Different types of abiotic stresses in crops

1. Abiotic Stresses in crops

2. Plants are sessile and must deal with stresses in
place
• Plants cannot avoid stress after germination
• How plants deal with stress has implications in
– Ecology: Stress responses help explain geographic
distribution of species
– Crop science: Stress affects productivity
– Physiology and biochemistry: Stress affects the metabolism
of plants and results in changes in gene expression
Heat-stressed wheat
www.grainscanada.gc.ca
• Stresses cause strains (responses of stressed objects) = changes in
gene expression and metabolism in plants
• Biological stress difficult to define/quantify:
– What is “normal” metabolism?
– Limitations to yield?

3. Stresses are abiotic or biotic
• Stresses cause responses in metabolism
and development
• Injuries occur in susceptible plants, can
lead to impeding flowering, death
• Ephemeral plants avoid stress
– Mexican poppies in US desert SW
– Only bloom after wet winter
– Die before summer returns
Preferable!
ABIOTIC STRESSES
Environmental, non-
biological
• Temperature (high /
low)
• Water (high / low)
• Salt
• Radiation
• Chemical
BIOTIC STRESSES
Caused by living
organisms
• Fungi
• Bacteria
• Insects
• Herbivores
• Other
plants/competition
http://www.geo.arizona.edu/gallery/US/tuc_2.html
Fig. 21.1

4. Plants must be stress resistant to survive
• Avoidance also possible by morphological adaptations
– Deep tap roots in alfalfa allow growth in arid conditions
– Desert CAM plants store H2O in fleshy photosynthetic stems
• Stress resistant plants can tolerate a particular stress
• Resurrection plants (ferns) can tolerate dessication of protoplasm to <7%
H2O  can rehydrate dried leaves
• Plants may become stress tolerant through
Alfalfa plant
– Adaptation: heritable modifications to increase fitness
• CAM plants’ morphological and physiological adaptations to low H2O
environment
– Acclimation: nonheritable physiological and biochemical gene
expression
• Cold hardening induced by gradual exposure to chilling temps, a/k/a cold-
hardy plants

5. Biotic /
Abiotic
constraints
-Drought
-Salinity
-Flooding
-Temperature stresses

6. Drought
• In rice, effect of drought will be severe when it occurs during
reproductive stage.
• Drought affects yield components like panicles/m2, spikelets
per panicle, spikelet fertility and 1000 grain weight.
• inhibition of the elongation of the peduncle
(uppermost internode) resulting in poor panicle
exertion (O'Toole & Namuco, 1983)
• inhibition of anthesis and spikelet desiccation (O'Toole
et al., 1984)
• pollination abnormality (Ekanayake et al., 1990).

8. -Drought escape
-Drought Avoidance
-Drought Tolerance
-Drought Recovery

10. Flooding
• ≈9% of global rice area is flood-prone
• Tamil Nadu – Cauvery delta - 3 lakh ha paddy is affected frequently

12. • ABIOTIC STRESS: Temperature
• Plants exhibit a wide range of Topt (optimum
temperature) for growth
• We know this is because their enzymes have
evolved for optimum activity at a particular T
• Properly acclimated plants can survive
overwintering at extremely low Ts
• Environmental conditions frequently oscillate
outside ideal T range
• Deserts and high altitudes: hot days, cold nights
• Three types of temperature stress affect plant
growth
– Chilling, freezing, heat
Growth temperature
Growth
rate
Topt
Temperature

13. Suboptimal growth Ts result in suboptimal plant development
Chilling injury
• Common in plants native to warm habitats
– Peas, beans, maize, Solanaceae
• Affects
– seedling growth and reproduction
– multiple metabolic pathways and physiological
processes
• Cytoplasmic streaming
• Reduced respiration, photosynthesis, protein
synthesis
• Patterns of protein expression
• Initial metabolic change precipitating metabolic shifts thought to be
alteration of physical state of cellular membranes
• Temperature changes lipid and thus membrane properties
• Chilling sensitive plants have more saturated FAs in membranes: these
congeal at low temperature (like butter!)
• Liquid crystalline  gel transition occurs abruptly at transition
temperature

14. High Temperature Stress?
• Heat stress is defined as the rise in temperature beyond a
threshold level for a period of time sufficient to cause irreversible
damage to plant growth and development.
• usually 10–15 ◦C above ambient, is considered heat shock or heat
stress.
• serious threat to crop production worldwide (Hall, 2001).
• Gaseous emissions due to human activities are substantially
adding to the existing concentrations of greenhouse gases,
particularly CO2, methane, chlorofluorocarbons and nitrous
oxides.
• Different global circulation models predict that greenhouse gases
will gradually increase world’s average ambient temperature.

