Abstract
Singlet oxygen (1O2) causes photoinhibition in plants. To study the mechanism, a reliable detecting and measuring system is necessary. DPAX reacts with 1O2, and increases its fluorescence (Ex = 505 nm, Em = 525 nm). We used 492-nm flash by Xe-PAM for DPAX excitation, and red light for the actinic light to avoid photodecomposition of DPAX. The system made it possible to measure 1O2 generation at chloroplasts under actinic light. Life time and diffusion distance of 1O2 in D2O are shorter than in H2O. 1O2 in D2O was generated as much as in H2O. This indicated that DPAX was closely located at the 1O2 generation site. DCMU suppressed 1O2 generation. But, 1O2 generation restarted when ascorbate and DCIP were added. Also, far-red light application restarted 1O2 generation. 1O2 is generated by transferring excited energy from P680* to 3O2 at PSII. These results indicated that 1O2 is also generated at PSI.
