Transcript Tilele Stevens_Botany Thesis Project

Role of Xanthophyll Cycle in
Non-Photochemical Energy
Dissipation in C3 & C4
Alloteropsis Grasses Subject to
Drought
By: Tilele Stevens
Supervisors:
Dr. Brad Ripley &
Matthew Gilbert
ALLOTEROPSIS SEMIALATA
Widespread grass, family Paniceae
Unusual because it is the only known species that
has subtypes with different photosynthetic
pathways
http://www.palaeobiology.org.uk
RESPONSES TO LIGHT
Photorespiration
Photoinhibition
Thermal energy
dissipation
Absorbed
Light
energy
ATP and
NADPH
CO2 fixation
Mehler reaction
Chlorophyll
fluorescence
Haasbroek et al., (2005)
CO2 assimilation reduced due
to stomatal closure
Photorespiration
Photoinhibition
Thermal energy
dissipation
Absorbed
Light
energy
ATP and
NADPH
CO2 fixation
Mehler reaction
Chlorophyll
fluorescence
Haasbroek et al., (2005)
PHOTORESPIRATION
Waste of energy
OR
http://www.marietta.edu/
Occurs in C3 plants
May be used in
photoprotection
It uses up excess
energy
C4 PATHWAY
C4 plants concentrate
CO2 in their bundle
sheath
C4 plants require an
alternative pathway to
dissipate energy when
under stress
www.botany.hawaii.edu
Photorespiration
Photoinhibition
Thermal energy
dissipation
Might use
xanthophyll
cycle???
Haasbroek et al., (2005)
Absorbed
Light
energy
ATP and
NADPH
CO2 fixation
Mehler reaction
Chlorophyll
fluorescence
XANTHOPHYLL CYCLE
Discovered by Demmig-Adams and Adams (1986)
Adams et al, (2004)
ROLE OF ZEAXANTHIN
Binds to light
harvesting antenna
proteins
Causes protein
conformational changes
that result in heat
dissipation
www.springerlink.com
SIGNIFICANCE
www.illusionmasks.com/images3/maize.jpg
www.ldd.go.th/EFiles_JPG/sugarcane.jpg
C4 plants may be vulnerable to stressful conditions
Many crops are C4
HYPOTHESIS
When exposed to stressful high light intensity C4
plants dissipate more energy as heat (xanthophyll
cycle) compared to C3 plants because they have
lower levels of photorespiration
METHODS AND MATERIALS
10 C3 and 10 C4
5 watered (controls) and 5 drought stressed (16 days)
Soil water content measured using a Theta Probe
Fluorescence and photosynthesis measurements were
carried out using a LiCor 6400
Leaf water potential measured using a Scholander
Pressure Bomb
Leaves harvested and
frozen in liquid nitrogen
(-70oC)
HPLC Machine
Leaves crushed in acetone,
centrifuged & analysed
using HPLC
http://www.easy2source.com
HPLC solvent used
acetonitrile:methanol:Tris
HCl (85:25:4)
Results analysed using
Anova and Tukey
RESULTS
0.0
-0.1
-0.2
-0.3
-0.4
-0.5
-0.6
-0.7
-0.8
C4 Control
C4 Drought
Stressed
C3 Control
C4 Control
C3 Drought
Stressed
C4 Drought
Stressed
0.0
-0.5
a
a
-1.0
b
b
LWP (MPa)
Soil Water Content (MPa)
C3 Control
C3 Drought
Stressed
-1.5
ab
-2.0
-2.5
a
-3.0
bc
c
-3.5
-4.0
Soil Water Content of the Grasses at Time of Harvest
Variation with Leaf Water Potential
Subtype = 0.32
Subtype = 0.018
Drought = 0.000094
Drought = 0.000071
Subtype*Drought = 0.29
Subtype*Drought = 0.93
Fv/Fm
Recovery fluorescence
measurements
Fv/FM
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
There was no
permanent
photoinhibition
C3 Control
C4 Control
C3 Drought
Stressed
Variation in the Efficiency of PSII
C4 Drought
Stressed
Subtype = 0.018
Drought = 0.00003
Subtype*Drought = 0.63
(m mol CO2 m-2 S-1)
Photosynthetic Rate
18
a
16
14
a
12
10
b
8
6
b
4
2
0
C3 Control
C4 Control
C3 Drought Stressed
C4 Drought Stressed
Variation in the Photosynthetic rates
Subtype = 0.02
Drought = 0.011
Stomatal Conductance
Subtype*Drought = 0.038
0.40
0.35
0.30
0.25
a
0.20
0.15
b
0.10
b
b
C3 Drought
Stressed
C4 Drought
Stressed
0.05
0.00
C3 Control
C4 Control
