Zusammenfassung der Ressource
Biol 526 Exam 2 - Ice
- What is cold? Free atmosphere
conditions that deviate substantially
(negatively) from optimum
temperatures for growth (varies by
species)
- Cold Hardiness - the ability of a
plant to adapt to and withstand
freezing temperatures at a
structural or cellular level
- Adaptations
- Avoidance - physical attributes
of a plant that determine if,
when, or where ice forms
within the plant (ice nucleators,
supercooling, ice barriers)
- Tolerance - biochemical
adaptations brought about or
regulated by a specific set of
genes (membrane changes,
cryoprotective compounds,
compatible solute and sugar
production)
- Acclimation - "nonheritable"
changes in gene expression and
protein accumulation that enable
the plant to tolerate dehyrdative
stress during freezing temps
- Acute Stress -
single freezing
event
- Chronic Stress -
prolonged period of
freezing or ice
encasement
- Multiple components: time,
latitude/elevation, and
temperature (gradual vs.
extreme)
- Evolutionary
adaptations for
a cold-adapted
genotype
- Freezing resistance -
must resist local low
temperature extremes
- Fine-tuning of plant
phenology - "seasonality"
avoids damaging freezing
temperatures in fall/spring
- Plant stature -
short/tall as is
environmentally
appropriate
- Experiments
- Overexpression of Chinese
cabbage ICE1 gene
- Plant - Chinese
Cabbage
(Brassica
campestris) &
rice host
- Conditions - 20 day old
rice seedlings exposed
to 4°C & -2°C for 48 h,
respectively, then 10
days of recovery at
normal temps
- Treatments - ICE1 homolog (BcICE1)
from Chinese cabbage was
overexpressed with a ubiquitin
promoter to assess freezing
tolerance. Wild type rice and mainly
two transgenic lines with the BcICE1
gene (L03 & L07) were observed.
- What did they look for? To see if the
overexpression of an ICE! gene from Chinese
cabbage could increase the freezing tolerance
of rice in an ICE1-CBF cold responsive signal
pathway,
- What did they measure?
Survival rates, electrolyte
leakage, the expression of COR
genes, and the relative content
of proline, soluble sugars, MDA,
and chlorophyll.
- Results - The overexpression of the BcICE1
gene in rice increased the survival rate, proline
content, and sugar content. Electrolyte leakage
and chlorophyll were better with the gene
present, and there was a drastic increase in
the production of COR genes.
- Mutational Evidence for the
Critical Role of CBF
Transcription Factors
- Plant -
Arabidopsis
- Conditions - Cold
acclimation (4° C)
for 7 days, some
trials exposed to -7°
C for 1 hr, 23° C for
recovery
- Treatments - CRISPR/Cas 9
system to generate single, double
and triple CBF mutants,
electrolyte leakage assay,
freezing survival assay, & RNA
sequencing assay
- What did they look for? The
role of CBF proteins in
freezing tolerance, plant
development, and
confirmation that COR genes
are regulated by CBF
transcription factors
- What did they measure?
Germination rates, growth, and
flowering of mutants, survival rate
and electrolyte leakage, COR gene
expression, and the regulation of
CBF-activated genes
- Results - Plant development worsened, electrolyte leakage was
much greater, and COR genes were not expressed in the
mutants compared to wild type due to the accumulation of
DELLA proteins via reduction of GA, indicating that CBF genes
play a critical role in freezing tolerance; CBF genes are redundant,
however, CBF2 is more important in cold acclimation
- Rice mutants deficient in omega-3
fatty acid desaturase (FAD8)
- Plant - rice
(Oryza sativa L..)
- Treatments - 3 T-DNA insertional
knockout mutants of FAD8
(osfad8-Ex3, osfad8-Ex7, osfad8-int4)
and wildtype for control
- Conditions - 5 days
at 28°C and 4°C
- What did they
look for?
Changes in
fatty-acid
composition and
changes in
thylakoid
membrane
fluidity to
determine if the
photosynthetic
mechanism was
intact
- Results - At low
temps, 18:3/18:2
ratio decreased in
mutants (lost their
ability to
desaturate),
photosystem
efficiency was
much lower in the
mutants, more
degradation of D1
in the mutants,
and less light
absorbed in the
mutants (failure to
acclimate to light
due to decreased
desaturation)
- What did they
measure? 18:3/18:2
ratio and DBI
(double bond index)
in chloroplast
membrane lipids
(MGDG, DGDG,
SQDG, & PG),
chlorophyll
fluorescence,
degradation of D1
proteins, and PS1
activity (amount of
P700)
- Plant traits
co-vary with
altitude
- Plant - 701
species in the
Swiss Alps
- Conditions - 5 sites in the Swiss Alps, transects in
grasslands and forests, 120 vegetative plots total
- Treatments - none, mountain altitude was
a substitution for temperature change
- What did they look for? Variations
of 13 plant traits along altitudinal
gradients (mainly life form, leaf
morphology, & reproduction)
- What did they measure? Applied
PCA exploratory tool to compare
variables with one another at the
same time to look for trends
- Results - 11/13 traits
showed trends, mainly
plant size decreases and
vegetative reproduction
is more frequent as
altitude increases
- Cold Stress Regulation
of Gene Expression
(Arabidopsis)
- Step One: Cold
temperatures reduce
membrane fluidity,
increased rigidity
- Step Two: Membrane
rigidification, ABA, or ROS
activate Ca2+ channels,
increasing Ca2+ in the cytosol
- Step Three: Increased levels of Ca2+
activate protein kinases, which
activate ICE proteins (Inducer of CBF
Expression) transcription factors
- Step Four: ICE proteins
induce the expression
of CBF genes (C-repeat
binding factor)
- Step Five: CBF
proteins induce the
expression of COR
genes (Cold
Responsive)
- Step Six: COR proteins
alter the physiology of
the plant for cold
acclimation