BIOCHEMICAL RESPONSES DURING STRESS CONDITION

1. BIOCHEMICAL RESPONSES
DURING STRESS CONDITION
M. KUMARESAN
2016803104
Ph. D. IN FLORICULTURE& LANDSCAPING

2. During their life span, plants can be subjected to a number of
abiotic stresses, like drought, temperature (both high and low),
radiation, salinity, soil pH, heavy metals, lack of essential nutrients,
air pollutants, etc.
When affected by one, or a combination of stresses, a response
is induced by changes in the plant metabolism, growth and general
development
(Van et al., 2011)

3. Plant responses to abiotic stresses are very complex phenomena with
individual characteristics for various species. Abiotic stress reduced more than
50 % of crop yield
According to the United Nations - FAO, up to 26 % of arable land is
subjected to drought and over 20 % of the irrigated land is salt-affected
Rehman et al., 2005
Abiotic stress is known to activate a multigene response resulting in the
changes in various proteins and primary and secondary metabolite
accumulation
Paweł et al ., 2014

4. Photosynthesis and carbon metabolism – under stress
Abiotic stresses disturb cell homeostasis and affect
photosynthetic metabolism. The main reason is stomata closure, which
leads to decrease in internal CO2 concentration
(Cornic, 2000)
Drought, salinity, high/low temperatures, ultraviolet radiation and
excessive light generate additional oxidative stress caused by enhanced
production of reactive oxygen species, which further damages the
photosynthetic machinery
(Mittler, 2002)

5. ROS - formed during normal aerobic metabolic processes (like PS and RPN)
and majority of ROS are produced in the mitochondria, chloroplast,
peroxisomes, plasma membrane and apoplast
(Ahmad et al., 2008).
Other sources of ROS production are NADPH oxidases, amine
oxidases and cell-wall peroxidases
(Mittler, 2002)
Oxidative stress - physiological changes - formation of excess
quantities of ROS
(Vangronsveld & Clijsters, 2010).

6. Effect on ROS production
stress
Water potential decreased
Synthesis of ABA in
mesophyll cells
ABA move to guard cells
K+ & water move out of
guard cells
Stomata closing
Limited CO2 supply
Reduced Carbon Reduction
Unavailability of
NADP
Free Electrons
ROS production

7. REACTIVE OXYGEN SPECIES PRODUCTION
O2 + e- O2
-
O2
- + O2 H2O2
H2O2 + O-
2
OH* + OH-
Super oxide
Hydrogen Peroxide
Hydroxyl radical

8. ROS removal enzymes are superoxide dismutase (SOD), which is
one of the most effective antioxidants, which catalyzes the removal of O 2
- by its
dismutation to H 2O 2 and O 2
The regulation of the ROS-scavenging enzymes differs between the
plant species, depending on the tolerance level to the stress and its intensity
The increased activities of APX and SOD were found in varieties of
beans in response to drought
(Mittler 2002).

9. ROS effect in different cellular components
ROS - affect lipids, proteins, carbohydrates and DNA
Moller et al. (2007)
Proteins - suffer oxidation by ROS, causing certain enzymes to
lose its catalytic function
DNA - attacked by ROS damaging nucleotide bases, causing
mutations and genetic defects
(Tuteja et al., 2001)

10. Plants under stress conditions molecular oxygen (O2) acts as an electron
acceptor, giving rise to the accumulation of ROS
Singlet oxygen (1O2), hydroxyl radical (OH−), superoxide radical (O− 2),
and hydrogen peroxide (H2O2) are all strongly oxidizing compounds and therefore
potentially harmful for cell integrity
Durner et al., 2013

