MORPHOGENESIS IN PINOID MUTANTS OF ARABIDOPSIS-THALIANA

A series of mutants of Arabidopsis thaliana was selected in which the inflorescence stem elongates but loses the ability to produce flower p rimordia on its flanks. Mutants fell into two classes, further occurre nces of pin-formed mutants and mutations at a new locus named pinoid. As well as causing inflorescence defects, pinoid mutations result in p leiotropic defects in the development of floral organs, cotyledons and leaves. Most changes involve the number of organs produced rather tha n their differentiation suggesting that PINOID controls an early gener al step in meristem development. pinoid mutant defects are similar to those seen in pin-formed mutants for inflorescences and flowers, but d ifferent for cotyledons and leaves indicating that the two genes have separate but overlapping functions. A defect in polar auxin transport is implicated in the pin-formed mutant phenotype, but in young inflore scence stems of even the strongest pinoid mutants it occurs at close t o wild-type levels. It is markedly reduced only after stems have cease d elongating. Thus, it is likely that polar auxin transport is seconda rily affected in pinoid mutants rather than being directly controlled by the PINOID gene product. Even so, double mutant studies indicate th at the process controlled by PINOID overlaps with that specified by th e AUXIN RESISTANT1 gene, suggesting that PINOID plays some role in an auxin-related process.