Variation in Stomatal Conductance
Subtype = 0.0003
Drought = 0.000048
Subtype*Drought = 0.22
ETR (m mol m-2 S-1)
140
120
a
b
100
80
bc
c
60
40
20
0
C3 Control
C4 Control
C3 Drought
Stressed
C4 Drought
Stressed
Variation in the Electron Transport Chain
Subtype = 0.0003
Drought = 0.00005
Subtype*Drought = 0.23
j PSII
0.20
0.15
a
b
bc
0.10
c
0.05
0.00
C3 Control
C4 Control
C3 Drought
Stressed
C4 Drought
Stressed
Variation in Quantum PSII Efficiency
Subtype = 0. 00086
Drought = 0.012
Subtype*Drought = 0.21
Conc of Zeaxanthin (mmol/ g fresh
weight)
3.0
a
2.5
2.0
b
b
1.5
1.0
b
0.5
0.0
C3 Control
C4 Control
C3 Drought Stressed C4 Drought Stressed
The Concentration of Zeaxanthin in the Grasses
Zeaxanthin Conc
4.0
3.5
3.0
2.5
C3
2.0
C4
1.5
1.0
0.5
0.0
0.15
0.20
0.25
0.30
0.35
0.40
0.45
0.50
NPQ (Heat Energy)
Plot of NPQ vs Zeaxanthin Concentration
As heat energy increases so does
the concentration of zeaxanthin
DISCUSSION
In C3 Plants
Photorespiration
Photoinhibition
Thermal energy
dissipation
Absorbed
Light
energy
ATP and
NADPH
CO2 fixation
Mehler reaction
Chlorophyll
fluorescence
Haasbroek et al., (2005)
DISCUSSION
In C4 Plants
Photorespiration
Photoinhibition
Thermal energy
dissipation
Absorbed
Light
energy
ATP and
NADPH
CO2 fixation
Mehler reaction
Chlorophyll
fluorescence
Haasbroek et al., (2005)
CONCLUSIONS
Because C4 plants have reduced
photorespiration they have to use
alternative pathways to dissipate excess
energy
C4 have a higher concentration of
Zeaxanthin pigments compared to C3
grasses
When stressed C4 plants dissipate more
thermal heat compared to C3 plants
www.ldd.go.th/EFiles_JPG/s
ugar-cane.jpg
Thank You
REFERENCES
Demmig – Adams, A., Linking the xanthophyll cycle with thermal energy
dissipation, Photosynthesis Research, Vol 76: 73-80, 2003.
Gilbert M. (2006): Gravimetric Soil Water Content, Botany Department, Rhodes
University, Grahamstown.
Finazzi G., Johnson G.N., Dall’Osto L., Joliot P., Wollman, F.A., Bassi, R., A zeaxanthin
independent nonphotochemical quenching mechanism localized in the photosystem II core
complex, PNAS, Vol 101:no. 33 12375-12380, 2004
Jahns P., Krause G.H., Xanthophyll cycle and energy-dependent fluorescence quenching in
leaves from pea plants grown under intermittent light, Planta, Vol. 192: 176-182, 1994.
Long S.P., (1999): Environmental Responses in C4 Plant Biology by Sage, R.F., Monson,
R.K., (Eds), Academic Press, London.
REFERENCES
Ripley B.S., (2001): The Ecophysiology of selected coastal dune pioneer plants of the
Eastern Cape, Rhodes University, Grahamstown.
Ripley B.S. (2006): Botany 301 Ecophysiology Notes, Botany
Department, Rhodes University, Grahamstown.
Schindler C., Lichtenthanler H.K., Photosynthetic CO2-assimilation, chlorophyll
fluorescence and zeaxanthin accumulation in field grown maple trees in the course of a
sunny and cloudy day, Journal of Plant Physiology, Vol. 148: 399-412, 1996.
Taiz L., Zeiger E., (2002): Plant Physiology 3rd Edition, Sinauer Associates Inc. Publishers,
Massachusetts.
Van Outshoorn F., (2002): Guide to Grasses of Southern Africa, Briza
Publications, Pretoria.
Web refs:
www.palaeobiology.org.uk
www.marietta.edu/
Questions?
Subtype = 0.98
Drought = 0.0059
Subtype*Drought = 0.52
0.50
0.40
ab
a
0.30
qP
bc
c
0.20
0.10
0.00
C3 Control
C4 Control
C3 Drought Stressed C4 Drought Stressed
Variation of qP
DISCUSSION
Drought stressed plants have reduced ETR and
photosynthetic rates
Therefore have more excess energy
Dissipate excess energy as heat to prevent photoinhibition
C4 plants have reduced photorespiration compared to
C3 grasses
C4 have more zeaxanthin and dissipate more heat
energy under stress