Pit-field distribution, plasmodesmatal frequency, and assimilate flux in the mestome sheath cells of wheat leaves

摘要

The distribution of pit fields and plasmodesmata in the mestome-sheath cells of a wheat leaf has been determined by study of sections and partial macerates. Each bundle is approximately symmetrical about the sagittal plane and most plasmodesmata occur in the mestome sheath where its cells abut the metaphloem. Plasmodesmata are absent adjacent to xylem vessels, and the frequency of plasmodesmata declines sharply in cells that lie close to the sagittal plane. Calculations show that 1 cm2of leaf lamina has approximately 2x108plasmodesmatal connections to the phloem of the longitudinal veins, and that 85 of these connections are to the late-maturing intermediate bundles that do not complete their differentiation until leaf growth is nearly finished. The phloem area of inner tangential wall of the mestome sheath amounts to 0.26 cm2per cm2of leaf area and plasmodesmata occupy 1.5 of this area.