SINGLET OXYGEN IS NOT PRODUCED IN PHOTOSYSTEM-I UNDER PHOTOINHIBITORYCONDITIONS

Excess illumination of photosynthetic systems brings about the complex functional and structural damage known as photoinhibition. According to the generally accepted and experimentally confirmed model, photoinh ibition involves singlet oxygen production and subsequent oxidative da mage in the photosystem II reaction center. However, it was recently s uggested that singlet oxygen is not necessarily produced in photosyste m II itself but rather in the non-heme iron-containing Fe-S centers of photosystem I (Chung, S.K. & J. Jung, Photochem. Photobiol. 61, 383-3 89, 1995). Contrary to this suggestion, our electron paramagnetic reso nance spectroscopy experiments with the singlet oxygen trap 2,2,6,6-te tramethylpiperidine demonstrate that under photoinhibitory conditions, singlet oxygen is present in thylakoids and photosystem II core compl ex preparations but is not produced in photosystem I particles.