Possible Roles of Near-infrared Light on the Photosynthesis in Synechocystis sp. PCC6803 under Solar Simulating Artificial Light

Solar simulating light (SSL) has been widely used for evaluating the performance of photovoltaic cells and algal photosynthesis. Green plants and algae utilize chlorophylls, thus, the chlorophyll-targeting light components mostly contribute to photosynthesis. In contrast, near infrared (NIR) light hardly energizes photosynthesis. Since SSL spectrum covers a wide range of light from ultraviolet to NIR, we examined the roles of NIR components in SSL during photosynthetic O 2 evolution in Synechocystis (sp. PCC6803), by selectively and step-wisely eliminating the NIR using several NIR-cut filters. Here, the effects of intact SSL spectrum and the NIR-cut filtered SSL spectra (lacking NIR light greater than 690, 710, 750, or 810 nm) were examined. We observed that the 750 nm shortpass filter lowered the maximal photosynthetic velocity ( P max ), and concomitantly, the Michaelis constant-like value for light intensity ( K j ), whereas no significant change was observed with the 810 nm shortpass filter. We concluded that the 750 (cid:1) 810 nm band may contain the photosynthesis-stimulating NIR component acting differently from the known phenomenon (Emerson effect). In contrast, Synechocystis unexpectedly regained the photosynthetic performance by eliminating all range of NIR ( (cid:6) 710 nm), suggesting that 710 (cid:1) 750 nm far-red band corresponding to the absorption band for bacterial phytochrome is possibly inhibitory to photosynthesis.