Waterlogging is one of the main abiotic stresses suffered by plants. Inhibition of aerobic respiration during waterlogging limits energy metabolism and restricts growth and a wide range of developmental processes, from seed germination to vegetative growth and further reproductive growth.

1. Academic Year:- 2022-2023
Banda University of Agriculture and Technology, Banda (U. P.)
ASSIGNMENT
Title of Assignment: Waterlogging Stress in Plants
Course Code: MBB 517
Course Name : Stress Biology and Genomics
Instructed by- Dr. Shalini Purwar
210001
Submitted by : Name: Ashna Fiza
Student ID.: 2309
Degree Programme :-M.Sc.(Ag.)
Biochemistry

2. Arising from another
organism
• Drought or Waterlogging
• Heat Temperature
•Chilling and Freezing
•UV Radiation
•Salinity
•Heavy Metal
NO LITTERING
STRESS AND
TYPES OF
STRESS
BIOTIC STRESS ABIOTIC STRESS
•Any deviation in optimal condition of any factor
essential for its growth will lead to aberrant change in
physiological processes and due to this plant body will
experience tension and this state referred as plant stress.
•Reduction in growth, yield and death of the plant or
plant part. Stress may be caused due to biotic (disease,
herbivores) or abiotic (Physical and chemical)
factors(Nilsen & Orcutt, 1996).
Arising from an excess or
deficit in the physical or
chemical environment
•Herbivory
•Pathogens and Parasites
•Allelopathy
Ashna Fiza
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3. WATERLOGGING STRESS-
AN INTRODUCTION
Waterlogging is one of the main abiotic stresses suffered by
plants. Inhibition of aerobic respiration during waterlogging
limits energy metabolism and restricts growth and a wide range
of developmental processes, from seed germination to
vegetative growth and further reproductive growth. Plants
respond to waterlogging stress by regulating their
morphological structure, energy metabolism, endogenous
hormone biosynthesis, and signaling processes. In this updated
review, we systematically summarize the changes in
morphological structure, photosynthesis, respiration, reactive
oxygen species damage, plant hormone synthesis, and signaling
cascades after plants were subjected to waterlogging
stress.Water logging refers to a condition when water is present
in excess amount than its optimum requirement. It creates an
anaerobic situation in the rhizosphere due to which the plant
experiences the stress (O2 deficient stress).
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NATURE OF WATER LOGGING
STRESS
In the water logged soils, water gets filled in the pores of the soil
which are previously occupied by O2. Such soils suffer O2
deficiency.This O2 deficiency depresses growth and survival of
plants growing in it. Flood sensitive plants (eg. Tomato, soybean
and sunflower) are killed in the water logged conditions, while the
tolerant species (eg. Rice) withstand water logging for a
considerable time. However, continuous submergence of rice for
more than 10 days is also deleterious resulting in death and decay
of the plants.

4. PLANT WATER RELATIONS IN
FLOODING STRESS
The flooding often induces stomatal closure mostly in C3
plants. This causes lower water flow in these plants. This also
results in leaf dehydration because of reduced root
permeability. Ultimately, wilting of leaves occurs due top the
restricted water flow from the roots to the shoots.
Occurrence of these changes in leaves, shoots or roots is due to
the transfer of toxic substances (acetaldehyde / alcohol)
produced under anaerobic conditions in the roots as well as the
levels of plant growth regulators (PGRs) transported from the
roots to shoots via transpiration stream.
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LEVELS OF ENDOGENOUS
PGRS(PLANT GROWTH
REGULATORS)UNDER
FLOODING STRESS
Endogenous levels of PGRs such as GA( Gibberellic Acid)and
cytokinins (CK) are reduced in the roots. This has enhanced levels
of ABA and ethylene in the shoots causing stomatal closure and
early onset of senescence respectively.It is also reported that levels
of auxins are reduced and that of Aminocyclopropane -1-
Carboxylic Acid (ACC), precursor for the ethylene biosynthesis are
increased under flooding stress.

5. Important roles played by these endogenous PGRs
during high moisture (flooding) stress are
summarized in the following table.
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Level of PGR in plants
Effects on plants under
water logging
Reduced Auxins
Causes “Hypertrophy” (Swelling of
stem base by collapse or
enlargement of cells in cortex)
Decreased GA
Decreased CK
Increased ABA
Increased Ethylene
Causes reduction in cell
enlargement and stem elongation
Results in early on-set of
senescence and reduced rate of
assimilate partitioning to the sinks
Cause stomatal closure with
consequential decrease in the rate of gas
exchanges during photosynthesis,
respiration and transpiration; results in
efflux of K+ from the guard cells;
decreases ion transport due to lower rate
of transpiration; decrease the starch
formation in the guard cells resulting in
stomatal closure
Causes “Epinasty” of leaves (uneven
growth of leaves due to more cell
elongation on upper side than the
lower side of the leaf); induces
senescence and Hypertrophy in plants.
Thus, the O2 stress in the roots under flooding produces
signals, via transpiration stream, to the leaves affecting
stomatal behaviour ultimately.

