Waterlogging and submerged

1. Waterlogging and
Submergence Stresses in Plants

11. CO2

17. Excess Water is detrimental for
plants
• Soil waterlogging and submergence/Flooding are
abiotic stresses that influence species composition
and productivity in numerous plant communities,
worldwide.
• Plants require water for growth but excess water
that occurs during submergence or waterlogging is
harmful or even lethal.

18. ‘When water table rises to such an extent that soil surface becomes saturated
with water for at least three months proving detrimental to most of field
crops’’
Water logging may be natural or induced by humans due to high or
perched water table.
• Perched water table:
• Water table of saturated layer of soil which is separated from an
underlying saturated layer by an unsaturated layer
WATER LOGGING

21. • Excess water in the root environment of land plants can
be injurious or even lethal because it blocks the transfer
of oxygen and other gases between the soil and the
atmosphere.
• Crop plants require a free exchange of atmospheric
gases for photosynthesis and respiration.
• Like animals, plants can be easily suffocated if this gas
exchange is impeded.
• The most common impediment to gas diffusion is water
that saturates the root environment in poorly drained
soils or that accumulates above soil capacity as a result
of the overflow of rivers, excessive rainfall or excessive
irrigation.

22. Effects of oxygen deficiency
I) Lack of ATP production ATP low to derive root
metabolism
• Normal ratio of AEC (adenylate energy charge) is 0.8
to 0.9.
• Under extreme flooding conditions AEC ratio may
reach upto 0.15 with in 30 minutes.
AEC = [(ATP) +0.5(ADP)]
[(ATP) +(ADP) + (AMP)]
it tells us how much ATP is present if AEC=1
means all nucleotides have been converted to ATP
and no ADP and AMP available so plant can not
produce ATP

24. III) Reduction in ion uptake
Due to accumulation of toxins and reduction in ion
uptake
IV) Epinasty
common indicator of hypoxic condition is downward
curvature of leaves
Production of ACC and ethylene causing uneven
growth of plant leaves(more growth on upper side
V) Reduction in protein synthesis
due to slow metabolism

26. II) Lack of respiratory substrates, intermediates
• Glucose PA Acetaldehyde Ethanol
• Most of the TCA (Tricarboxylic acid cycle or Krebs or Citric
acid cycle) cycle compounds are not available during hypoxic
condition
• PA rather than to undergo aerobic condition & move into
mitochondria, it remains in cytoplasm producing
toxins(Acetaldehyde , Ethanol) which can cause injury to
roots

27. • Plants are exposed to a reduction in oxygen supply because of the slow
diffusion rate of oxygen in water and its limited solubility.
• Growth is greatly inhibited in the deficiency (hypoxia) or complete
absence (anoxia) of oxygen
• In water-saturated soils roots grow only in a small region near the surface
and do not exploit a large soil volume as they would under aerated
conditions.
• Plants invariably wilt within a few hours to 2-4 d of imposing flooding
stress. Wilting is caused by the inhibition of respiration and loss of ATP
synthesis in the roots. This blocks the ion transport systems that normally
create the gradient in water potential across the root endodermis.
• The impeded gas exchange during soil waterlogging leads to root hypoxia or
anoxia, high CO2 in the root zone, and phytotoxins in reduced soils, all with
consequences for root metabolism, nutrient acquisition, and growth of roots and
shoots.

31. 1. Deficiency / Deprivation of O2
Oxygen has three stages in plants which are given below:
Normaxia
Normal Condition of
Oxygen.
(20.9% at 20 o
C)
-Aerobic Respiration
-Characterized by
aerobic metabolism,
and ATP production
via mitochondrial
oxidative
phosphorylation (30–
36 mol ATP per mol
hexose consumed);
cellular ATP content is
Normal.
Hypoxia
Less supply of Oxygen
(< 20.9 % at 20 o
C)
Characterized by increased
anaerobic metabolism, increased
ATP production via glycolysis
owing to limited availability of O2
for oxidative phosphorylation.
Cellular ATP content is reduced
.
Anoxia
Absence of Oxygen
-Characterized by anaerobic
metabolism, ATP production only
by means of glycolysis (2–4 mol
ATP per mole hexose). Cellular
ATP content is low, and ADP
content is high.
-Reduced root growth (Root
Decay)
-Reduced Energy Supply (ATP
Production)
-Reduced Photosynthesis and
stomatal conductance.

