[enopod_]

According to the article, at least todays retinal-based photosynthesis is anoxygenic and does not invole carbon fixation. At night, these cells metabolism stops. Chlorophyllic photosynthesis with attached carbon fixation allows the cell to build up starch during the day, which it breathes under the use of oxygen at night, so the cell remains active during the night. Looks like a big evolutionary advantage to me. Also, light is not the limiting factor for plant growth, it‘s usually water or nutrient availability.

[throwawaymaths]

carbon fixation is a completely separate process. in principle you could hook up a sufficiently engineered cell to electrodes and do the carbon fixation part in the dark by supplying it with juice from the mains.

accordingly there is no particular reason for purple photon assimilation to not be attached to carbon fixation... though i suppose as the electron energy levels dont quite match up it might be a schlep to get purples to make sugar.