Aspects of structure and photosynthetic competence ofEuglena plastids under conditions of greening and degreening

Summary

Dark-grownEuglena cells were exposed to light at both their late stationary phase of growth (“old cells”), and at their late exponential phase (“young cells”). Chlorophyll accumulation was faster and photosynthetic oxygen evolution was detected earlier in the “young” cells. Photosystem I activity was measured at early stages of greening in both “young” and “old” cells. Rate of activity on a chlorophyll basis at these early stages was 6–7 times higher than the constant levels of the late stages. Photosystem II activity developed with illumination and showed a long lag period in “old” cells. In cells returned from light to dark, after seven generations in the dark, photosystem I was seven times more active on a chlorophyll basis than in light-grown cells. Photosystem II activity inceased up to four generations in the dark and decreased thereafter. Chlorophyll was diluted among progeny, whereas oxygen evolution did not show a similar dilution pattern in the dark. Chloroplasts lost their typical structure and were transformed into proplastids. Prolamellar bodies within the transformed plastids were observed after 2–4 generations in the dark. Non-dividing cells, in contrast to the dividing ones, kept their chlorophyll, their ability to evolve oxygen, and their plastidial structure over long periods.