The document discusses abiotic stress responses in plants, with a focus on drought stress. It defines abiotic stress and describes different types of drought stress and plant responses. It discusses the genetic basis of drought tolerance and key pathways involved. The document summarizes stress tolerance mechanisms in plants, including detoxification, chaperoning, late embryogenesis abundant proteins, osmoprotection, and water and ion movement. Case studies on transgenic crops with improved drought tolerance are also mentioned.

1. Abiotic stress responses in
Plants with special reference
to drought
Presented by
Shobha Devidas Surbhaiyya
M.Sc. Agril. Biotech, Dr. PDKV, Akola

2. Introduction
Abiotic stress and its mechanism
Drought stress and its types and synthesis of compatible solutes
The genetic bases of drought tolerance
The abscisic acid transcriptional regulation pathway
Plant response to abiotic stress
Plant responses to abiotic stress
Stress tolerance mechanism
Detoxification
Chaperoning
Late embryogenesis abundant protein function
Osmoprotection
Water and ion movement
Case study

3.  Abiotic stresses are serious threats to agriculture and the environment
 Abiotic stress leads to a series of morphological, physiological,
biochemical and molecular changes in plants that adversely affect growth
and productivity.
 Abiotic stresses cause losses worth hundreds of million dollars each year
due to reduction in crop productivity and crop failure.

4. What is stress:-
External conditions that adversely affect growth, development
or productivity.
Types of stresses:-
 Biotic:- Imposed by organism(i.e. living things)
 Abiotic:- Arising from an excess or deficit in the physical
The term abiotic stress refers to factors such as sub and supra
optimal temperature, excess salt level, reduced water availability leading
to dehydration stress, excess water resulting in flooding stress and
oxidative stress.

5. 1. Avoidance - Drought avoidance is performed by maintenance of turgor
through roots grow deeper in the soil, stomatal control of transpiration and
by reduction of water loss through tissues.
2 Tolerance – It is the ability to withstand water-deficit with low tissue water
potential. Drought tolerance is the maintenance of turgor through osmotic
adjustment (a process which induces solute accumulation in cell), increase in
elasticity in the cell and decrease in cell size.
3 Escape - : It is defined as the ability of a plant to complete its life cycle
before supply of water in soil is depleted and form dormant seeds before the
onset of dry season .

6.  An extended period of deficient rainfall < 75% as compared to normal
rainfall of the region is called drought.
 The limitations of water over a prolonged period of time or In plant denotes
the loss of water from tissues and cells
 Water stress may arise as a result of two conditions, either due to excess of
water or water deficit
 Drought is the most significant environment stress on agricultural
production and enormous effort is being made by plant scientist to
improve crop yields in the face of decreasing water availability.

7. 1. Meteorological Drought- rainfall < 25 % of the average of the
region.( <50 %- severe drought)
2. Agricultural Drought- lack of rainfall result in insufficient moisture
in the root zone.
3. Hydrological Drought- extended dry period leading to marked
depletion of surface water leading to drying up of reservoir, lacks
,streams, rivers etc.

8. 1. Effect on Growth: Reduction in Turgor Pressure, due to cell sizes will be
smaller.
2. Effect on Photosynthesis: Photosynthesis decreases, stomatal closure,
decrease in electron transport.
3. Decrease in nuclear acids and proteins: Protease activity↑, free a.a.↑,
RNAase activity↑，RNA hydrolysis, DNA content falls down.
4. Effect on Nitrogen Metabolism: Nitrate reductase activity↓
5. Effect on Carbohydrate metabolism: Loss of starch and increase in simple
sugars, carbohydrate translocation decreases.

9.  Almost all organisms, ranging from microbes to animals and plants,
synthesize compatible solutes in response to osmotic stress.
 Compatible solutes are nontoxic molecules such as amino acids, glycine
betaine, sugars, or sugar alcohols which can accumulate at high
concentration without interfering with normal metabolism.
 They may have a role in osmotic adjustment, stabilizing proteins and cell
structures, scavenging reactive oxygen species.

