Degeneration and regeneration of chloroplasts in Euglena gracilis grown in the presence of acetate: Ultrastructural evidence

When green cells of Euglena gracilis, strain Z, were light-grown for several months on a solid medium containing an excess of sodium acetate (1.0% instead of the normal 0.1%), some 30% of the cells were colourless. The 'acetate-bleached' organisms, isolated by plating methods and subsequently incubated in the light in a liquid medium, regained the capacity to form chlorophyll in a few days in the absence of any organic carbon source, and within 1-2 weeks in the presence of 0.1% acetate. A number of bleached colonies, however, gave rise to populations in which the delay in pigment synthesis initiation was at least 2 months. Besides numerous paramylum granules and lipid inclusions, the acetate-bleached cells exhibited variably shaped and sized plastids, apparently lacking in ribosomes and showing a deeply disorganized membrane system. In the alga greened in the presence of 0.1% acetate, the pattern of plastidome reorganization was altered; the thylakoids were often unpaired and vesiculated in different degrees, owing primarily to the swelling of the lumen. A complete recovery of normal chloroplast structure occurred only after several weeks of exponential growth. The entire population greened in the absence of acetate constantly showed normal chloroplasts with perfectly reassociated thylakoids and clear partitions.