15. Effect of High Temperature in rice
• Flowering (anthesis and fertilization), and to a lesser
extent booting (microsporogenesis), are the most
susceptible stages of development to temperature in
rice (Satake and Yoshida, 1978; Farrell et al., 2006).
• Among physiological processes occurring at anthesis,
anther dehiscence is perceived to be the most critical
stage affected by high temperature (Matsui et al.,
1997, 2001).

16. At the time of
spikelet opening
2 hrs after anthesis
Anthesis behaviour under normal conditions
Basal
pore
Basal
pore
Apical
pore

17. At the time of spikelet
opening
1 hr after anthesis 3 hr after anthesis
Abnormal anther
dehiscence
Poor pollen
dispersal
Anthesis behaviour during heat stress

18. • There is genotypic variation in spikelet sterility at high
temperature (Matsui et al., 2001; Prasad et al., 2006; Jagadish
et al., 2009))
• It has been suggested that indica spp are more tolerant to
higher temperatures than japonica spp (Matsui et al., 2000),
although heat tolerant genotypes have been found in both
subspecies
• Genotypes Nagina 22 (Yoshida et al., 1981; Prasad et al., 2006;
Jagadish et al., 2009) and Akitakomachi (Matsui et al., 2001)
are the most tolerant genotypes found to date among indica
and japonica spp, respectively

19. Genetic variation for anther dehiscence and pollen tube growth during high
temperature stress in three different rice genotypes viz., Moroberekkan, IR 64
and Nagina 22.

20. wavelength (nm)
10-9 meter
0.000000001 meter!
400 500 600 700 nm
wavelength
violet blue green yellow orange red

21. White Light
Leaf Pigments Absorb
Most Colors
Green is reflected!

22. How Light and Temperature affect
Plants
• Light intensity- growth is greatly reduced at
lower light intensities. Most plants cannot grow
below 100-200 foot candles, about the level of
light in an average room
• The compensation point is the light intensity at
which a plant will maintain itself but not grow
• Temperatures at night are lower, therefore the
plant goes through respiration

23. What wavelengths of light drive photosynthesis?
wavelength (nm)
400 500 600 700 nm
visible spectrum
green light
reflected
Action Spectrum
some still drives
photosynthesis
Photosynthetic
Rate
0
100%
Light beyond 700 nm has
insufficient energy to
drive photosynthesis

24. What intensities of light drive photosynthesis?
Light Intensity (fc)
0 10 100 1,000 10,000 fc
add to reserve
grow
reproduce
Using reserves
and may die
Reaction
Rate
0
100%
Photosynthesis
Respiration
compensation
point

25. Low Light Stress
• Growth and yield
• dried grain production
• Photosynthesis
• Photorespiration

26. High Light
• Both chlorophyll and DNA are easily damaged
by high intensities of direct sunlight
• High light intensities are often coupled with
desiccating conditions.

27. Nutrient Stress
• The 13 mineral nutrients (macronutrients and micronutrients),
which come from the soil, are dissolved in water and absorbed through
a plant's roots. There are not always enough of these nutrients in the
soil for a plant to grow healthy. This is why many farmers and
gardeners use fertilizers to add the nutrients to the soil.

28. • Macronutrients are nutrients required in large quantities.
• Macronutrients can be broken down into two more groups:
• primary and secondary nutrients.
• The primary nutrients are nitrogen (N), phosphorus (P), and
potassium (K). These major nutrients usually are lacking from the
soil first because plants use large amounts for their growth and
survival.
• The secondary nutrients are calcium (Ca), magnesium (Mg),
sulfur (S), iron (Fe). There is usually enough of these nutrients in
the soil, so fertilization is not always needed.
MACRONUTRIENTS

29. • Micronutrients are those elements essential for plant growth which are
required in small (micro) quantities. These elements are sometimes
called minor elements or trace elements.
• The micronutrients are boron (B), copper (Cu), chloride (Cl),
manganese (Mn), molybdenum (Mo), and zinc (Zn).
MICRONUTRIENTS