROLINE-
5-
CARBOXYLA
TE
REDUCTASE(
P5C
REDUCTASE) PYRROLINE-5-
CARBOXYLATE(P5C)
GLUTAMATE
PROLINE
DEHYDROGENASE(
PDH)
PROLINE
OXIDASE
PYRROLINE-5-
CARBOXYLATE
DEHYDROGENASE
(P5CDH)
SYNTHESIS AND DEGRADATION OF
PROLINE

13. PROLINE METABOLISM IN HIGHER
PLANTS
REF: Laszlo Szabados et al. Proline: a multifunctional amino acid, Trends in Plant Science, 2009, 15: 89-97

14. LOCALISATION OF ENZYMES
 P5CS1 accumulates in chloroplast under salt or osmotic
stress.
 P5CS2 predominantly localised in the cytosol.
 P5CR protein and activity detected in both cytosol and
chloroplast.
 PDH and P5CDH are mitochondrial enzymes that use
FAD and NAD+ as electron acceptors and generate FADH2
and NADH respectively, delivering elctrons for mitochondrial
respiration.
 When PDH activity is limited, the P5C-proline cycle can
transfer more electrons to the mitochondrial ETC and
generate reactive oxygen species (ROS)

15. MULTIPLE FUNCTIONS OF PROLINE
IN PLANTS
REF: Laszlo Szabados et al. Proline: a multifunctional amino acid, Trends in Plant Science, 2009, 15: 89-97

16. PROLINE AS ANTIOXIDANT
 Proline has the ROS scavenging activity by which it
protect the cells from oxidative damage.
 Proline treatment can diminish ROS levels in fungi
and yeast, thus preventing programmed cell death, and
can reduce lipid peroxidation in alga cells exposed to
heavy metals.
 Proline pretreatment also alleviated mercuric toxicity
in rice through scavenging ROS, such as H2O2
(hydrogen peroxide).

17. PROLINE AS ANTIOXIDANT AND
PERHAPS A PROTECTANT
The damaging effects of singlet oxygen and hydroxyl
radicals on photosystem 2 (PS2) can be reduced by
proline in isolated thylakoid membranes.
 As an alternative to direct ROS scavenging feature,
proline can protect and stabilise proteins and perhaps
ROS scavenging enzymes and activate alternative
detoxification pathways.
 Proline function as a molecular chaperone to protect
protein integrity and enhance the activities of different
enzymes. E.g. ribonucleases, proteases, nitrate
reductase, lactate dehydrogenase.

18. GAMMA AMINO BUTYRIC ACID
(GABA)
 NON PROTEINOGENIC AMINO ACID
 INHIBITORY NEUROTRANSMITTER IN CNS
 ALSO EXPRESSED IN NON- NEURAL CELLS
 DEFENCE AGAINST STRESS IN PLANTS
 REGULATOR OF FLIGHT OR FIGHT STRESS RESPONSE
 MOSTLY FOUND AS ZWITTER ION i.e CARBOXYL GROUP
DEPROTONATED AND AMINO GROUP PROTONATED
 BIOACTIVE CONSTITUENT OF FRUITS, VEGETABLES AND
CEREALS
 CELL SIGNALING IN PLANTS

19. BIOSYNTHESIS OF GABA
GABA shunt reactions are responsible for the synthesis, conservation and
metabolism of GABA. GABA-T, GABA α-oxoglutarate transaminase; GAD, glutamic
acid decarboxylase; SSADH, succinic semialdehyde dehydrogenase

20. GABA SHUNT PATHWAY
• In cytosol, glutamate
decarboxylase(GAD)
catalyses glutamate to
GABA.
•GABA is transported from
cytosol to mitochondria and
forms succinate
semialdehyde(SSA),
catalysed by 2-oxyglutarate-
dependent GABA
transaminase(GABA-T).
•SSA is converted to
succinate by SSA
dehydrogenase(SSADH).
•Succinate enters to TCA
cycle
REF: Barry J. Shelp et al. Compartmentation of GABA metabolism raises intriguing questions, Trends in Plant
Science, 2012, 17: 57-59

21. REDOX HOMEOSTASIS BY GABA
During stress conditions GABA levels
increase because stress is generally
associated with elevated ratios of NADH to
NAD+ and NADPH to NADP+ , and
frequently with cytosolic acidosis (e.g.
hypoxia), the glyoxylate reductase (GLYRs),
like glutamate decarboxylate (GAD), would
be expected to function efficiently during
stress.

22. PLANT UNDER STRESS
SIGNAL TRANSDUCTION PATHWAY
INCREASED CYTOSOLIC CALCIUM
CALCIUM /CALMODULIN DEPENDENT GLUTAMATE
DECARBOXYLASE ACTIVITY
ACTIVATION
GABA SYNTHESIS
INCREASE IN HYDROGEN IONS CONC.
STIMULATE GLUTAMATE DEHYDROGENASE ACTIVITY
GABA ACCUMULATION

23. SUMMARY
 The crrent aerobic atmosphere leads to the formation of
ROS, in plant tissues.
 ROS induce oxidative damages under environmental stress
conditions
.
 Proline act as antioxidant by scavenging ROS and also
function as molecular chaperone to protect protein integrity
and enhance the activities of different enzymes.
 GABA maintains the redox homeostasis by maintaining the
ratios of NADH to NAD+ and NADPH to NADP+ during stress.

24. REFERENCES
 Kilani Ben Rejeb et al. How reactive oxygen species and proline face
stress together, Plant Physiology and Biochemistry,2014,80: 278-284
 Laszlo Szabados et al. Proline: a multifunctional amino acid, Trends
in Plant Science, 2009, 15: 89-97
 Shamsul Hayat et al. Role of proline under changing environments,
Plant Signaling and Behavior, 2012, 7: 1456-1466
 Simon Michaeli et al. Closing the loop on the GABA shunt in plants:
are GABA metabolism and signaling entwined?, Frontiers in Plant
Science, 2015, 6: 419
 Barry J. Shelp et al. Compartmentation of GABA metabolism raises
intriguing questions, Trends in Plant Science, 2012, 17: 57-59
 Kaushik Das et al. Reactive oxygen species (ROS) and response of
antioxidants as ROS-scavengers during environmental stress in plants,
Frontiers in Environmental Science, 2014, 2: 53

25. ACKNOWLEDGMENT
I WOULD LIKE TO EXPRESS MY SINCERE GRATITUDE TO Prof .
A.S.RAGHAVENDRA , Dr. IRFAN A.GHAZI AND Prof. C.H.VENKETRAMANA
FOR THEIR GUIDANCE AND SUPPORT TO WORK ON THE PRESENTATION
Prof. A.S.
RAGHAVENDRA
Dr. IRFAN A. GHAZI
Prof. C.H.VENKETRAMANA
H.O.D
DEPARTMENT OF PLANT
SCIENCES