THE ULTRASTRUCTURE AND COMPUTER-ENHANCED DIGITAL IMAGE-ANALYSIS OF PLASMODESMATA AT THE KRANZ MESOPHYLL-BUNDLE SHEATH INTERFACE OF THEMEDA-TRIANDRA VAR IMBERBIS (RETZ) CAMUS,A. IN CONVENTIONALLY-FIXED LEAF BLADES

The ultrastructure of the plasmodesmata at the Kranz mesophyll-bundle sheath (KMS-BS) interface in Themeda triandra, and the substructures within the plasmodesmata were investigated, using conventionally fixed leaf-blade material, enhanced by the addition of OT % tannic acid to the primary fixative. Examination of high-resolution electronmicrographs, and computer-enhanced digital images suggests that these plasmodesmata are complex structures, comprised of helically-arranged particulate material. The electron-dense particles are between 2-5 and 3'0 nm in diameter. These particles are specifically associated with the inner face of the inner plasmalemma membrane leaflet, and the outer region of the desmotubule wall. The electron-dense particles are presumably proteinaceous and embedded in a lipid matrix. In the constricted median portion of the KMS-BS plasmodesmata, the space between the desmotubule and the inner plasmalemma membrane leaflet and areas surrounding the proteinaceous particles thereof (the cytoplasmic sleeve) is about 3 nm in cross-section, and constitutes what we believe to be the space through which intercellular transport takes place. © 1993 Annals of Botany Company.