Abstract
Most phototrophic organisms including cyanobacteria synthesize chlorophyll by the two different protochlorophyllide (Pchlide) reductases; one is light-independent reductase (DPOR) and the other is light-dependent reductase (LPOR). We report here differentiation of the two Pchlide reductases in response to the environmental oxygen concentration in the cyanobacterium Plectonema boryanum.
A DPOR-less mutant (YFC2), an LPOR-less mutant (YFP12) and the wild type of P. boryanum were cultivated photoautotrophically bubbling with mixture gas (N2-2%CO2) containing various amount of oxygen (0-21%) under high light conditions. While YFC2 grew as well as the wild type in all examined conditions, YFP12 grew only under the oxygen concentrations less than 5% with the maximal growth rate (ca 62% of the wild type) at 0% O2. This result indicated that LPOR is essential for growth under the conditions with oxygen more than 5%. An evolutionary aspect of chlorophyll biosynthesis will be also discussed.
