DIFFERENTIATION OF BUNDLE-SHEATH, MESOPHYLL, AND DISTINCTIVE CELLS INTHE C-4 GRASS ARUNDINELLA-HIRTA (POACEAE)

The C-4 grass Arundinella hirta is characterized by unusual leaf blade anatomy: veins are widely spaced and files of bundle-sheath-like cell s, the distinctive cells, form longitudinal strands that are not assoc iated with vascular tissue. While distinctive cells (DCs) appear to fu nction like bundle sheath cells (BSCs), they differ developmentally in two ways: they are derived from ground meristem rather than procambiu m and they are formed 1-2 plastochrons later. This study describes ult rastructural features of differentiating of BSCs, DCs, and associated mesophyll cells (MCs) during led development BSCs and DCs differ from adjacent MCs by undergoing earlier cell enlargement, greater rates of chloroplast enlargement, reduction of chloroplast thylakoids at late s tages of differentiation, more extensive starch formation, greater wal l thickening, and deposition of a suberin lamella. The precocious deli mitation of the bundle sheath layer is reflected in earlier BSC enlarg ement and vacuole growth. Derivation of DCs from ground meristem is co rrelated with late developmental changes in chloroplast size, wall thi ckness, and plasmodesmatal density. Despite these differences in timin g of events, particularly at early stages, the development of the spec ialized structural features of BSCs and DCs is essentially similar. Th us, proximity to vascular tissue appears to be nonessential for the co ordination and regulation of BSC- and MC-specific developmental events .