Apparent Identity of Chromoplast and Chloroplast DNA in the Daffodil, Narcissus pseudonarcissus

Although chromoplasts and chloroplasts are mor­ phologically and functionally very different, it has been shown in certain plants and under certain con­ ditions, that they are interconvertible [see 1 5]. One could then expect such plastids to contain, at least qualitatively, the same plastome. It appears questionable, however, whether this applies to all plastid types. For example, FreyWyssling et al. [6] postulated that chromoplasts rep­ resent an irreversible end stage of plastid develop­ ment. This concept, although not universally ap­ plicable, probably describes the situation correctly in some cases, particularly in gerontoplasts [7; see, however, 8]. Further, one could envisage that if the plastome of a given plastid does not represent a single homogenous species, but rather may be, to a limited extent, heterogenous, as suggested by Bedbrook and Bogorad for maize chloroplast DNA [9], then such minor plastome variants in the chloroplast may become selected for and even prevail in the morphologically different chromoplasts. A general comparison of contour length and buoyant density has shown that chloroplast and chromoplast DNA in Tropaeolum majus could be identical [10]. However, a more detailed comparison must be made before this assumption can be veri­ fied. Such comparisons between chloroplast DNAs from different plants have been carried out using