SUD, RUCHIRA M.* AND NANCY G. DENGLER. Department of Botany, University of Toronto, Toronto, ON M5S 1A1. - Cell lineage of vein formation in variegated leaves of the C4 grass Stenotaphrum secundatum.
Clonal analysis of variegated leaves of the C4 grass, Stenotaphrum
secundatum, indicates that invasions among meristematic layers
occur during the organogenetic stage of leaf development, resulting in
long, broad white and green stripes. These layer invasions cease prior
to the second phase of leaf development when delimitation of leaf
regions occurs. Vein precursors also arise during this second phase,
so that procambial strand formation is superimposed on the lineage
makeup of earlier-formed tissue. Anatomical evidence indicates that
procambium arises through formative divisions within ground tissue of
leaf primordia and that each strand is derived from a variable number
(1-4) of ground meristem precursors. If a developing vein straddles
the boundary between previously-formed green and white sectors, then
the mature vein is half green and half white, reflecting its mixed
cell lineage. In Stenotaphrum, 24.8% of the sectors observed
were bounded by such "half veins". However, analysis of
planes of cell division in developing veins indicates, that once,
formed, procambial strands are discrete lineage units that extend
longitudinally by proliferative division. Thus, lineage restriction
may play an important role in the third stage of leaf developemt,
differentiation of tissues and cells, which also includes the
maintenance of cell identity.
Key words: C4 photosynthesis, cell lineage, clonal analysis, leaf development, Stenotaphrum secundatum, vein formation