The effects of temperature acclimation on the photoinhibitory responses of Ulva rotundata Blid. |
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Authors: | Linda A Franklin |
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Institution: | (1) Duke University Marine Laboratory, 28516-9721 Beaufort, NC, USA;(2) Present address: Research School of Biological Sciences, Institute of Advanced Studies, The Australian National University, 2601 Canberra, ACT, Australia |
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Abstract: | The effect of acclimation to 25, 18, or 10° C on the relationship between photoprotection and photodamage was tested in low-light-grown (80 mol · m–2 · s–1) Ulva rotundata Blid. exposed to several higher irradiances at the acclimation temperature. Changes in chlorophyll fluorescence parameters (minimum fluorescence, F0, and the ratio of variable to maximum fluorescence, Fv/Fm, measured after 5 min darkness) were monitored during 5 h transfers to 350, 850, and 1700 mol · m–2 · s–1, and during recovery after 1- or 5-h treatments. At all temperatures, rate of onset and final extent of photoinhibition, measured by a decrease in Fv/Fm, increased with increasing irradiance. At a given photoinhibitory irradiance, rate of onset was most rapid at 10 ° C, but the extent was temperature-independent. Recovery rates from mild light stress were similar at all temperatures, but recovery from the most extreme photoinhibitory treatment lagged 2 h at 10° C. De-epoxidation of xanthophyll-cycle components proceeded faster and to a lower epoxidation status at 25° C, but there was little difference in the pool size among the three growth conditions. Using chloramphenicol to inhibit chloroplast protein synthesis and dithiothreitol to inhibit violaxanthin de-epoxidation, it was shown that at the lowest light treatment given, the extent of photoinhibition could be attributed both to greater amounts of photodamage and to greater zeaxanthin-related photoprotection at 25 than at 10° C. While these two mechanisms for high-light-induced loss of photosynthetic efficiency were operating at 10° C, there was evidence for a relatively greater proportion of zeaxanthin-unrelated photoprotection at the low temperature. This photoprotective mechanism is related to a rapidly reversible increase in F0 and is insentivite to both chloramphenicol and dithiothreitol.Abbreviations and Symbol CAP
chloramphenicol
- DTT
dihiothreitol
- F0, Fm, Fv
minimum, maximum, and variable fluorescence
-
quantum yield
This research was conducted in partial fulfillment of the requirements for the Ph. D. degree in the Department of Botany, Duke University. The author wishes to thank E.-M. Aro, W.J. Henley, G. Levavasseur, C.B. Osmond, and J. Ramus for helpful discussions, and C. Lovelock for pigment standards. Funding was provided by Grants-in-Aid of Research from Sigma Xi and the Phycological Society of America, and a Lynde and Harry Bradley Foundation Fellowship to L.A.F., and National Science Foundation grant OCE-8812157 to C.B.O. and J.R. |
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Keywords: | Chlorophyll fluorescence Photoinhibition Photoprotection Temperature Ulva Xanthophyll cycle |
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