Multiple amounts of DNA related to the size of chloroplasts : I. An autoradiographic study.
Plants containing genetically small or large plastids appear in some euploid and trisomic types of Beta vulgaris.Small tissue samples of the first 6-10 leaves of nearly 30 euploid plants from 7 different generations were incubated in a solution containing (3)H-thymidine in dark/light cycles, for up to 72 hr. For semiquantitative autoradiography the chloroplasts were then prepared on the slides with various kinds of isolation media, and fixed with OsO4, glutaraldehyde, formaldehyde, or ethanol. The specifity of incorporation was tested by observing the extractability of label after differential treatment with acid or nucleases.Chloroplasts in leaves 2-11 cm long preferentially incorporate (3)H-thymidine. The silver grains over plastids appear to be in clusters (centres). A relationship between the number of grains and also between the number of centres on the one hand, and the chloroplast size on the other could be found.It is concluded that chloroplasts occur in various degrees of polyenergide organization, as has been described, for example, for blue-green algae. Regarding the presence and degree of polyploidy-the other form of genetic "polyvalency" -the experiments provided no information. A remarkable variation in chloroplast size (and number of labelled centres) was observed, not only between different plants or between different leaves of a plants, but also within small tissue samples.
Max-Planck-Institut für Pflanzengenetik, Ladenburg/Rosenhof.
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Herrmann