32. Hypoxia and anoxia
The reduction of oxygen below optimal levels, termed
hypoxia, is the most common form of stress in wet soils
and occurs during short-term flooding when the roots are
submerged under water but the shoot remains in the
atmosphere.
Hypoxia will also occur in roots near the surface of
longer-term flood water. The complete lack of oxygen,
termed anoxia, occurs in soils that experience long-term
flooding, in plants completely submerged by water, in
deep roots below flood waters.
Long-term flooding shifts the microbial flora in the soil in
favour of anaerobic micro-organisms that use alternative
electron acceptors to oxygen. As a consequence the soil
tends to accumulate more reduced and phytotoxic forms
of mineral ions such as nitrite (from nitrate) and ferrous
(from ferric) ions and few plants are adapted to growth in
these soils.

35. Effects of O2 deficiency
 Reduced stomatal conductance
 Reduced chlorophyll synthesis
 Increased membrane permeability
 Reduced photosynthesis
 Reduced Respiration
 Reduction in Leaf gas attributes
 Destruction of Photosystem II
 Reduced hydraulic conductivity
 Root injuries
 ROS Production
 Reduced ATP production

36. Mechanisms of Stomatal Closure under Low or Reduced Oxygen Level
1. Reduced Oxygen Supply  Limit/ Reduce root oxygenation  Restrict Root Growth 
Reduced Water uptake  Stomatal Closure.
2. Water Logged Condition Oxidative Damage  Rupture Tonoplast  Cytoplasmic
Acidification (Low pH)  Reduced H-ATPase pump activity  decrease conc. of Na+ ,
K+,  Loss of Cell turgidity  Stomatal Closure
3. Reduced Oxygen Supply  Reduced Level of Aquaporins  Reduced hydraulic
conductivity  Stomata Closure
4. Reduced Oxygen Supply  Increase in ACC (1-amino ethyl cyclopropane) Synthase and
ACC oxidase activity  Increased level of ethylene production  Increase
concentration of ABA  Stomatal Closure

37. • Plants exposed to flooding stress exhibit increased
stomata resistance as well as, limited water uptake
leading to internal water deficit.
• In addition, low levels of O2 may decrease hydraulic
conductivity due to hampered root permeability.
• Oxygen deficiency generally leads to the substantial
decline in net photosynthetic rate.
• However, other factors such as reduced chlorophyll
contents, leaf senescence and reduced leaf area are
also held responsible for decreased rates of
photosynthesis.

40.  Soil pH also affects the turnover of soil organic matter and processes such as
mineralization, nitrification and urea hydrolysis.
 Water logging reduces the endogenous levels of nutrient in different parts of plants.
 However, changes in Eh are influenced by presence of organic matter as well as Fe &
Mn.
 Soil reduction induces the release of cations & phosphorus through adsorption of Ferrous
Ion and dissolution of oxides.
 Soil reducing conditions also favor the production of lactic acid, acetaldehyde and acetic
acid and formic acid.
 The soil pH tends to increase towards neutrality upon water logging.

41. • As soon as O2 is depleted, NO3- is used by some soil microorganisms as an alternative
electron acceptor in their respiration; NO3- is reduced to NH4+, so it becomes the main
form of mineral nitrogen in waterlogged soils.
• In the rhizosphere of roots with radial O2 loss (ROL), however, NH4+ can be converted
back to NO3-, with both these forms of mineral nitrogen absorbed by roots.
• Manganese oxides are the next electron acceptors used by anaerobic microorganisms,
followed by iron oxides resulting, respectively, in elevated concentrations of Mn2+ and
Fe2+ in the soil solution; these soluble forms often increase to levels that are toxic to
plants.

