Evidence for variation in the quantity of DNA among plastids of Acetabularia

The DNA content of individual plastids of the giant unicellular algae Acetabularia mediterranea, and Polyphysa cliftoni was studied. Four methods were used for localizing DNA: acridine orange staining, radioautography following actinomycin D-(3)H treatment, electron microscopy of thin tissue sections, and electron microscopy of osomotically disrupted plastids. With each method, DNA was readily detected in 20-35% of plastids, but no DNA was observed in the remaining 65-80%. The results further showed that in those plastids with detectable DNA the amount of DNA present was variable. The sensitivity and reliability of the localization methods are discussed, and the possible implications of these findings are considered.