Clonal sectors reveal that a specific meristematic domain is not utilized in the maize mutant narrow sheath

The narrow leaf and shortened stem phenotypes of the maize mutant narrow sheath (ns) are postulated to result from the lack of founder cell initialization in a region of the meristem that gives rise to leaf and stem margins. To test this model, a lineage map of the maize meristem is presented which compares the development of leaf margins in the narrow leaf mutant, narrow sheath (ns), and wild-type sibling plants. X-irradiation of mature seeds produced aneuploid albino sectors in wild-type and ns mutant plants. Of particular interest are sectors occurring in more than one leaf, which reflect a meristematic albino cell lineage. Analyses of these sectors indicated that: (1) a region of the ns meristem does not contribute to the founder cell population of the incipient leaf; (2) the margins of ns mutant leaves are derived from a lateral region of the meristem different from those in wild-type siblings; (3) founder cells in wild-type, juvenile-staged vegetative meristems encircle the meristem to a greater extent than do founder cells in adult-staged meristems; and (4) meristematic leaf founder cells may be subdivided into specific lateral domains, such that the position of a sector on the meristem correlates with a particular cell lineage. These data support our model for ns gene function in a specific domain of the meristem.