6. ii. Effects on Photosynthesis:Under flooded condition, plant
roots remain submerged while shoots are generally above the
water level. Although the shoots are not directly influenced by
anaerobic conditions, but they respond to the metabolic
conditions of roots.One of the immediate effects of root zone
flooding is stomatal closure of leaves. As a consequence of
increasing stomatal resistance, photosynthesis decreases quickly
following flooding. Besides stomatal inhibition of
photosynthesis, direct inhibition of photosynthetic enzymes
may also occur by H2S, a product of submerged soil.
DETRIMENTAL EFFECTS OF
FLOODING STRESS ON
METABOLISM:
i. Effects on Respiration:A reduction in aerobic respiration in
roots is the initial effect of anaerobic soil conditions. Since
conservation of energy in the form of ATP is much less in
anaerobic respiration, the amount of ATP, the total energy
profile of root cells and the ATP/ADP ratio are reduced under
flooded condition.
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7. Because of the relative inefficiency of anaerobic respiration as
opposed to aerobic respiration, roots of plants under flooded
condition demand a utilization of a large amount of
carbohydrate. As a result root tissues rapidly become depleted
in carbohydrates and this situation has been very often
described as “carbohydrate starvation” during flooding.
Furthermore, the roots experience an increased carbohydrate
starvation because translocation of carbohydrates from leaves
(source) to roots (sink) is hampered during flooding conditions.
The accumulation of inhibitory plant hormones in leaves may
also cause non-stomatal inhibition of photosynthesis.
Translocation of cytokinins from roots to leaves suffers a
decline during flooded condition, while translocation of ABA
and ethylene increases.
It is envisaged that hypoxia in roots induced by flooding, leads
to an increase in ethylene biosynthesis and its translocation.
This is because the internal tissue like the stele of the roots is
totally devoid of oxygen (anoxic) as compared to the peripheral
cortical tissues with less oxygen (hypoxia).
It is known that the last enzyme in the ethylene biosynthetic
pathway (ACC oxidase) requires O2 and stops in anoxic
condition, while another key enzyme, ACC synthase activity
increases in centre of roots (anoxic), ACC diffuses to outer cells
(more hypoxic), where ACC oxidase can complete ethylene
synthesis.
Ethylene also induces aerenchyma formation and through such
gas passages ethylene transport from root to leaves may
increase.
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8. iii. Effects on Water and Nutrient Relations:
Flooding with salt water creates an osmotic stress. On the other
hand, flooding with fresh water may decrease root permeability
to water and root hydraulic conductance. As a consequence,
wilting symptom may result from flooded condition.
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Flooding induces the formation of adventitious roots which are,
however, more permeable to water and hence are able to
enhance water transport to shoot. Total water flow in plants
will be less because adventitious roots have inferior hydraulic
conductance.
Anaerobic respiration is unable to provide adequate ATP for
active nutrient uptake. Thus, nutrient accumulation in flooded
situation is very much limited. Transpiration is reduced by
flooding and as a result the rate of delivery of nutrients,
dissolved in xylem fluid, to the shoots is reduced. A rapid
occurrence of chlorosis may happen in sensitive plants after
flooding because of reduced nutrient uptake and iron toxicity.

9. ADAPTATIVE RESPONSE TO
WATERLOGGING STRESS
i. Development of Aerenchyma:
Flooding induces the formation of gas spaces called
aerenchyma in different plant parts like roots, rhizome, stem,
petioles and leaves. It is now believed that aerenchyma tissue
helps in proper growth of roots and their survival under
reduced O2 regime.
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ii. Reorientation of Leaves and Stems:
It has been suggested that petiole epinasty in response to
flooding may be an adaptive response enabling plants to
withstand stress. Such epinasty response is caused by ethylene
production in the shoots of plants, which is induced by
flooding. In roots growing under anaerobic condition, ACC,the
immediate precursor of ethylene, cannot be converted to
ethylene.
iii. Adventitious Root Formation and Hypertrophy:
During flooding, the old roots are replaced by adventitious
roots, which act as a survival mechanism. Resistance to
flooding is found to be correlated with adventitious root
formation. Water and nutrient uptake in flood-resistant plants
are facilitated by adventitious roots. Auxin and ethylene may
be involved in the formation of adventitious roots, which is
induced by flooding.The ability of flooding to induce
hypertrophy at the base of the stem has been observed in a
number of plants.

