Normal 0 21 false false false MicrosoftInternetExplorer4 On the taxonomic position of Panicum scabridum (Poaceae, Panicoideae, Paspaleae) /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Tabla normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-parent:""; mso-padding-alt:0cm 5.4pt 0cm 5.4pt; mso-para-margin:0cm; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:10.0pt; font-family:"Times New Roman"; mso-ansi-language:#0400; mso-fareast-language:#0400; mso-bidi-language:#0400;}

Panicum scabridum, an incertae sedis species of Panicum s.l., is here included in the genus Coleataenia, following a phylogenetic analysis based on one new ndhF sequence of the species and associated morphological data. Panicum scabridum and species of Coleataenia are cespitose and perennial plants, with a lower glume (1–)3–5-nerved, 1/3 to 3/4 of the spikelet, upper glume and lower lemma 5–9-nerved, and upper anthecium smooth, shiny, and indurate. Within Coleataenia, P. scabridum appeared as the sister taxon of the species pair C. prionitis and C. petersonii; these three species are the only NADP-me taxa of tribe Paspaleae exhibiting two bundle sheaths around the vascular bundles, i.e., with an outer parenchymatous sheath and an inner mestome sheath with specialized chloroplasts. The new combination Coleataenia scabrida is proposed and a lectotype is designated.

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.

Infrageneric phenetic relations in new world Panicum (Poaceae: Panicoideae: Paniceae): a numerical analysis

Numerical studies based on 64 characters placed 188 American species of the genus Panicum L. in 23 sections clustered in five major groups. The same major groups were obtained when the five characters that define the subgenera were excluded from the analyses. Groups 1 and 2 included C4 species. Species with an outer parenchymatous sheath in group 1 corresponded to subg. Panicum, whereas species with a single mestome sheath in group 2 corresponded to subg. Agrostoides. Group 3 included the intermediate C3–C4 species belonging to subg. Steinchisma. C3 sections were clustered together but arranged in a different way than previous classifications. Group 4 included sections from subg. Phanopyrum with basic chromosome number x = 10, whereas group 5 included the other sections of Phanopyrum with x = 9 together with sections from subg. Dichanthelium also with x = 9. The two subgroups of subg. Phanopyrum are not only different in chromosome number but also in inflorescence type and upper anthecium ornamentation. On the other hand the x = 9 sections of Phanopyrum remain in the same cluster with sections from subg. Dichanthelium in numerical analyses where basic chromosome number is removed. These results suggest the possibility of sinking Dichanthelium into Phanopyrum and then split the latter when more cytological data become available. Kranz syndrome and basic chromosome number were the characters with the highest contribution to the delimitation of the major groups. On the basis of these results different existing hypotheses on the classification of the genus Panicum are discussed. Key words: Panicum, numerical taxonomy.

Kranz distinctive cells in the culm of ArundineUa (Arundinelleae; Panicoideae; Poaceae)

The transectional anatomy of photosynthetic flowering culms of Arundinella berteroniana (Schult.) Hitchc. Chase and A. hispida (Willd.) Kuntze from South America and A. nepalensis Trin. from Africa is described and illustrated. The vascular bundles are arranged in three distinct rings, the outermost being external to a continuous sclerenchymatous band. Each of these peripheral bundles is surrounded by two bundle sheaths, a complete mestome sheath and an incomplete, outer, parenchymatous Kranz sheath, the cells of which contain large, specialized chloroplasts. Kranz bundle sheath extensions are also present. The chlorenchyma tissue is also located in this narrow peripheral zone and is interrupted by the vascular bundles and their associated sclerenchyma. Dispersed throughout the chlorenchyma are small groups of Kranz distinctive cells, identical in structure to the outer bundle sheath cells. No chlorenchyma cell is. therefore, more than two cells distant from a Kranz cell. The structure of the chlorenchyma and bundle sheaths indicates that the C4 photosynthetic pathway is operative in these culms. This study clearly demonstrates the presence of the peculiar distinctive cells in the culms as well as in the leaves of Arundinella. Also of interest is the presence of an inner bundle sheath in the vascular bundles of the culm whereas the bundles of the leaves possess only a single sheath. It has already been shown that Arundinella is a NADP-me C4 type and the anatomical predictor of a single Kranz sheath for NADP-me species, therefore, either does not hold in the culms of this genus or the culms are not NADP-me. This is only the second reported breakdown of this association between MS anatomy and the NADP-me biochemical C4 type.

Water Pathways in Wheat Leaves. IV. The Interpretation of Images of a Fluorescent Apoplastic Tracer

Sections of wheat leaves fed with the fluorescent apoplastic tracer sulforhodamine G (SR) through the xylem were prepared by freeze-substitution and resin embedding. The distribution of fluorescence intensity (FI) of the tracer was measured by microspectrofluorometry at a resolution of 0.4 �m. SR was found to move within cell walls in restricted paths less than 200 nm wide. The name 'nanopaths' is suggested for these. The highest FI was found around the mestome-sheath / parenchyma-sheath border on the xylem side, and was shown to be due, not to binding of the tracer to wall components, but to the generation of a very high concentration of SR there by the separation of water from the solute. This separation cannot be evaporative but must be osmotic, and is presented as evidence of a major symplastic water movement starting at the parenchyma sheath cell membrane. The main resistance to water loss from the veins is at the mestome sheath and appears to be controlled by the suberised lamellae.