Photoinhibition of the CAM succulent Opuntia basilaris growing in Death Valley: evidence from 77K fluorescence and quantum yield |
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Authors: | W W Adams III S D Smith C B Osmond |
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Institution: | (1) Biological Sciences Center, Desert Research Institute, University of Nevada System, PO Box 60220, 89506 Reno, NV, USA;(2) Present address: Department of Environmental Biology, Research School of Biological Sciences, GPO Box 475, 2601 Canberra, ACT, Australia;(3) Present address: Department of Biological Sciences, University of Nevada, 89514 Las Vegas, NV, USA |
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Abstract: | Summary Diurnal measurements of low temperature (77K) fluorescence at 690 nm (PS II) from north, south, east, and west facing cladode surfaces of Opuntia basilaris in Death Valley, California were made on six occasions during 1985. The absolute levels of F
o(instantaneous fluorescence) and F
m(maximum fluorescence), as well as the ratio F
v/F
m(variable fluorescence, F
m-F
o, over maximum fluorescence), were greater in the north face relative to the other faces. Diurnal decreases in F
o, F
mand F
v/F
mwere found concomitant with increases in incident photon flux area density (PFD). F
v/F
mwas fairly low throughout the year, indicative of photoinhibition, but became somewhat elevated after a spring rain. In early fall the quantum yield of the south face was considerably depressed relative to that of the north face, and corresponding differences were observed in F
v/F
m. A decrease in PFD during growth of glasshouse plants led to an increase in chlorophyll concentration, F
oand F
m, but not F
v/F
m. Although there was some variability in the quantum yield of well watered glasshouse cladodes, a correlation was found between quantum yield and the light and CO2 saturated rate of photosynthesis. When O. basilaris was water stressed under glasshouse conditions, reductions in quantum yield, F
m, and F
v/F
mwere observed. Reductions in F
v/F
malways indicated a reduced quantum yield, although the converse was not necessarily so in well watered glasshouse plants. The results of this study indicate that O. basilaris is likely to experience photoinhibition throughout much of its life in Death Valley.Abbreviations
CAM
crassulacean acid metabolism
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MPa
megapascal
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PFD
photon flux area density
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PS II
photosystem II
-
vater potential
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F
o
instantaneous fluorescence
-
F
m
maximum fluoescence
-
F
o
variable fluorescence |
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Keywords: | Photoinhibition Crassulacean acid metabolism (CAM) 77K fluorescence Quantum yield Stress physiology |
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