Development of microtubules in chloroplasts of two halophytes forced to follow Crassulacean acid metabolism

Immunocytological and chemical studies on the stromacentre-forming protein from Avena plastids

The stromacentre (SC), a particular structure in the plastids of Avena, was isolated from etioplasts of Avena sativa by density gradient centrifugation and then analyzed and compared with ribulose-1,5-bisphosphate carboxylase-oxygenase (RuBPCase) from A. sativa, with pyrenoids of Chlorella vulgaris and with the "stromacentre" of Opuntia. Purified SC-elements consisted of protein subunits with a relative molecular weight of 63 kDa, different from the isolated RuBPCase of A. sativa as shown by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. After peptide mapping, the proteolytic cleavage patterns of the 63-kDa protein were also found to be different from those of the RuBPCase. Antibodies against SC-elements, RuBPCase, and the large subunit of RuBPCase were produced. Ouchterlony double immunodiffusion tests did not give crossreactions between the SC-elements and RuBPCase or the large subunit of this enzyme. Immunogold labelling of ultrathin sections showed that antibodies against the SC-elements marked the stromacentre in Avena, but not the pyrenoids in Chlorella. Antibodies against the large subunit of RuBPCase, however, did not label the SC, but labelled the stroma of the plastids in Avena and the pyrenoids of Chlorella. In Opuntia, a comparable structure described as an SC was not labelled by any of the antisera. Immunoelectrophoretical investigations demonstrated a strong correlation between the presence of the 63-kDa protein and the occurrence of the SC in different Avena species with and without SC.

Morphological and chemical studies on the crystalloid-forming 'succulent protein' from normal and ribosome-deficient Aeonium domesticum plastids

Aeonium domesticum cv. variegatum is a mesochimera of the constitution green/white/green with normal proplastids and chloroplasts in the unaffected tissues and ribosome-deficient colourless mutant plastids in the white leaf tissues. All the different plastid types contain 'succulent protein crystalloids' (SPC). For more detailed characterization, the SPC elements were freed from the plastids and purified by gel filtration. Electron microscopy of different fractions revealed five levels of structural organization. Beginning with the most complex state, the levels are designated as 'succulent protein (SP) organizational state' V (hexagonally arranged and closely packed tubules in the stroma of intact plastids) to I (globular protomers of 5 nm diameter as the basic structure of SPCs). Highly purified SP-fractions were shown by means of sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) to consist of two or three proteins of Mr 56 kdalton, 58 kdalton and 60 kdalton, depending on the buffer medium used for SP isolation and the duration of storage of leaves in the frozen state. In the urea/SDS-PAGE system, these proteins show similar mobilities to α- and β-tubulin, but no immunoreaction against antitubulin. The proteolytic cleavage pattern of tubulin subunits and SP proteins are different. Their locations on two-dimensional isoelectric focusing-SDS gels show some overlappings because of microheterogeneities in both proteins in the pH gradient from pH 4.5 to 6.5. Malatedehydrogenase activity could not be detected in the purified SP fractions.

Protein crystalloids in ribosome-deficient plastids of Aeonium domesticum cv. variegatum (Crassulaceae)

Protein crystalloids are typical constituents of Aeonium domesticum plastids. They are composed of hexagonally arranged tube-like elements situated in the stroma without a bordering membrane. The single tubule has an external diameter of about 20 nm and an internal one of about 10 nm. The green-white-green mesochimera Ae. domesticum cv. variegatum contains normal chloroplasts in the green tissue and colourless plastids in the pale tissue. The defective plastids have a double-layered envelope, scarce internal membrane structures and contain, in the mature stage, a large vacuole. Plastid ribosomes can be detected only rarely in proplastids. They lose their ribosome complement entirely in the course of development. Polyacrylamide gel electrophoresis of total nucleic acids extracted from white tissue revealed the absence of the 23S and 16S rRNA normally present in plastids. Despite the loss of ribosomes, the plastids contain large protein crystalloids, which are structurally identical with those of normal green chloroplasts. Consequences concerning problems of encoding and transport of crystalloid protein(s) are briefly discussed.