The chloroplasts of Euglena may have evolved from symbiotic green algae

Abstract

It is proposed that the chloroplasts of Euglena have arisen from the progressive reduction of endosymbiotic green algae. The theory is supported by the presence of a third membrane around the chloroplasts of Euglena which is not endoplasmic reticulum (ER) in origin and may be derived from the plasmalemma of the original symbiont. In addition, Euglena is the only organism in which chloroplast loss can be induced experimentally. Dinoflagellate chloroplasts are also surrounded by three membranes, and it is proposed that they too evolved from symbiotic eucaryotic algae.