In early work, assumptions of the proportion of M-BS interface area populated by PD varied from 1 to 10% (Osmond, 1971); subsequently, these values and those of Hatch and Osmond (1976), based on median literature values for C3 plant cell PD data, have been routinely used. Pitfields parallel to the cell interface were seen as individual pits while pitfields perpendicular to the cell interface were seen as clusters and were therefore larger. The main drawback of this technique is that TEM sections provide only a thin (200 nm at most) 2D slice of a complex 3D cell wall interface, so the number of PD detected is dependent on the angle at which the pitfield was cut. Nevertheless, when an individual epidermal or cortex-endodermis initial cell in the Arabidopis root meristem is laser-ablated, a neighboring cell belonging to a different lineage divides so that one of its daughters occupies the position of the ablated cell, and differentiates according to its new position rather than its lineage (van den Berg et al., 1995). Vascular strands in tan1 are disorganized and irregularly spaced (compare Fig. In both C3 and C4 species studied, chloroplasts in the M cells were distributed along the cell periphery. Mutations in the C4 grass Panicum maximum that increase leaf interveinal spacing (and hence the maximal distance that an M cell can be from a vein) produce a corresponding increase in C3 photosynthetic characteristics in the leaf (Fladung, 1994). Sites and planes of recent cell division were identified by locating pairs of cells with relatively thin separating walls, in transverse sections. Arrows indicate ME localization in wild-type BS cells (A), tan1 mutant ectopic BS cell clusters (C) and PEPCase localization in wild-type BS cells (B) and tan1 mutant ectopic BS cell clusters (D). bundle sheath cells A layer of cells in plant leaves and stems that forms a sheath surrounding the vascular bundles. In leaves of C4 grasses, the mesophyll cells and bundle-sheath cells typically form two concentric layers around the vascular bundles c. C4 grasses have large bundle-sheath parenchyma cells and have large, conspicuous chloroplasts d. The concentric arrangement of mesophyll and bundle-sheath layers is referred to as Kranz anatomy (wreath) e. al., 2001). conducted all the experiments, imaging, quantification, and data analysis in consultation with S.v.C., R.T.F., R.G.W, and W.P.Q. Each vascular bundle consists of phloem and xylem tissues surrounded by a bundle sheath. The underlying bundle sheath cell surface outside the attachment sites would normally face an intercellular space within the leaf. These observations suggest that veins or their procambial precursors provide a spatial signal for the C4 differentiation of M cells that acts over a limited distance. Alternatively, a procambial cell (BS precursor) and a ground cell (M precursor) may have been derived from a division at the site of the sectoring event. This demonstrates that the ectopic BS cells in tan1 leaves are more closely related to normally positioned BS cells than they are to the M cells with which they share a vein-distal location. These two factors combined resulted in C4 species having higher PD density per cell interface area compared with C3 species, consistent with the findings of Botha (1992). and R.T.F. 5C,D). 1D compared with 1C). Regions of contact between M cells and BS cells that could be visualized with scanning electron microscopy (Figure 3) were exposed by tearing critical point dried leaf tissue parallel to the veins. They remain surrounded by parenchymatous bundle sheaths. For the C3 species, rice and wheat, sucrose flux per PD was obtained by dividing CO2 assimilation rate per PD by 12. This has severely limited our ability to model C4 photosynthetic flux and strategies for determining the genetics and evolution of the anatomical specialization for C4 metabolite flux. C3 species also had larger pitfield areas on both the M-BS and M-M cell interfaces compared with the C4 species examined (Figure 5). Acta, Plasmodesmata of maize root tips: structure and composition, Biochemical Models of Leaf Photosynthesis, Elements required for an efficient NADP-malic enzyme type C, SAUR17 and SAUR50 Differentially Regulate PP2C-D1 during Apical Hook Development and Cotyledon Opening in Arabidopsis, AUTOPHAGY-RELATED14 and Its Associated Phosphatidylinositol 3-Kinase Complex Promote Autophagy in Arabidopsis, by The American Society of Plant Biologists, The Metabolite Pathway between Bundle Sheath and Mesophyll: Quantification of Plasmodesmata in Leaves of C3 and C4 Monocots. Light Micrographs of Transverse Sections of Leaves of the Two C3 Species and Two C4 Species Examined. Using a Mutator transposable element as a molecular probe, we identified a tightly linked restriction fragment length polymorphism that cosegregated with the bsd2 -conferred phenotype. Were calculated using the equation described by Pengelly et al sides of highly lobed mesophyll cells final... 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