42. • Decrease in the redox potential results in the reduction of SO4
2- to H2S, which is also potentially
toxic. In addition to these inorganic phytotoxins (Fe2+, Mn2+, or H2S), some nutrients change in
availability in flooded soils; e.g., P becomes more available, whereas Zn becomes less available.
• High concentrations of both Mn2+ and Fe2+ are considered to be major constraints for growing
sensitive cultivars of wheat in waterlogging-prone areas of Australia (Khabaz-Saberi et al. 2010);
these elemental toxicities also limit rice yields in many flooded areas around the globe. Also
detrimental to plants is the accumulation of metabolites (e.g. acetic acid, butyric acid, propionic
acid) produced as a result of anaerobic metabolism by microorganisms in waterlogged soils. The
types and amounts of these organic compounds depends upon the fermentative character of the
microorganisms, the organic matter in the soil, and on soil conditions such as pH and temperature.
These compounds can have adverse effects on root growth (e.g. cell division and viability) and
nutrient acquisition (e.g. activity of various membrane transporters, membrane permeability) and,
ultimately, shoot growth (Shabala 2011).

44. Nutrient Imbalance
 Water logging reduces the endogenous levels of nutrient in different parts of plants.
 Oxygen deficiency in the root zone causes a marked decline in the selectivity of K+
/Na+
uptake and impedes the transport of K+
to the shoots.
 It has also been reported in the literature that hypoxic conditions cause decrease in the
permeability of root membranes to Na+
.
 Generally, water logging causes acute deficiencies of essential nutrients such as nitrogen,
phosphorous, potassium, magnesium and calcium.

48. Adaptations against water logging
1) Metabolic adaptations
a)
Plants continue to respire anaerobically and two ATPs are
available
b) Crawford ,s metabolic adaptation
in sensitive plant ethanol and acetaldehyde production and
in tolerant plant reutilization of ATP produced

49. II) Structural Adaptation
a) Root lignification against radial O2 loss
under submerged conditions O2 conc.low in soil than plant
therefore it can go out and additional loss of O2 can occur
Wax type material deposited on roots creating a barrier to
O2 loss.

50. b) Production of aerenchyma cells
• When roots are exposed to anaerobic conditions production
of ACC
• Roots(O2absent) ACC ACCoxidase aerial parts
(abundent O2) Ethylene cellulase& pectinase
aerenchyma (ground tissue with large air spaces) hollow
pipes can transfer oxygen from shoot to shoot
ACC =1-aminoacyl propane-1-carboxylic acid
In rice aerenchyma are produced
within two days

52. Production of aerenchyma in cortical region

56. • Injures of flood to plant
• Flood is actual deficiency in O2
• Anything increases in soluble O2, the injury will
decrease. And anything decreases in soluble O2,
the injury will increase.
• Such as slowly streaming water less damage than
static water.

57. • (1) Injury in morphology and anatomy by O2
deficiency：growth↓，leaf yellowish (nutrition
deficiency），root darkness（low Eh），epinasty
（Eth), air root(IAA, Eth), stem hollow (tissue
degradation caused by Eth ）.
• (2) Injury in metabolism by O2 deficiency:
photosynthesis ↓——stomatal block, inhibition of
CO2 entrance . Anaerobic respiration↑，toxicants:
alcohol ，acetaldehyde，NH3，lactate , H2S。

58. • (3) Nutrition disorder：
• absorption ↓ ，soil N、P、K、Ca loss but H2S、
Fe、Mn ↑，microelements poison.
• (4) Changes in plant hormones：IAA and CTK ↓.
ACC synthesis in root and release of Eth in shoot.
• (5) Mechanical damage and infection by harmful
organism

59. • Mechanism of resistance to flood
• Resistance is different in plants: hydrophytes>land
plants，rice>rape>barley; O. sativa>O. japonica ，
and in growth stages : seedling >other stages,
• (1) Tolerance in tissues：Well-developed aerenchyma 。
• (2) Tolerance in metabolism：mitochondria well
develops in anaerobic conditions, succinic acid
dehydrogenase↑，tolerance to ethanol ; PPP instead of EMP，
NR↑，Glutamate dehydrogenase ↑。

62. Importance of limiting radial O2 loss in
aerenchyma roots
1. Less radial efflux of O2 means longitudinal transport
of O2 is more effective in meeting metabolic
demands of root
2. Radially transported O2 can promote soil microflora
(some good, some bad)
3. Radially transported O2 can keep conc. of toxic ions
and organics lower