The stromacentre of plastids of Kalanchoë pinnata Persoon

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.

TANSLEY REVIEW No 1.: VARIATION IN PHOTOSYNTHETIC ACID METABOLISM IN VASCULAR PLANTS: CAM AND RELATED PHENOMENA

The term, photosynthetic acid metabolism (PAM), encompasses processes which involve four-carbon (C₄ ) acids as carbon-carrying intermediates between the carboxylations catalysed by phosphoenolpyruvate (PEP) carboxylase and ribulose biphosphate (RuBP) carboxylase. These carboxylations may be separated either spatially, as in C₄ photosynthesis which is not covered here, or temporally. Separation in time is referred to as diel PAM (DPAM) and the variations on this particular theme are the subject of this review. DPAM includes stomatal and astomatal types. The former types, usually described as crassulacean acid metabolism (CAM), are referred to here as stomatal CAM (SCAM). Astomatal PAM includes both aquatic and terrestrial forms; aquatic acid metabolism (AAM) and terrestrial astomatal acid metabolism (TAAM). Physiological, biochemical, structural, ecological and evolutionary aspects of these mechanisms of acquisition of carbon dioxide are reviewed. CONTENTS Summary 3 I. General Introduction to Photosynthetic Acid Metabolism (PAM) 4 II. Stomatal Crassulacean (Diel Photosynthetic) Acid Metabolism (SCAM) 5 III. Astomatal Photosynthetic Acid Metabolism 13 IV. Idling 18 V. Structural Variation in Plants Exhibiting Diel PAM (DPAM) 18 VI. The Mechanism of the Switch between C₃ Photosynthesis and DPAM 19 VII. The Cost of DPAM 19 VIII. The Evolution of DPAM 20 IX. Concluding Comment 22 Acknowledgements 22 References 22.

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.

PLASTID INCLUSIONS IN EPIDERMAL CELLS OF BETA

Inclusions were found in epidermal plastids of Beta vulgaris L., by the use of the electron microscope. One type of inclusion resembles the membrane-bound plastid inclusions found by others in various meristematic plant cells; the other does not appear to have been described before. The second type of inclusion is not membrane-bound and appears elongated and fibrillar in longisection. The elongated plastid inclusion sometimes becomes quite large. It is postulated that Beta epidermal cells may store two different proteins under some conditions.

Microbodies and an anomalous "microcylinder" in the ultrastructure of plants with Crassulacean acid metabolism

An ultrastructural study was made of the leaf tissues of four species of plants in three genera with Crassulacean acid metabolism ("CAM" plants): Kalanchoë daigremontiana Hamet et Perrier, K. verticillata Elliot, Sedum rubrotinctum clausen and Crassula tetragona L. Microbodies similar in appearance, with fibrillar or granular nucleoids but no crystalline deposits, were present in the mesophyll of all four species. The microbodies resembled in size and abundance those of C3 plants more closely than those of C4 plants, both under long-day and short-day conditions. The reaction for catalase activity employing 3,3'-diaminobenzidine produced a heavy deposit in the microbodies; the reaction was blocked by the catalase inhibitor, aminotriazole.Some of the plants of the two species of Kalanchoë studied contain in the epidermal and mesophyll cells of the leaves and plantlets an organelle-like structure consisting of a hollow cylinder, 90-160 nm in diameter and up to 2 μm or more in length, around which 18-20 or more minute tubules are wound in a steep helix. The tubules are only ca. 9 nm in diameter, hence are much smaller than conventional microtubules. The cylinder and surrounding tubules, herein tentatively assigned the term "microcylinder" for convenience, may represent a product of viral infection, or may be an organelle that appears at certain stages of growth or under particular environmental conditions. In any case it may prove to be of considerable importance for investigators of CAM plant physiology.