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In contrast,
plants that overexpress floral MADS factors, such as AP1, AG, or AP3 with PISTILLATA, typically have a shorter vegetative
phase than do wild-type plants, resulting in fewer rosette leaves and earlier flowering (reviewed in Ma 1998). Given the accumulation pattern of AGL15 in wild-type plants, AGL15 might act by prolonging or promoting the early juvenile
phase in the transgenic plants; that is, it may "juvenilize" the plants. Effects at the beginning of the juvenile phase would
translate into a delay in flowering because competence to flower is acquired in an age-dependent fashion (Thomas 1993). A partially juvenilized plant might require a longer period or stronger inductive signals before flowering.
The petioles of the cotyledons and rosette leaves were considerably shorter and the leaf blades were shorter and rounder in
plants carrying AGL15 transgenes. In wild-type Arabidopsis, rounded leaves are produced during the earliest stages of vegetative growth, whereas
increasingly spatulate leaves are produced later (Bowman 1994 ; Poethig 1997). Although the change in leaf shape suggests a more juvenile mode of morphogenesis in the transgenic plants, leaf shape is
too variable and the regulation of leaf shape is too complex (reviewed in Poethig 1997) for this character to serve as a definitive marker of phase. In Arabidopsis, a more consistent marker of the juvenile phase
is the absence of trichomes on the abaxial surface of the leaf (Telfer et al. 1997).
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