The apicobasal differentiation of the chloroplast population in Acetabularia: In vivo gradient of DNA synthesis

The giant unicellular marine alga Acetabularia, during vegetative growth, may contain up to several million small chloroplasts (Shephard, 1965) which are statistically distributed according to an apicobasal morphological gradient (Hoursiangou, et al 1977). Their biochemical and physiological features also vary along the same gradient: lipid composition (Hoursiangou, et al 1977), photosynthetic capabilities (Issinger, et al 1971), fluorescence properties (Sironval, et al 1973), and protein and RNA syntheses (d’Emilio, et al 1979). Moreover, since cutting off the stalk above the base induces basaltype chloroplasts to give rise to apical-type plastids in the tip of the regenerating nucleate basal fragment, it has been suggested that the cell contains one clone of chloroplasts at various stages of differentiation along the cylindrical alga (Hoursiangou-Neubrun & Puiseux-Dao, 1974).