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Heat-induced changes of chlorophyll fluorescence in intact leaves correlated with damage of the photosynthetic apparatus
Authors:Ulrich Schreiber  Joseph A Berry
Institution:(1) Department of Plant Biology, Carnegie Institution of Washington, 94305 Stanford, CA, USA;(2) Present address: Department of Biophysics, Huygens Laboratory, State University, Wassenaarseweg 78, Leiden, The Netherlands
Abstract:Methods were developed to measure chlorophyll fluorescence yield of intact leaf tissue during heat treatment under varying conditions of light intensity and photosynthetic activity. Fluorescence yield of a dark-adapted leaf increases by 2- to 3-fold with an increase of temperature into the region where heat-damage occurs. The temperatures of the fluorescence transition correlate well with the temperatures where quantum yield of CO2 fixation is irreversibly depressed. Fluorescence-temperature (F-T) curves allow ranking of different species according to their heat sensitivity. Within a single species acclimation to different growth temperatures is reflected by shifts of the transition temperatures in the F-T curves. When F-T curves are recorded in the steady light states at increasing light intensities, substantial shifts (up to 6°C) of transition temperatures to higher values are observed. Quantum yield measurements of CO2 fixation confirm that hight-light conditions protect from heat-damage. It is suggested that chlorophyll acts as an intrinsic fluorescence probe of the thylakoid membrane and responds to the same changes which cause irreversible denaturation of photosynthetic enzymes.C.I.W.-D.P.B. Publication No. 594
Keywords:Chlorophyll fluorescence  Heat damage  Temperature-sensitivity
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