Plastids of the yellow y-1 strain of Euglena gracilis

A yellow strain, y super(-1), was isolated during heat-induced bleaching of E.gracilis `Z'. The ultrastructure, growth, and carotenoid content of this strain were studied and compared with those of the wild-type Euglena and the heat-bleached `colourless' strain. The yellow, xanthophylls-containing strain y-1 resembles in many respects the etiolated wild-type Euglena, which has lost the ability to form chloroplasts in the light. It represents a transitional stage in the process of progressive degradation of plastids induced by bleaching treatments between the wild-type Euglena and the `colourless' strain. Both bleached strains differ mainly in their carotenoid content formed in the light and especially in the dark, and the size and distribution of undeveloped plastids. In the `yellow bodies' of both strains PLB structure appears in accordance with their plastid nature. The structural changes, appearing in the plastids of bleached Euglena, seem to be at least morphologically very similar to the structural changes occurring in transforming plastids of higher plants.