The effect of a heterochronic mutation, Teopod2, on the cell lineage of the maize shoot.

Teopod2 (Tp2) is a semi-dominant mutation of maize that prolongs the expression of characteristics normally confined to the juvenile phase of development. Two of the many dramatic morphological effects of this mutation are an increase in the number of vegetative nodes, and a reduction in the overall size of the shoot. To determine the cellular basis of these phenotypes, the technique of clonal analysis was used to compare the cell division patterns of wild-type and Tp2 plants. Our results indicate that Tp2 increases the number of vegetative nodes produced by the apicalmost cells in the meristem but does not affect the cell lineage of the basal, juvenile, part of the shoot. This result demonstrates that Tp2 does not act uniquely in a 'juvenile' domain of the meristem, but instead causes cells that are normally destined to produce adult structures to express juvenile traits inappropriately. Clonal analysis also demonstrates that Tp2 does not affect the size of the meristem prior to germination, nor does it affect the cell lineage of the basic structural unit of the stem, the phytomer. Thus the effects of this mutation on the size of the shoot are the result of changes in cell fate late in development.