Abstract
Most photosynthetic organisms including cyanobacteria have two types of protochlorophyllide (Pchlide) reductases; light-dependent Pchlide reductase (LPOR) and nitrogenase-like dark-operative Pchlide reductase (DPOR), which are structurally unrelated. While LPOR was demonstrated to be essential for growth under high light conditions in cyanobacteria, it is still unknown as to the physiological significance of DPOR co-existing with LPOR among wide variety of photosynthetic organisms. We compared growth of a DPOR-lacking mutant (chlL-disruptant) with wild type under various light conditions. Significant growth delay (ca. 8 h) was observed when the dark-grown mutant was transferred to high light conditions (>200 μmol m-2 s-1). During photoautotrophic growth under dark-light cycle (16h-dark/8h-high light), the growth delay of the mutant was obvious in the first light stage though the chlorophyll content was the same as wild type. These results suggested that DPOR is needed for initial adaptation process to high light in cyanobacteria.
