OXYGENIC PHOTOAUTOTROPHIC GROWTH WITHOUT PHOTOSYSTEM-I

Contrary to the prediction of the Z-scheme model of photosynthesis, ex periments demonstrated that mutants of Chlamydomonas containing photos ystem II (PSII) but lacking photosystem I (PSI) can grow photoautotrop hically with O-2 evolution, using atmospheric CO2 as the sole carbon s ource. Autotrophic photosynthesis by PSI-deficient mutants was stable both under anaerobic conditions and in air (21 percent O-2) at an acti nic intensity of 200 microeinsteins per square meter per second. This PSII photosynthesis, which was sufficient to support cell development and mobility, may also occur in wild-type green algae and higher plant s. The mutants can survive under 2000 microeinsteins per square meter per second with air, although they have less resistance to photoinhibi tion.