10. PROLINE
 Proline is the most widely distributed osmolyte; in plant- it is produced from
ornithine under normal condition but under stress it is made directly from
glutamate.
 Roles: Osmotic adjustment, membranes protection, etc
 Synthesis can occurs via two biosyntetic pathways:
1. The ornithine dependent, and
2. The glutamate dependent (under stress conditions).
Glutamate-Glutamate phosphate-Glutamate semialdehydes- Proline
P5CS – pyrroline-5-carboxylate synthatase
P5CR- pyrroline-5-carboxylate reductase

11.  Glycine betaine is a quaternary ammonium compound that functions as an
osmoprotectant.
 Maintenance of the water balance between the plant cell and the
environment and by stabilizing macromolecules.
 Glycine betaine is synthesized via a two-step oxidation of choline:
Choline→betaine aldehyde→ glycine betaine.
1. The first reaction is catalyzed by a ferredoxin-dependent choline
monooxygenase (CMO)
2. The second step by a NAD+-dependent betaine aldehyde dehydrogenase
(BADH).

12.  Sugars : Sucrose,Trehalose, Fructans
 Polyols : Mannitol, Sorbitol, myo-inositol,
(Sugar alcohols)
 Amino Acids : Proline, Ectoine
 Quarternary amines : Glycine betaine (GlyBet), Proline betaine, Alanine
betaine, 4-hydroxy proline betaine
 Ions : Potassium
 Proteins : LEA/dehydrins, SOD/catalase
 Pigments : Anthocyanins, Betalines,Carotenoids

13. Expression studies have shown that drought specific genes can be grouped
into three major categories
1. Genes involved in signal transduction pathways and transcriptional
control
2. Genes with membrane and protein protection functions
3. Genes assisting with water and ion uptake and transport

16. The outcome of stress signal perception, transduction and
transcriptional up or down regulation of gene is the production of molecules
with various plant protection, repair and stabilization functions.
This molecule can be broadly grouped into five functional groups
1. Detoxification
2. Chaperoning
3. Late embryogenesis abundant protein function
4. Osmoprotection
5. Water and ion movement

17.  To prevent stress injury, cellular ROS needs to remain at nontoxic level
under drought stress
 Antioxidant involve in plant strategies to degrade ROS include,
1. Enzymes such as catalase, superoxide dismutase, ascorbate peroxidase
2. Non-enzyme such as ascorbate, caratenoide, glutatione etc.
 Some proteins, osmolytes have antioxidative functionality

18.  LEA protein are produced in response to dehydration stress.
 They play role in water status stabilization, production of cytosolic
structure , transport of nuclear targeted protein, prevention of
membrane leakage.
 LEA and LEA type genes are found in plant, they accumulate in seeds
during the late stage of embryogenesis.
 E.g. – The barley group 3 LEA gene, HVA1 was constitutively over
expressed in rice plant to increase drought tolerance.

19.  Chaperoning functions involve specific stress associated proteins
 It is responsible for protein synthesis, targeting, maturation and
degradation and also membrane stabilization
 HSPs, which are induced by heat, have been implicated in plant cell
protection mechanisms under drought stress
 One such protein, Nt HSP 70-1, was constitutively overexpressed in
tobacco at as certain it’s role in plant drought response and tolerance(cho
and hong 2006)

20.  Osmoprotection involves the upregulation of compatible solutes
(osmolyte) that function primary to maintain cell turgor, but are also
involved in antioxidation and chaperoning through direct stabilization of
membrane .
 Compatible solute are low molecular weight, high soluble compound that
are usually nontoxic at high cellular concentration.
 The three major groups of compatible solutes are
1. Amino acids (eg. proline).
2. Amines (glycine betaine, polyamines).
3. Sugars(mannitol, trehalose).

21.  Water and ions move through plants via transcelluar and interacellular
pathway.
 Aquaporins (major intrinsic protein, MIPs) which are either tonoplast or
plasma membrane localized, facilitate water, glycerol, small molecules
and gas transfer through membrane and therefore have a role in water
homeostasis.

24.  Kole et.al, Transgenic crops plant, Springer Verlag Berlin Heidelberg 2010.
 Dhariwal et.al, Genetic engineering for abiotic stress tolerance in plant ,
plant biotechnology, 15(1) 1-10.1998.
 Yang et.al, Narrowing down the target, towards successful genetic
engineering of drought tolerant crop, molecular plant, vol-3:469-490,
2010.
 Ajay K. Garg, Trehalose accumulation of rice plant confer high tolerance
level to different abiotic stresses, vol-99: 25, 2002.