Analysis of DNA of male and femaleSphaerocarpos donnellii Aust. (Liverwort)

Plastid gene expression in a yellow-green leaf mutant of Petunia hybrida

We have analyzed the morphology and gene expression in plastids of a yellow-green leaf mutant of Petunia hybrida (E 5059). Under normal light intensities (20,000 lx), yellow-green leaves develop with a typical proplastid morphology (few membranes, incomplete stacking). When such plants are grown under low light intensities (3,000 lx), the newly formed leaves are green. The plastids in these green leaves have a wild-type like chloroplast morphology (thylakoids and grana structure). Pre-existing green leaves remain green in 20,000 lx, indicating that chlorophyll is not degraded. An analysis of polypeptides synthesized in isolated plastids from the yellow-green and green leaves of this mutant plant shows several differences. In the yellow-green leaf plastids only a very small amount of the large subunit of ribulose-1,5-bisphosphate carboxylase (RuBPCase) is present, while in green plastids this polypeptide is present in much higher amounts. Hybridization experiments indicated that in plastids from the yellow-green leaves the mRNA coding for the large subunit polypeptide is present in much lower amounts than in plastids from the 3,000 lx green leaves of this mutant or in chloroplasts from wild type plants. These results indicate regulation at the mRNA level. Furthermore, in yellow-green leaf plastids eleven polypeptides are present with high molecular wieght (higher than 67,000 d). Five of them are synthesized by the yellow-green leaf plastid itself. Such high molecular weight polypeptides are also synthesized by proplastids isolated from white petunia cell suspension cultures, but are not synthesized by 3,000 lx green leaf plastids, or by isolated normal leaf chloroplasts. These results indicate that the synthesis of these polypeptides is specific for the proplastid stage of chloroplast biogenesis.

Chloroplast DNA from three archegoniates

1. DNA from female and male Sphaerocarpos donnellii (liverwort) plants exhibits at least two species with buoyant densities of 1.703 (main band) and 1.691 (satellite) g cm(-3) in CsCl equilibrium gradients. At least part, if not all, of the satellite DNA is localized in plastids. It consists of up to 90% of uniformly sized circular molecules of an average circumference of 38.5 μm. Compared to other Chlorophyta, the liverwort's cpDNA is unusually low both in diensity and contour length. - 2. On the hand, cpDNA from the ferns Asplenium nidus and Pteris vittata resembles those of higher plants in buoyant density (1.697 g cm(-3)) and circumference (about 44.8 μm). - 3. Analysis of DNA from the archegoniate chloroplasts with restriction endonucleases indicates chat the cyclic molecules are monomers. - 4. The results show that the circular molecules found in cpDNA of higher plants do not represent the functionally required minimum size of DNA in plastids.