Tougher Plants:
Beating Stress by Protecting
Photosynthesis in Genetically
Modified Plants
Based on a case study by R. Pals-Rylaarsdam and M.L.
Tischler Department of Biological Science
Benedictine University, Lisle, IL
Plants are subject to many stresses
• The main stressors are:
Cold
Heat
Salt
Frost damage
Heat damage
Road runoff
Irrigation evaporation
or drought
Glycine betaine is a molecule that moderates
stresses in plants
Plants are subject to many stresses
• The main stressors are:
Cold
Heat
Salt
Frost damage
Heat damage
Road runoff
Irrigation evaporation
or drought
Wild type
Transgenic
Plants were exposed to 3C
for 7 days, then transferred
to the warm greenhouse.
NB: This figure is a simulation of a figure in the original article.
What does wild type mean?
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A. Unaltered experimental
group
B. Group showing
uncontrolled or “wild”
grow
C. Genetically altered group
D. Group displaying the
greatest variance in an
observed trait
What does glycine betaine do for the leaves,
flowers and fruits in cold-exposed plants?
What does glycine betaine do?
Figure 3. Effects of chilling on various
growth parameters. Five-week-old
greenhouse-grown wild type and
independent homozygous transgenic lines
(L1, L5) were chilled (3°C) for 5 days, then
returned to greenhouse.
WT: wild type
tomato plants
L1-L9: different
lines of transgenic
plants
Which photosynthesis process is most effected
by ion leakage?
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A. Whether cells can capture
light
B. Whether the Calvin cycle
will function
C. Whether ATP synthase will
function
D. Whether electrons will
transfer from PS II
Plants are subject to many stresses
• The main stressors are:
Cold
Heat
Salt
Frost damage
Heat damage
Road runoff
Irrigation evaporation
or drought
Figure 4. Changes in the oxygenproducing activity of PSII determined
with thylakoid membranes isolated
from leaves after exposed to different
temperatures 25, 30, 35, 40, 45, or
50°C in the chambers for 4 h, in wild
type and transgenic plants. The values
are mean + SE of three independent
experiments.
Oxygen-evolving activity of PSII
(mmol O2 mg-1 Chl h-1)
400
300
200
100
WT
Genetically modified
0
20
25
30
35
40
Temperature of treatment
45
(oC)
50
55
WT: Wild type tobacco
plants and genetically
modified tobacco plants
Which process in photosynthesis produces O2?
PS I
PS II
ATP synthase
Light capture
0%
0%
pt
ur
e
ca
L ig
ht
AT
P
sy
nt
ha
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e
II
0%
PS
I
0%
PS
A.
B.
C.
D.
Make two
observations from
the data
Figure 4. Changes in the oxygenproducing activity of PSII
determined with thylakoid
membranes isolated from leaves
after exposed to different
temperatures 25, 30, 35, 40, 45, or
50°C in the chambers for 4 h, in wild
type and transgenic plants. The
values are mean + SE of three
independent experiments.
Photosystem II
Structure of Photosystem II, PDB 2AXT
http://en.wikipedia.org/wiki/File:PhotosystemII.PN
Which part of the molecule goes through the
membrane?
A. Blue box
B. Red oval
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x
0%
So, the blue box is
trans-membrane.
The part below the
blue box is
associated with
the membrane.
Structure of Photosystem II, PDB 2AXT
http://en.wikipedia.org/wiki/File:PhotosystemII.PN
G
Which of the following could explain why
increased temperatures decrease PSII activity?
to
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d.
yla
b.
c.
Thylakoid membranes become
more permeable to ions
The chlorophyll breaks down
The peripheral proteins lose
their ability to bind to the
transmembrane proteins
Water cannot bind to PSII to
form oxygen
Th
a.
Plants are subject to many stresses
• The main stressors are:
Cold
Heat
Salt
Frost damage
Heat damage
Road runoff
Irrigation evaporation
or drought
Protein sizes are
measured in
kilodaltons (kDa)
a: subunit of 18 kDa
b: subunit of 23 kDa
c: subunit of 33 kDa
Make two
observations
Which subunit is most stable and likely to
be in the membrane?
A. A
B. B
C. C
0%
A
0%
B
0%
C
Which subunit is least stable and likely to
be a peripheral subunit?
A. A
B. B
C. C
0%
C
0%
B
A
0%
What does glycine betaine do to protect PSII activity?
ns
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D.
e
C.
ta
in
B.
Betaine protects peripheral proteins
again dissociation due to salt
Betaine protects transmembrane
proteins from dissociation due to
salt
Betaine promotes dissociation of
transmembrane and peripheral
proteins in the thylakoids
Betaine appers to have no impact on
membrane proteins of the
thylakoids
Be
A.
All the parts need to be together for photosynthesis!
PS II needs to work
Membrane can’t
leak so ATP
synthase works