Cell Lineage of Vein Formation in Variegated Leaves of the C4Grass Stenotaphrum secundatum

Clonal analysis of variegated leaves of the C₄grass, Stenotaphrumsecundatum, indicates that invasions among meristematic layersoccur during the organogenetic stage of leaf development, resultingin long, broad white and green stripes. These layer invasionscease prior to the second phase of leaf development when delimitationof leaf regions occurs. Vein precursors mostly arise duringthe second phase, so that procambial strand formation is superimposedon the lineage makeup of earlier-formed tissue. Anatomical evidenceindicates that procambium arises through formative divisionswithin ground tissue of leaf primordia and that each strandis derived from a variable number (one–four) of groundmeristem precursors. If a developing vein straddles the boundarybetween previously-formed green and white sectors, then themature vein is half green and half white, reflecting its mixedcell lineage. In Stenotaphrum, 24.8% of the sectors observedwere bounded by such ‘half veins’. The temporalrelationship of layer invasion and tissue system delimitationin this species supports the view that positional signals aremore important than lineage history in the determination oftissue type. However, analysis of planes of cell division indeveloping veins indicates, that, once formed, procambial strandsare discrete lineage units that extend longitudinally by proliferativedivisions. Thus, lineage restrictions may play an importantrole in the third stage of leaf development, differentiationof tissues and cells, which also includes the maintenance ofcell identity.Copyright 2000 Annals of Botany Company C₄photosynthesis, cell lineage, clonal analysis, leaf development, St. Augustine’s grass,Stenotaphrum secundatum , variegation, vein formation