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(P) Flooding (Hypoxic) Stress - Coggle Diagram
(P) Flooding (Hypoxic) Stress
Plants have many MODIFICATIONS to cope with hypoxic/anoxic stress. What are they?
Adjustment growth and development
roots
reduction of O2 loss by
suberin and lignin deposition: thicker root hypodermis
production of
cortex aerenchyma (cavities, lacunas) to facilitate O2 transport to the roots :skull_and_crossbones:
adventitious roots
(hypocotyl or stem)
shallow root system
pneumatophores (negative geotropy)
lenticels (porous tissue with large intercellular space) in the periderm for gas exchange
shoots
Stem elongation
‘Escape’ strategy - deep water rice
internodal elongation and adventitious root formation
Hormonal regulation:
ethylene :arrow_up:
ABA :arrow_down:
production & sensitivity to GA :arrow_up:
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Alternative strategy:
Quiescence’ strategy
GA signalling and thus elongation are inhibited by the ethylene-induced action of a SUBMERGENCE gene (
SUB1A-1
) on the growth-inhibiting genes SLENDER RICE-1 (SLR1) and SLR LIKE-1 (SLRL1).
Metabolism
during short-term acclimation to hypoxia and anoxia plants generate ATP mainly via
glycolysis
aka
Pasteur effect
net production of
2
ATP/glucose
need to regenerate NAD+
fermentation!
starts with lactate production but
ATP depletion leads to
no active H+ transport into apoplast or vacuoles
proton leakage
in cytosol -> low pH
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Selective gene expression and translation
gene expression generally limited
70% reduction in protein synthesis, a massive ATP consumer! (
SnRK1
inhibits ribosomal protein gene expression)
but: an important subset of genes/proteins is induced:
Sucrose and starch degradation
Glycolysis
Ethanol fermentation
selective
induction transcription + more
efficient
translation:
mRNAs recruited to ‘polysomes’
. transcription: cis-regulatory elements
ARE
: anaerobic response element - in combination with G-box
Also oxygen ‘sensing’ mechanism (similar to animals):
ERF-VII
transcription factors
NORMALLY: oxidation-triggered degradation but in HYPOXIA: stabilisation & nuclear translocation
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Post-transcriptional regulation
stress granules (storage) and processing (P) bodies (degradation)
Ethylene
promotes long-term
acclimation
-responses (aerenchyma formation, stem elongation) in tolerant species
Ethylene synthesis:
Met
SAM/AdoMet
ACC synthase
ACC
ACC
oxidase
Ethylene
secondary messenger
Ca2+, phosphorylation
and other mechanisms are also involved in ethylene-mediated hypoxia signaling
also causes epinastic growth :arrow_down: in sensitive species:
synthesis + transport ACC in hypoxic roots, then synthesis ethylene in stems and leaves -> expansion adaxial petiole cells
(not wilting, no loss of turgor)