10. ADAPTATIVE RESPONSE TO
WATERLOGGING STRESS
iv. Fast Shoot Elongation Under Water:
Deep water rice plants show a unique physiological adaptation
with an enhancement of inter-nodal length. As a result, the
leaves are kept above water level, which permits the movement
of air to the submerged plant parts. Ethylene has been shown to
be responsible for internode elongation of deep-water rice.
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v. Biochemical Changes Induced by Flooding:
Two theories have been proposed to explain flooding tolerance.
According to Crawford’s metabolic theory for flooding
tolerance reported in 1971, it has been stated that flooding
tolerance depends on reduction in ethanol production.
This can be achieved by low alcohol dehydrogenase (ADH)
activity, which reduces the accumulation of ethanol having
toxic effects. Flooding tolerance has been related with the
ability to shift glycolytic intermediates to alternate end
products like malate, lactate and other organic acids.

11. MITIGATION OF
WATERLOGGING
Providing adequate drainage for draining excessive
stagnating water around the root system.
Spray of growth retardant of 500 ppm cycocel for arresting
apical dominance and thereby promoting growth of laterals
Foliar spray of 2% DAP + 1% KCl (MOP)
Nipping terminal buds for arresting apical dominance and
thus promoting growth sympodial branches (as in cotton)
for increasing productivity
Spray of 40 ppm NAA for controlling excessive pre-mature
fall of flowering/buds/young developing fruits and pods
Spray of 0.5 ppm brassinolide for increasing photosynthetic
activity
Foliar spray of 100 ppm salicylic acid for increasing stem
reserve utilization under high moisture stress
Foliar spray of 0.3 % Boric acid + 0.5 % ZnSO4 + 0.5 %
FeSO4 + 1.0 % urea during critical stages of the stress
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12. IMPORTANT ROLE OF
HORMONES DURING
WATERLOGGING
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Plant hormones play a key role as mediators between
environmental signals and adaptive plant responses. Auxin,
ethylene and gibberellins are involved in the initiation of
adaptive plant responses such as the development of
adventitious roots and stimulated shoot elongation upon
flooded conditions.
Flooding leads to either partial or complete submergence
stress, and it imposes hazards for plant growth and
development from seed germination to grain filling. Leaf petiole
movement, stomatal closure, shoot elongation, and formation
of adventitious roots/lateral roots/aerenchyma are obvious
morphological alterations induced by hypoxia.
Carbon/nitrogen metabolism, photosynthesis, ion homeostasis,
programmed cell death, hormone signaling, as well as other
cellular metabolisms work in synergy in flooded plants.

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ETHYLENE SIGNALING IN
PLANTS DURING
FLOODING/WATERLOGGING
Flooding is detrimental for plants mainly due to restricted gas
exchange underwater, which further induces rapid
accumulation of ethylene in plant cells.Ethylene is considered
the major regulator of plant adaptation to flooding stress, such
as raising plants by aerenchyma, facilitating gas diffusion by
adventitious roots, directing antithetical strategies for plant
survival by shoot elongation, and elevating leaves above water
based on hyponastic growth.Ethylene is also extensively
characterized as an essential phytohormone for recovery after
hypoxia by replenishing tricarboxylic acid cycle substrates ,and
post-submergence induced ethylene could interplay with ROS,
photoinhibition, and desiccation to modulate plant growth
during anoxia reoxygenation.This section, ethylene signaling in
plant responses to flooding stress are summarized below...
Figure-Ethylene signaling involved in plant response to flooding. Flooding increases ethylene amount and
subsequently induces RAP2.3, ERF2, Sub1A, EILa/b, PIP2;1/2;4/2;5 to modulate fermentation, root architecture,
GA homeostasis, and water transport capacity in Arabidopsis, rice, soybean, Actinidia deliciosa, Petunia (Petunia
× hybrida), and Populus tremuloides. ADH, alcohol dehydrogenase; ERF2, ethylene response factor2; EIL,
ethylene insensitive like; GA, gibberellic acid; PCD, programmed cell death; PDC, pyruvate decarboxylase; PIP,
plasma membrane intrinsic protein; RAP2.3, related to apetala 2.3; SD1, SEMI-DWARF1; SK1/SK2,
SNORKEL1/SNORKEL2; Sub1A, Submergence1A; XTH, xyloglucan endotransglycosylases/hydrolases.