12. This short review briefly introduces the formation of reactive oxygen species
(ROS) as by-products of oxidation/reduction (redox) reactions, and the ways in
which the antioxidant defense machinery is involved directly or indirectly in ROS
scavenging. Major antioxidants, both enzymatic and non enzymatic, that protect
higher plant cells from oxidative stress damage are described. Biochemical and
molecular features of the antioxidant enzymes superoxide dismutase (SOD),
catalase (CAT), and ascorbate peroxidase (APX) are discussed because they
play crucial roles in scavenging ROS in the different cell compartments and in
response to stress conditions. Among the non enzymatic defenses, particular
attention is paid to ascorbic acid, glutathione, flavonoids, carotenoids, and
tocopherols. The operation of ROS scavenging systems during the seasonal
cycle and specific developmental events, such as fruit ripening and senescence,
are discussed in relation to the intense ROS formation during these processes
that impact fruit quality. Particular attention is paid to Prunus and Citrus species
because of the nutritional and antioxidant properties contained in these
commonly consumed fruits.

13. Biochemical features of the antioxidant enzymes superoxide
dismutase (SOD), catalase (CAT), and ascorbate peroxidase (APX)
they play crucial roles in scavenging ROS in the different cell
compartments and in response to stress conditions
Among the non enzymatic defenses- ascorbic acid, glutathione,
flavonoids, carotenoids, and tocopherols more important for
scavenging ROS

14. Stress tolerance is positively correlated with the activity of antioxidant
enzymes, such as superoxide dismutase (SOD), catalase (CAT),
glutathione peroxidise (GPX), ascorbate peroxidase (APX), and
glutathione reductase (GR)
Tuteja et al., 2013

15. Role of primary metabolites in response to abiotic stress
Amino acids
Increased content of some amino acids, including proline,
tryptophan, phenylalanine and histidine in maize and Potato subjected to
drought stress
(Witt et al. 2012), (Robinet et al. 2008).

16. Polyamines
Polyamines may act as a cellular signal during stress. Its levels
changing under environmental stress conditions
Gill and Tuteja, 2010
Carbohydrates
Abiotic stresses that lead to accumulation of nonstructural
carbohydrates like sucrose, hexoses and polyhydric alcohols among many
plant species
(Bartels and Sunkar, 2005)

17. Glycine betaine
Quaternary ammonium compound, which is involved in maintaining
water balance, stabilizing macromolecules, protecting photosynthesis
and detoxificating reactive oxygen radicals
(Chen and Murata 2011)
Tomato plants were more tolerant to chilling stress due to increase
in glycine betaine
(Park et al. 2004)

18. Role of secondary metabolites in response to abiotic stresses
Secondary metabolites play an important role in many biochemical and
biophysical processes occurring in plant cells and tissues
Ahuja et al., 2010
Phenolic compounds
Accumulation of phenolic compounds is regulated by environmental
stresses, such as UV irradiation, light, Nutrient deficiencies
Ramakrishna and Ravishankar, 2011

19. Cold stress induces the production of phenolic compounds and
Lignins constitute an important stress defense mechanism
Lignification and suberin deposition may play a significant role in the
improved resistance to cold stress (Janska et al. 2010)
Biosynthesis of flavonoids, isoflavonoids and anthocyanins is
stimulated by various environmental stresses
Flavonoids have protective functions in plants exposed to water
deficit because of their antioxidant properties
(Herna et al. 2006)

20. Water stress, both water logging and drought, increased the level of
flavonoids, quercetin and rutin in Hypericum brasiliense
(Abreu and Mazzafera 2005)
Forty seven flavonoids were identified in leaves of two citrus species
and most of their contents changed in response to flooding

21. Terpenoids
Terpenoids show an antioxidant and antibiotic activity and it
improve environmental stress tolerance
(Cheng et al. 2007).
Brassica juncea, the increased content of tocopherol plays an
important role in the alleviation of stress induced by salt, heavy metal and
osmotic potential
(Yusuf et al. 2010)
Saponins were identified as one of the key secondary metabolites
correlated with salt tolerance in soybean
(Wu et al. 2008).

