Biophysical studies of photosystem II-related recovery processes after a heat pulse in barley seedlings (Hordeum vulgare L.).
Leaves of 7-day-old barley seedlings were subjected to heat pulses at 50 degrees C for 20 or 40s to inhibit partially or fully the oxygen evolution without inducing visible symptoms. By means of biophysical techniques, we investigated the time course and mechanism of photosystem II (PSII) recovery. After the heat treatment, the samples were characterized by typical heat stress symptoms: loss of oxygen evolution activity, strong decrease of Fv/Fm, induction of the K-step in the fluorescence induction transient, emergence of the AT-thermoluminescence-band and a dramatic increase in membrane permeability. In the first 4h in the light following the heat pulse, the AT-band and the K-step disappeared in parallel, indicating the loss of this restricted activity of PSII. This phase was followed by a recovery period, during which PSII-activity was gradually restored in the light. In darkness, no recovery, except for the membrane permeability, was observed. A model is presented that accounts for (i) the damage induced by the heat pulse on the membrane architecture and on the PSII donor side, (ii) the light-dependent removal of the impaired reaction centers from the disorganized membrane, and (iii) the subsequent light-independent restoration of the membrane permeability and the de novo synthesis of the PSII reaction centers in the light.
Tóth
Szilvia Z
SZ
Laboratory of Bioenergetics, University of Geneva, Chemin des Embrouchis 10, CH-1254 Jussy, Switzerland. toth1@etu.unige.ch
Schansker
Gert
G
Kissimon
Judit
J
Kovács
László
L
Garab
Gyozo
G
Strasser
Reto J
RJ
D060387:Ascorbate Peroxidases; D001467:Hordeum / Q000378:metabolism*; D006358:Hot Temperature; D008027:Light; D018384:Oxidative Stress; D010100:Oxygen; D009195:Peroxidase / Q000378:metabolism; D010544:Peroxidases / Q000378:metabolism; D045332:Photosystem II Protein Complex / Q000378:metabolism*; D018515:Plant Leaves / Q000378:metabolism; D036226:Seedlings / Q000378:metabolism; D020524:Thylakoids / Q000378:metabolism; D013997:Time Factors
D045332:Photosystem II Protein Complex; D010544:Peroxidases; C121048:guaiacol peroxidase; D060387:Ascorbate Peroxidases; D009195:Peroxidase; D010100:Oxygen