[The effect of inhibitors of RNA- and protein synthesis on the chlorophyll content of nucleate and anucleate cells of Acetabularia].

The chlorophyll content in anucleate cells of the green alga Acetabularia mediterranea increases during about four weeks after enucleation. This corresponds exactly to the peroid of total protein synthesis and synthesis of the enzyme UDPG-pyrophosphorylase, which is coded by nuclear DNA. When nucleate posterior pieces of the stalk are treated with actinomycin (10 μg/ml), the increase in chlorophyll content is blocked completely after a lag period. Morphogenesis and synthesis of the UDPG-pyrophosphorylase are strongly inhibited also. As is well known, anucleate cells of Acetabularia contain a storage of long lived nucleus dependent messenger-RNA within the tip region of the stalk. Therefore actinomycin has only a little influence on stalk and cap formation and no influence on the synthesis of the UDPG-pyrophosphorylase in anucleate cells. On the other hand the antibiotic strongly inhibits the increase in chlorophyll content in such pieces.Chloramphenicol (100 μg/ml) completely blocks the increase in chlorophyll content in both nucleate and anucleate cells but inhibits the synthesis of the UDPG-pyrophosphorylase only slightly in the beginning. Inhibition which sets in later is very likely a secondary effect. Actidion (0.25 μg/ml) and puromycin (30 μg/ml) strongly inhibit the increase in chlorophyll content and UDPG-pyrophosphorylase synthesis in both nucleate and anucleate cells. This inhibition is partly reversible. It is concluded from these results that the chlorophyll content of the cells is controlled not only by nuclear genes but also by the DNA of the plastids and that protein synthesis is necessary for chlorophyll formation or stabilization.Some possibilities of how chloroplast DNA may control chlorophyll formation and stability are discussed.