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ABSCISIC ACID SIGNALING IN
PLANTS DURING
FLOODING/WATERLOGGING
It is widely accepted that plant responses to flooding stress are
mainly regulated by ethylene signaling, and the interplays of
ethylene and other phytohormones have been documented.
ABA signaling is associated with quiescent or escape strategies
employed by plants based on the differential induction of ABA-
dependent pathways, which can direct stem elongation though
interactions with ethylene and GA.Although the roles of ABA
in flooding responses have been overshadowed by ethylene and
GA, it participates in the emergence of adventitious roots,
formation of secondary aerenchyma, hyponastic growth under
hypoxia, as well as recovery from hypoxia. ABA signaling in
plant response to flood is presented below..
Figure-ABA signaling involved in plant response to flooding stress. Flooding alters ABA content with
different accumulation patterns. The impact of exogenous ABA on flooded plants during seed germination
and seedling establishment are summarized based on reported genes and proteins related to coleoptile
elongation, root growth, cell wall integrity, energy provision, and stomatal opening in Arabidopsis, rice, and
soybean. ABA, abscisic acid; CDC5, cell division cycle 5; Chap20, chaperone 20; ENO, enolase; GRPs, glycine
rich proteins; NAC, nascent polypeptide associated complex; PDC1, pyruvate decarboxylase1; PGIP,
polygalacturonase inhibiting protein; Rrp5, RNA binding rRNA processing protein 5; SAG113, senescence-
associated gene 113; ZFPs, zinc finger proteins.

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OTHER PHYTOHORMONE
SIGNALING IN PLANT DURING
FLOODING/WATERLOGGING
A series of publications has proven that ethylene is the primary
signal for plant adaptation to flooding; additionally, ethylene
modulates a hormone cascade of ABA, GA, and auxin to
induce adventitious rooting, internode elongation, and
carbohydrate degradation.Additionally, the effects of BR, JA,
and salicylic acid (SA) on improving plant tolerance to flood
are either independent or dependent on ethylene signaling to
facilitate plant growth through activation on formation of
adventitious roots, shoot elongation, photosynthetic pigment,
and ROS scavenging.Herein, phytohormone signaling,
including GA, auxin, BR, JA, and SA, is described below...
Figure-Interplays of GA, ABA, auxin, BR, ethylene, and JA signaling involved in plant response to flooding. The
scheme of GA, ABA, auxin, BR, ethylene, and JA signaling associated with coleoptile growth, adventitious rooting,
and stem elongation was constructed based on identified genes in Arabidopsis, rice, and maize. Flooding
suppresses expression of miR393, which inhibits OsTIR and OsAFB, altering auxin mediated coleoptile growth
during seed germination. Although auxin receptors and transports are affected differently by flooding,
activation of PIN1/AUX1/AFB2 and suppression of LAX1/LAX3/PIN4/PIN7 improves adventitious rooting through
auxin signaling. Meanwhile, gain-of-function of RAP2.12 activates AtPIN2 for auxin transport. The interaction
between JA and auxin is evident in the enhancement of JA biosynthesis in plants overexpressing ZmPgb1.2.
Flooding induces expression of Sub1A and rice bearing Sub1A presented high amounts of BR, leading to a
reduction in GA content. Furthermore, flood-induced ethylene activates OsEIL1a that binds to SD1, leading to an
increase in GA, which modulates stem elongation through ACE1 and DEC1. ABA, abscisic acid; ACE1, ACCELERATOR
OF INTERNODE ELONGATION1; AFB, auxin signaling F-box; AUX, auxin resistant; BR, brassinosteroid; DEC1,
DECELERATOR OF INTERNODE ELONGATION1; EIL1a, ethylene insensitive like1a; GA, gibberellic acid; JA, jasmonic
acid; LAX, like AUX; Pgb, phytoglobin; PIN, plasma membrane intrinsic protein; RAP2.12, related to apetala 2.12;
SD1, SEMI-DWARF1; Sub1A, Submergence1A; TIR, transport inhibitor resistant.

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GA is associated with plant responses to flooding, which is
evident in the biosynthesis and signal transduction of GA in
flooded plants.Additionally,exogenous GA relieves the
hazardous effects of flooding on plant growth.Auxin has been
implicated in promoting adventitious rooting by flooded plants.
Summarizing overview of phytohormone-mediated
morphophysiological alteration in flooded plants.
Phytohormone-mediated morphological adaptation in flooded
plants, including coleoptile growth, root architecture, stem
elongation, and leaf petiole movement, is summarized. In
addition, physiological adjustments induced by
phytohormones under flooding are indicated, including water
absorption, anaerobic respiration, cell wall loosening,
photosynthetic pigment, carbohydrate degradation,
programmed cell death, and antioxidant metabolism. ABA,
abscisic acid; BR, brassinosteroid; CHO, carbohydrate; Eth,
ethylene; GA, gibberellic acid; JA, jasmonic acid; SA, salicylic
acid; PS, photosynthetic.

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