CLASS-II TASSEL SEED MUTATIONS PROVIDE EVIDENCE FOR MULTIPLE TYPES OFINFLORESCENCE MERISTEMS IN MAIZE (POACEAE)

The tassel seed mutations ts4 and Ts6 of maize cause irregular branchi ng in its inflorescences, tassels, and ears, in addition to feminizati on of the tassel due to the failure to abort pistils. A comparison of the development of mutant and wild-type tassels and ears using scannin g electron microscopy reveals that at least four reproductive meristem types can be identified in maize: the inflorescence meristem, the spi kelet pair meristem, the spikelet meristem. and the floret meristem. t s4 and Ts6 mutations affect the fate of specific reproductive meristem s in both tassels and ears. ts4 mutants fail to form spikelet meristem s from spikelet pair meristems. Ts6 mutants are delayed in the convers ion of certain spikelet meristems into floret meristems. Once Borer me ristems are established in both of these mutants, they form Borers tha t appear normal but fail to undergo pistil abortion in the tassel. The abnormal branching associated with each mutant is suppressed at the b ase of ears, permitting the formation of normal, fertile spikelets. Th e classification of the different types of reproductive meristems will be useful in interpretation of gene expression patterns in maize. It also provides a framework for understanding meristem functions that ca n be varied to diversify inflorescence architectures in the Gramineae.