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Journal of Cell Science, Vol 11, 357-377, Copyright © 1972 by Company of Biologists

Submitted on December 6, 1972

Variable Amounts of Dna Related to the size of Chloroplasts

IV. Three-Dimensional Arrangement of Dna in Fully Differentiated Chloroplasts of Beta Vulgaris L.

K. V. KOWALLIK 1 and R. G. HERRMANN 1

1 Botanisches Institut der Universität, 355 Marburg/Lahn, Pilgrimstein 4, Germany Max-Planck-Institut für Pflanzengenetik, 6802 Ladenburg/Neckar, Rosenhof, Germany

All correspondence to R. G. Herrmann

Glutaraldehyde-fixed strips of fully differentiated leaves of Beta vulgaris L. were treated with proteases. With this method it is possible to display DNA-regions in chloroplasts selectively and to reconstruct them from serial sections.

As in young plastids, the DNA in mature plastids is also distributed within several regions which are separated rather clearly by thylakoids. The number of such regions depends upon the size of the organelle and thus upon its developmental state. The shape of the regions is, in contrast to less-differentiated plastids, mostly elongated. The individual regions seem to contain unequal quantities of DNA-fibrils.

A comparison of our ultrastructural results and biochemical data (DNA-amounts per plastid depending on the size of the organelle; kinetic complexity of chloroplast-DNA of Beta) as well as a comparison of the chloroplast with similar prokaryotic systems (as in bacteria, blue-green algae, and mitochondria) leads to the suggestion that each DNA-containing region can be regarded as a single nucleoid. In addition, each nucleoid already contains several (on average, 4-8) genetic units. Thus the chloroplast of Beta seems genetically polyvalent in at least 2 respects: (i) it is of polyenergidic organization, and (ii) the individual nucleoids can be polyploid to varying degrees.

Submitted on December 6, 1972




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© The Company of Biologists Ltd 1972