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 ScienceBenedictine University, Lisle, IL

Plants are subject to many stresses

• The main stressors are:Cold Heat Salt

Frost damageHeat damage

Road runoff Irrigation evaporation or drought

Glycine betaine is a molecule that moderates stresses in plants

CH2C

OH

O

NH3C

CH3H3C

Plants are subject to many stresses

• The main stressors are:Cold Heat Salt

Frost damageHeat damage

Road runoff Irrigation evaporation or drought

Wild type TransgenicPlants 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?

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

Unaltere

d experimental ..

.

Group sh

owing uncontro

...

Genetically

altere

d group

Group disp

laying t

he gre...

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What does glycine betaine do for the leaves, flowers and fruits in cold-exposed plants?

What does glycine betaine do?

WT: wild type tomato plants

L1-L9: different lines of transgenic plants

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.

Which photosynthesis process is most effected by ion leakage?

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

Wheth

er cells

can ca

pture

...

Wheth

er the Calvi

n cycle

...

Wheth

er ATP sy

nthase

wi..

Wheth

er electr

ons will

t...

0% 0%0%0%

Plants are subject to many stresses

• The main stressors are:Cold Heat Salt

Frost damageHeat damage

Road runoff Irrigation evaporation or drought

Figure 4. Changes in the oxygen-producing 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.

WT: Wild type tobacco plants and genetically modified tobacco plants

20 25 30 35 40 45 50 550

100

200

300

400

WT

Genetically modified

Temperature of treatment (oC)

Oxyg

en

-evo

lvin

g a

ctiv

ity o

f P

SII

(m

mo

l O

2 m

g-1

Ch

l h

-1)

Which process in photosynthesis produces O2?

A. PS I

B. PS II

C. ATP synthase

D. Light capture

PS I PS II

ATP synth

ase

Light c

apture

0% 0%0%0%

Make two observations from the data

Figure 4. Changes in the oxygen-producing 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.PNG

Which part of the molecule goes through the membrane?

A. Blue box

B. Red oval

Blue box

Red oval

0%0%

Structure of Photosystem II, PDB 2AXT http://en.wikipedia.org/wiki/File:PhotosystemII.PNG

So, the blue box is trans-membrane.

The part below the blue box is associated with the membrane.

Which of the following could explain why increased temperatures decrease PSII activity?

a. Thylakoid membranes become more permeable to ions

b. The chlorophyll breaks down

c. The peripheral proteins lose their ability to bind to the transmembrane proteins

d. Water cannot bind to PSII to form oxygen

Thylakoid m

embranes b

...

The chloro

phyll bre

aks ...

The peripheral p

roteins l

...

Wate

r cannot b

ind to PSI...

0% 0%0%0%

Plants are subject to many stresses

• The main stressors are:Cold Heat Salt

Frost damageHeat damage

Road runoff Irrigation evaporation or drought

Protein sizes are measured in kilodaltons (kDa)a: subunit of 18 kDab: subunit of 23 kDac: subunit of 33 kDa

Make two observations

Which subunit is most stable and likely to be in the membrane?

A. AB. BC. C

A B C

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Which subunit is least stable and likely to be a peripheral subunit?

A. AB. BC. C

A B C

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What does glycine betaine do to protect PSII activity?A. Betaine protects peripheral proteins

again dissociation due to salt

B. Betaine protects transmembrane proteins from dissociation due to salt

C. Betaine promotes dissociation of transmembrane and peripheral proteins in the thylakoids

D. Betaine appers to have no impact on membrane proteins of the thylakoids

Betaine pro

tects perip

her..

Betaine pro

tects tr

ans...

Betaine pro

motes d

issoc..

.

Betaine appers

to have

..

0% 0%0%0%

All the parts need to be together for photosynthesis!

PS II needs to work

Membrane can’t leak so ATP synthase works