Light, transmission electron and scanning electron microscopy have been used to investigate the
ultrastructural arrangement of leaf tissue in Triodia irritans, a C4 grass adapted to a hot, dry environment. Photosynthetic tissue was found to constitute 25% of the cross-sectional area of the leaf
and includes mesophyll and bundle sheath cell types. The mesophyll is restricted to discrete areas
and consists of long files of cells interconnected by a complex network of cytoplasm-filled cross
bridges. It is in contact with the vascular tissue via extensions from the bundle sheath, which make
intimate contact with it by way of plasmodesmata located in frequent pit fields. The mesophyll
cytoplasm is largely non-vacuolate, but in other respects is similar to that found in most other
species-viz., contains chloroplasts, mitochondria and occasional microbodies. Cells of the bundle
sheath extensions exhibit a uniform to slightly centripetal distribution of cytoplasm, consisting
mainly of grana-containing chloroplasts, mitochondria possessing elongate cristae, and microbodies.
Cells of the bundle sheath proper, which partially encircles the vascular tissue, do not make direct
contact with the mesophyll and contain fewer chloroplasts than the extension cells.
The arrangement of photosynthetic and of vascular tissues are discussed in terms of the classical
Kranz anatomy that is a feature of C4 plants, and the possible relationships between leaf structure,
photosynthetic activity and the translocation of photosynthate are considered.
Two-Dimensional Electrophoretic Mapping of Proteins of Bundle Sheath and Mesophyll Cells of the C4 Grass Digitaria sanguinalis (L.) Scop. (Crabgrass)
