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Photosynthesis during progressive water stress in interior spruce (Picea glauca (Moench Voss) : physiology and protein composition Eastman, Potter Ann Kathryn
Abstract
Although the stress responses of conifers have been extensively investigated in terms of growth and survival, the ramifications for the perennial photosynthetic apparatus are not well characterized. Coping with excess radiation is particularly important for conifers because the structurally expensive needles usually support multiple seasons of photosynthesis, surviving a range of conditions limiting carbon dioxide fixation. This thesis represents the first detailed characterization of a coordinated set of photosynthetic responses to progressive water stress by young interior spruce (Picea glauca (Moench) Voss XP. engelmanni Parry hybrid complex). Analysis of photosynthesis at the tissue and thylakoid membrane levels revealed a pattern of down-regulation that corresponded generally to that described for other species; however, it differed in that protective mechanisms were initiated during a moderate level of stress. As water potentials declined, an integrated repertoire of mechanisms to cope with excess light energy unfolded. As mild water stress developed at water potentials below -1 MPa, gas exchange measurements indicated stomatal closure and minimal carboxylation. As moderate water stress developed below -1.6 MPa, chlorophyll fluorescence revealed decreases in photochemical efficiency. Nonphotochemical quenching was readily light-saturated in spruce seedlings at any water status; however, quenching increased during moderate water stress at low irradiances, revealing an effect on energy dissipation. Most significantly, electron flow through Photosystem II (PSII) decreased during moderate stress, in contrast to reports for angiosperm species. Details of the thylakoid response to water stress were obtained by immunoquantification of proteins using antibodies to two of the oxygen-evolving enhancer proteins (OEE1 and OEE2), the D l reaction centre protein, cytochrome b₅₅₉, chlorophyll a/b binding proteins, and ATP synthetase at different stress phases defined by physiological criteria. This revealed that only D l levels diminished early in the imposition of water stress; other protein levels were unaffected until the stress became severe. Synthesis of D l , calculated from ³⁵S-methionine labelling of needle proteins, decreased by 80 % in stressed trees whereas it was considerably enhanced in recovering trees, suggesting that D l synthesis was limiting during water stress. A novel observation was that the membrane association of OEE2 with PSII, assessed by susceptibility to removal by detergent, decreased significantly during moderate stress. This occurred before photoinhibition suggesting that this nuclear-encoded protein is intimately involved in PSII down-regulation in spruce, possibly as a component of reversible inactivation.
Item Metadata
Title |
Photosynthesis during progressive water stress in interior spruce (Picea glauca (Moench Voss) : physiology and protein composition
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Creator | |
Publisher |
University of British Columbia
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Date Issued |
1996
|
Description |
Although the stress responses of conifers have been extensively investigated in terms of
growth and survival, the ramifications for the perennial photosynthetic apparatus are not well
characterized. Coping with excess radiation is particularly important for conifers because the
structurally expensive needles usually support multiple seasons of photosynthesis, surviving a
range of conditions limiting carbon dioxide fixation. This thesis represents the first detailed
characterization of a coordinated set of photosynthetic responses to progressive water stress by
young interior spruce (Picea glauca (Moench) Voss XP. engelmanni Parry hybrid complex).
Analysis of photosynthesis at the tissue and thylakoid membrane levels revealed a pattern of
down-regulation that corresponded generally to that described for other species; however, it
differed in that protective mechanisms were initiated during a moderate level of stress.
As water potentials declined, an integrated repertoire of mechanisms to cope with excess
light energy unfolded. As mild water stress developed at water potentials below -1 MPa, gas
exchange measurements indicated stomatal closure and minimal carboxylation. As moderate
water stress developed below -1.6 MPa, chlorophyll fluorescence revealed decreases in
photochemical efficiency. Nonphotochemical quenching was readily light-saturated in spruce
seedlings at any water status; however, quenching increased during moderate water stress at low
irradiances, revealing an effect on energy dissipation. Most significantly, electron flow through
Photosystem II (PSII) decreased during moderate stress, in contrast to reports for angiosperm
species.
Details of the thylakoid response to water stress were obtained by immunoquantification
of proteins using antibodies to two of the oxygen-evolving enhancer proteins (OEE1 and
OEE2), the D l reaction centre protein, cytochrome b₅₅₉, chlorophyll a/b binding proteins, and ATP synthetase at different stress phases defined by physiological criteria. This revealed that
only D l levels diminished early in the imposition of water stress; other protein levels were
unaffected until the stress became severe. Synthesis of D l , calculated from ³⁵S-methionine
labelling of needle proteins, decreased by 80 % in stressed trees whereas it was considerably
enhanced in recovering trees, suggesting that D l synthesis was limiting during water stress. A
novel observation was that the membrane association of OEE2 with PSII, assessed by
susceptibility to removal by detergent, decreased significantly during moderate stress. This
occurred before photoinhibition suggesting that this nuclear-encoded protein is intimately
involved in PSII down-regulation in spruce, possibly as a component of reversible inactivation.
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Extent |
8133048 bytes
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Genre | |
Type | |
File Format |
application/pdf
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Language |
eng
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Date Available |
2009-02-19
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Provider |
Vancouver : University of British Columbia Library
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Rights |
For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use.
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DOI |
10.14288/1.0099053
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URI | |
Degree | |
Program | |
Affiliation | |
Degree Grantor |
University of British Columbia
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Graduation Date |
1996-05
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Campus | |
Scholarly Level |
Graduate
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Aggregated Source Repository |
DSpace
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Item Media
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Rights
For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use.