A Molecular Morphology of Euglena gracilis var. bacillaris*

Abstract

SUMMARY. The structural morphology of Euglena gracilis, particularly the photoreceptors, has been studied by electron microscopy in order to arrive at some structural basis for function. The chloroplast, eye‐spot, and flagella are described and their relationship within the cell discussed. A molecular model for both the chloroplast and eye‐spot are proposed from the available structural and experimental data. The effects of darkness, elevated temperatures, metal depletion, and streptomycin on the cells and structure of the chloroplast are described. In all cases where structural changes occur in the chloroplast they are accompanied by spectral shifts in the absorption spectra of chlorophyll indicative of the appearance of pheophytin. The relationship of the eye‐spot and flagella was considered as a structural unit and the energy for excitation was roughly estimated.

Photoreceptor Structures

“…The calculated value for the number of pigment molecules is HI X 109 for a single rhabdomere. This pigment concentration is similar in order of magnitude to that experimentally determined for the retinal rod and chloroplast in a variety of animal and plant photoreceptors (4,11,12,14,15).…”

MacroMolecular Complexes

“…We have found the algal flagellate Euglena to be uniquely adaptable for experimental studies of the chloroplast structure, since Palade, 1953; Wolken and Sciwertz, 1953;Wolken et al, 1955; Wolken and Mellon, 1956;Wolken, 1956a). E. gracilis when light-grown contains manv green elongated cylindrical chloroplasts 5 to 10/>t in length and 0.5 to 2/>i in diameter.…”

Finer Morphology of Microorganisms

“…This fact also has been verified for several phytoftagellates: Chromulina (16,70) and perhaps Synura (43). On the contrary, the stigma of the phytoflagellates, which has been compared with a parabasal (32), forms an integral part of a chromoplast (7,8,15,16,28,41,67,68,69); but a flagel lum happens to join it at its surface in Chromulina psammobia, as in the case of the spermatozooid of Fucus (44,70).…”