22. Nitrogen-containing secondary metabolites
Glucosinolates are plant secondary metabolites that contain sulfur and
nitrogen and are derived from glucose and amino acids
Drought stress and water-logging led to increased aliphatic glucosinolate
and flavonoid levels
(Mewis et al. 2012).
Increased glucosinolate content was observed in Brassica napus leaf
tissue - water deficit - during vegetative growth
(Jensen et al. 1996).

23. Another group of nitrogen-containing secondary metabolites are
alkaloids. Most of these compounds have bitter taste and play an important role
during the plant defense in abiotic stress
Poppy (Papaver somniferum) produced a higher level of the alkaloids
under drought conditions
(Szabo et al. 2003)

24. Stress effects on amino acids
Mansour (2000) many amino acids including proline, alanine,
arginine, glycine, serine, leucine, and valine and the non-protein amino
acids (citrulline and ornithine) and amides (glutamine and asparagines)
accumulate in plants exposed to salt stress

25. Salt stress - accumulate a number of metabolites, termed compatible
solutes, because they do not interfere with the plant metabolism
(Sivakumar et al., 2000)
Among these solutes, proline is widely distributed in plants and it
accumulates in larger amounts than other amino acids in salt-stressed plants
(Ashraf and Foolad, 2007)
Proline accumulation is one of the most frequently reported
modifications induced by water deficit and salt stress in plants, and it is often
considered to be involved in stress tolerance mechanisms
(Manivannan et al., 2007)

26. Proline acts as a cytosolic osmoticum, scavenger of OH∙- radical
and can interact with cellular macromolecules, such as DNA, protein,
membranes, and can stabilize their structure and function
(Kavi et al., 2005)

27. Soluble proteins
Salt stress proteins, which accumulate only due to salt stress,
and stress associated proteins, which also accumulate in response to
heat, cold, drought, water logging, and high and low mineral nutrients.
Proteins that accumulate in plants grown under saline conditions
may provide a storage form of nitrogen that is re-utilized when stress is
over and may play a role in osmotic adjustment

28. Heat shock proteins
HSP are the group of stress proteins broadly expressed upon temperature
stress (5-10oC above the normal growing temperature of the organism)
The HSP homologous which are expressed in cells during normal cell
growth and differentiation are called Heat Shock Cognates (HSC)
(Vishwanathan and Chopra, 1996).

29. Role of HSPs
 HSPs prevent accumulation of degraded protein resulted in response to
exposure to high temperature
 HSPs protect the protein and degrade the denatured proteins
 In soybean, both high and low molecular weight HSPs protected soluble
proteins from heat denaturation

30. Stress effects on carbohydrates
Parida et al. (2002) found that salinity reduced starch and increased
reducing and non-reducing sugars in leaves of Bruguiera parviflora
Khavari-Nejad and Mostofi (1998) indicated that the contents of
soluble sugars and total saccharides are increased significantly, but the starch
content was not affected in leaves of tomato under salinity

31. Increase- proline and soluble sugar in Artemisia herba-alba - under water
deficit stress Guenaoui et al., 2008
Stressed plants accumulated highly soluble sugar content in
solanum tuberosum
Mohsenzadeh et al., 2006
Proline accumulation was considered as an indicator of plant tolerance to
drought conditions
Scheirs et al ., 2005

32. Proline acts as a cytosolic osmoticum, scavenger of OH∙- radical and can
interact with cellular macromolecules, such as DNA, protein, membranes, and can
stabilize their structure and function
(Kavi Kishor et al., 2005)
Glycinebetaine and proline play an adaptive role in mediating osmotic
adjustment and protecting the sub cellular structures in stressed plants
Hsu et al., 2003

33. In Lettuce, accumulation of UV-B absorbing compounds (flavonoids,
carotenoids and phenols) in response to DS is likely to offer some increased
protection from UV-B
Jalal et al ., 2014
Mittova et al., 2002, found that higher salt tolerance of wild tomato
(Lycopersicon pennellii) as compared to cultivated tomato (L. esculentum)
was correlated with increased activities of SOD (superoxide dismutase), APX
(ascorbate peroxidase), and POD (guiacol peroxidase)

34. Thank you