Photosynthetic Pathway-Related Ultrastructure of C3, C4 and C3-Like C3-C4 Intermediate Sedges (Cyperaceae), With Special Reference to Eleocharis

The ultrastructure of photosynthetic organs (leaf blades and culms) was investigated in eight species from four genera of sedges: Fimbristylis (C, fimbristyloid anatomy), Pycreus (C4 chlorocyperoid anatomy), Rhynchospora (C4 rhynchosporoid anatomy) - all NADP-ME (malic enzyme) type, and uninvestigated C3, C4 (eleocharoid anatomy, NAD-ME type) and C3-like C3-C4 intermediate species of Eleocharis. Ultrastructural characteristics previously reported for the former anatomical types are largely confirmed, though some evidence of poorly developed peripheral reticulum in C4 rhynchosporoid sedges is presented. Sedges, regardless of anatomical and biochemical type, possess a suberised lamella in photosynthetic organs which is invariably present in and confined to the mestome sheath cell walls, though it is often incomplete in the radial walls. By contrast with other C4 sedges, NAD-ME Eleocharis species and the C3-like C3-C4 intermediate E. pusilla possess abundant mitochondria and chloroplasts with well-stacked grana in the photosynthetic carbon reduction (PCR) (Kranz)/bundle sheath cells. Peripheral reticulum is well developed in NAD-ME species in both PCR and photosynthetic carbon assimilation (PCA) (C4 mesophyll) chloroplasts, but differs from that seen in chlorocyperoid and fimbristyloid type sedges. The suberised lamella and starch grains (well preserved), and granal stacks (poorly preserved) are identifiable in dried herbarium material (Eleocharis). Prediction of C4 biochemical type of sedges should be possible by combining anatomical, ultrastructural and δ13C value data. The significance of the ultrastructural similarities between the C4 NAD-ME and C3-C4 intermediate Eleocharis species is discussed.

Bundle sheath and mesophyll cell differentiation in the C4 dicotyledon Atriplex rosea: quantitative ultrastructure

In leaves of most C4 species, both bundle sheath and mesophyll cells are derived from ground meristem, yet at maturity differ in photosynthetic enzyme complement and in cell size, shape, and subcellular ultrastructure. This quantitative ultrastructural study of bundle sheath and mesophyll cell differentiation in Atriplex rosea shows that while developmental pathways of bundle sheath and meosphyll cells are generally coordinated, the timing of developmental divergence differs among individual characteristics. For instance, bundle sheath cells are larger, with more chloroplasts and more and larger mitochondria by 8 days after leaf emergence, while differential growth of mesophyll cell chloroplast peripheral reticulum and increase in thylakoids per granum in bundle sheath chloroplasts do not develop until after 12 days. Multigroup principal components analysis (M-PCA) of the data emphasizes that the greatest source of variation is overall size change as both cell types expand. M-PCA also identifies patterns of allometry within the data; for instance, mesophyll cell vacuoles and chloroplast peripheral reticulum undergo greater relative growth than do bundle sheath microbody area and number. The greater structural specialization of bundle sheath cells is reflected in higher growth rates from the time of divergence, but developmental change in both cell types continues until leaf expansion is complete. Most structural changes occur substantially after the stage of cell-specific expression of C4 enzymes. Key words: bundle sheath, mesophyll, C4 photosynthesis, leaf development, Atriplex rosea, multigroup principal components analysis.

Structural aspects of the leaves of seven species of Portulaca growing in Hawaii

Seven species of Portulaca growing in Hawaii can be divided into two groups based on the morphology, anatomy, and ultrastructure of their leaves. Portulaca oleracea, P. molokiniensis, P. lutea, forming group A, have spatulate to obovate leaves, paradermal minor veins, and mesophyll cells that completely encircle the minor veins. The chloroplasts in their bundle sheath cells are larger than those in the mesophyll cells and have well-developed grana and reduced peripheral reticulum. Bundle sheath mitochondria are larger and more numerous than those in the mesophyll, and chloroplasts in the mesophyll cells have well-developed grana and peripheral reticulum. Portulaca pilosa, P. villosa, P. sclerocarpa, and P. "ulupalakua," forming group B, have lanceolate to oblong–oblanceolate leaves, peripheral minor veins, and incomplete wreaths of mesophyll cells. The choroplasts in their bundle sheath cells are about the same size as those in the mesophyll and have reduced grana and well-developed peripheral reticulum. The bundle sheath mitochondria are about the same in size and number as those in the mesophyll, and the mesophyll chloroplasts have well-developed grana and reduced peripheral reticulum. Groups A and B may be equivalent, respectively, to types ii and i of R. C. Carolin, S. W. L. Jacobs, and M. Vesk (Aust. J. Bot. 26: 683–698, 1978) and to coronary subtypes B and A of E. V. Voznesenskaya and Y. V. Gamalei (Bot. Zh. Leningrad, 71: 1291–1306, 1986), which constitute groupings of Portulaca species studied by those authors.

Étude comparée de l'ultrastructure des stomates ouverts et fermés chez le Tradescantia virginiana

Guard cells and subsidiary cells of Tradescantia virginiana L. were examined with transmission and scanning electron microscopy. No plasmodesmata occur in the walls between the guard cells and the subsidiary cells. The numerous mitochondria suggest that guard cells are very active. Numerous small vacuoles were observed in closed stomata, whereas few and large vacuoles were present in opened stomata. A specialized peripheral reticulum and some invaginations containing cytoplasm were observed in chloroplasts of opened stomata. This increase of effective surface of the membrane presumably allows a rapid exchange of substances to or from the chloroplast. This was not observed in mesophyll plastids. The structures described are discussed in relation to guard cell physiology.

Mitochondria and Chloroplast Peripheral Reticulum in the C4 Plants Amaranthus edulis and Atriplex spongiosa

Cytochemical techniques were used to show that all the many large mitochondrion-like bodies present in bundle sheath cells of the aspartate-donor C4 plants, Amaranthus edulis and Atriplex spongiosa, possessed mitochondrial characteristics. The techniques involved the location of cytochrome c oxidase activity with 3,3'-diaminobenzidine and examination of configurational changes in mitochondria after incubation in the inhibitors of oxidative phosphorylation, rotenone and oligomycin, and of substrate phosphorylation, iodoacetate, or the uncouplers of oxidative phosphorylation 2,4-dinitrophenol and carbonyl cyanide p-trifluoromethoxyphenylhydrazone. The peripheral reticulum, which is a prominent feature of C4 mesophyll and bundle sheath chloroplasts and whose internal structure closely resembles that of the bundle sheath mitochondria, was also examined cytochemically. Frequent protrusions or buds from the peripheral reticulum in the bundle sheath chloroplasts strongly suggested that it could give rise to all or some of the mitochondria. Cytochemical investigation with diaminobenzidine, however, demonstrated that the peripheral reticulum does not possess cytochrome c oxidase activity and that the mitochondrial population is homogeneous. Studies of developing leaves of Amaranthus edulis showed that the mitochondria were a prominent feature in the bundle sheath cells before the appearance of the peripheral reticulum. The close proximity of the peripheral reticulum to mitochondria or to peroxisomes and sometimes also to the cell wall plasmodesmata indicates that it may play a role in metabolite transport.