The Plastid System of Normal and Bleached Euglena gracilis*

Abstract

SYNOPSIS. The plastid system of “normal”Euglena gracilis strain Z was found to be extremely unstable. Under normal culture conditions in the light about 1 or 2% of the cells were found to have lost spontaneously the capacity to green on further culturing. Cells treated with streptomycin, heat or U.V. all lost the capacity to green on further culturing. Bleached cells whether appearing spontaneously or by induction with streptomycin, heat, or U.V. light, were all found to possess within them organelles which were identified as proplastids. The proplastids of some “bleached” strains were capable of synthesizing porphyrins when grown in a standard culture medium. Others synthesized porphyrins only after the addition of delta‐aminolevulinic acid to their medium, while proplastids of still other strains could not synthesize porphyrins from this precursor. Normal cells when grown in total darkness were found to possess proplastids morphologically identical with those of the bleached strains. Upon exposure to light the proplastids enlarged and greened. In cells which grew under continuous light the plastid system appeared as an interconnected system of tubules. Cells maintained on a schedule of 12‐hour light and 12‐hour dark had plastids which were detached from each other.

Behaviour of proplastids and their nucleoids in dark-organotrophically grown cells ofEuglena gracilistransferred to an inorganic medium

“…It may be presumed that some substance(s) is transported through the site of association between the nucleus and plastid. The morphology of chloroplasts in association with the nucleus in Euglena cells has been reported previously (Gibor & Granick, 1962: Calvayrac & Lefort-Tran, 1976Ledoigt and Calvayrac, 1979). Our recent studies showed that in an early phase of the cell cycle of Euglena gracilis Z in synchronized cultures under photo-organotrophic conditions, chloroplasts temporarily conjoin to form a single giant body, which comes into association with the nucleus.…”

Effect of Light on Glucose Utilization by Euglena gracilis

“…As observed before for growth inhibition the effect on glucose uptake is lower in mutants than in wild-type, and in W3BUL compared to W3ZUD (Table IV). ['4Cjglucose (20 nCi/ml) was added and the flasks incubated in darkness (-) or under different light intensities (---). The amount ofglucose remaining in the medium was measured every day.…”

Photoinduced Carotenogenesis in Chlorotic Euglena gracilis

“…In Euglena carotenogenesis parallels chlorophyll synthesis in light-synchronized cultures (2). However, when chlorophyll synthesis is blocked by mutagenic agents, carotenogenesis still occurs and is stimulated by light (9). Bleached mutants generally lack the xanthophylls found in wild-type Euglena, and the carotenes (,-carotene, i-carotene, and phytofluene) occur at reduced levels (13).…”