S U M M A R YDuring chloroplast development, the large increases in ribulose diphosphate carboxylase (RUDPCase) activity and cytochrome 5 5 2 concentration follow the pattern of chlorophyll synthesis, in that the formation of these two enzymes is inhibited by streptomycin (Sm) and by chloramphenicol (Cm) beyond 12 h of development. Neither enzyme can be detected in W,BUL, a mutant of Euglena in which chloroplasts and chloroplast DNA are undetectable. In contrast, the NADP-linked triose phosphate dehydrogenase (NADP-TPDase), another plastidlocalized enzyme, increases in activity without the 12 h lag normally observed for chlorophyll synthesis; this increase in activity is not inhibited by Sm and Cm, but is inhibited by cycloheximide, an antibiotic which acts on 87 S cytoplasmic ribosomes. NADP-TPDase activity is present at the same level in W,BUL as in the dark-grown wild-type organisms. These data are interpreted to mean that NADP-TPDase is coded in the nuclear DNA, and is translated on 8 7 s cytoplasmic ribosomes. The sensitivity of the increase in cytochrome 552 and RUDPCase activities to Sm and Cm indicates that they are translated, at least in part, on the 68 S ribosomes of the chloroplast. Thus, chloroplast differentiation in Euglena is dependent upon information and synthetic machinery from both the plastid and the rest of the cell. Since total cellular protein does not change significantly during chloroplast development in resting cells, we conclude that protein turnover probably occurs.

The concentration of streptomycin (Sm) which selectively inhibits light-induced chloroplast development in non-dividing Euglena is the same as that which induces the loss of green-colony forming ability in dividing organisms. This concentration of Sm has no effect on division or viability. Chlorophyll synthesis is insensitive to streptomycin for the first 1 2 h of development but is strongly inhibited after this time. Between 72 and 96 h after the beginning of chloroplast development, Sm-treated organisms contain 10 yo of the chlorophyll and 24 of the carotenoids of algae developing in the absence of the antibiotic. The chlorophyll-to-carotenoid ratio in treated organisms at 72 to 96 h is 0.9, the same as is found at 1 2 h for organisms developing in the absence of Sm. In the presence of streptomycin, Euglena never develops the ability to fix CO, photosynthetically, although CO, fixation after I 2 h of development in the absence of the antibiotic can be readily detected. At I 2 h of chloroplast development the following parameters are at comparable levels in Sm-treated and untreated organisms: the bound forms of chlorophyll, concentration of cytochrome 552, the activities of ribulose diphosphate carboxylase, NADP-triose phosphate dehydrogenase, the enzymes converting ribose-yphosphate to ribulose diphosphate, and photosystem I1 activity measured as dye reduction.

No abstract