CYTOLOGICAL CHARACTERIZATION OF A GIANT STRAIN OF EUGLENA-GRACILIS OBTAINED FROM DARK-STARVED CULTURES

Euglena gracilis green cells were dark-starved for four months. After this period almost the entire population died, while a few giant, viab le cells appeared in the culture. The giantism was maintained after re peated subcultures in growth medium in light or dark conditions. Howev er, the phenomenon was not permanent, and the morphological characteri stics of the wild-type Euglena were gradually restored. In giant cells nuclei enlarged greatly, DNA content increased and the Golgi apparatu s greatly proliferated. Chloroplasts and mitochondria increased in num ber and size and often presented structural modifications when compare d with normal Euglena. Importantly, in the giant cells that were maint ained in darkness in resting or growth conditions chloroplasts persist ed as structured organelles which appeared red-fluorescent under UV il lumination. Whether giantism is a phenotypic or a genotypic change is still debated. In our case, the evolution of this phenomenon, chiefly the enhanced DNA content, suggests that teratism is a multiploid mutat ion with the possibility of a return to the normoploid condition. Cons titutive chloroplasts are present in most algae, except for a few spec ies, among which is Euglena gracilis. The persistence of differentiate d plastids in darkness in giant Euglena is considered to be a return t o an ancestral condition and may, therefore, be phylogenetically impor tant.