TRANSFORMATION OF THE PHOTOACOUSTIC SIGNAL AFTER TREATMENT OF BARLEY LEAVES WITH METHYLVIOLOGEN OR HIGH-TEMPERATURES

The photoacoustic (PA) signal at the modulation frequency of 35 Hz was studied in MV-treated barley leaves or leaves preheated at different temperatures, Saturating illumination enhanced the magnitude of the PA signal in MV-treated leaves in contrast with the opposite result usua lly found in untreated intact leaves where saturating illumination abo lishes the photobaric component of the PA signal due to oxygen evoluti on and thus decreases the total PA signal, A linear relationship was f ound between the changes induced by continuous background light in the negative response of PA signal to saturating light in intact leaves a nd in the positive response in MV-treated leaves, A linear relationshi p was also observed in MV-treated leaves between the positive changes in the PA signal and the changes in the rate of electron transport thr ough photosystem II (PSII) calculated from chlorophyll fluorescence da ta, The conclusion was drawn that only the thermal component contribut es to the PA signal measured at low modulated frequency in MV-treated leaves because the enhanced O-2 uptake provides a zero net oxygen exch ange by superimposing with O-2 evolution. The leaves preheated at temp eratures above 43 degrees C demonstrated the positive response of the PA signal to saturating light at 35 Hz. In leaves preheated at 41.5 de grees C, the first and second saturating pulses induced the enhancemen t of PA signal, whereas other pulses decreased the PA signal due to on set of oxygen evolution. The energy storage activity measured in the a bsence of oxygen evolution in heat-treated leaves is proposed to be as sociated with cyclic electron transport activities around PSII and PSI .