DESTRUCTION OF CHLOROPLASTS BY STREPTOMYCIN

Abstract

Exposure to streptomycin (SM) obliterates chloroplasts in seed plants and some algal flagellates. How chloroplasts behave in other organisms is unreported. Certain strains of the flagellate Euglena gracilis offer advantages in studying this process: apochlorotic (“bleached”) races are easily induced, and pure cultures can be maintained indefinitely in simple synthetic media. The oddness of this permanent bleaching is epitomized in Lederberg's remark that SM cures plants of their chloroplasts, and one geneticist, in conversation, has dubbed the phenomenon “mass mutation.” Does SM act on the chloroplast directly or via the nucleus? Other questions come to mind: is the biochemical site of bleaching identical with the site of general lethal, that is, antibiotic action? Photosynthetic pigments in blue-green algae and photosynthetic bacteria are not concentrated in plastids; is their photosynthetic apparatus likewise vulnerable to SM? Which morphological changes mark the destruction of chloroplasts? Are other organelles concomitantly altered or destroyed? May...