LEAFY COTYLEDON MUTANTS OF ARABIDOPSIS

We have previously described a homeotic leafy cotyledon (lec) mutant o f Arabidopsis that exhibits striking defects in embryonic maturation a nd produces viviparous embryos with cotyledons that are partially tran sformed into leaves. In this study, we present further details on the developmental anatomy of mutant embryos, characterize their response t o abscisic acid (ABA) in culture, describe other mutants with related phenotypes, and summarize studies with double mutants. Our results ind icate that immature embryos precociously enter a germination pathway a fter the torpedo stage of development and then acquire characteristics normally restricted to vegetative parts of the plant. In contrast to other viviparous mutants of maize (vp1) and Arabidopsis (abi3) that pr oduce ABA-insensitive embryos, immature lec embryos are sensitive to A BA in culture. ABA is therefore necessary but not sufficient for embry onic maturation in Arabidopsis. Three other mutants that produce trich omes on cotyledons following precocious germination in culture are des cribed. One mutant is allelic to lec1, another is a fusca mutant (fus3 ), and the third defines a new locus (lec2). Mutant embryos differ in morphology, desiccation tolerance, pattern of anthocyanin accumulation , presence of storage materials, size and frequency of trichomes on co tyledons, and timing of precocious germination in culture. The leafy c otyledon phenotype has therefore allowed the identification of an impo rtant network of regulatory genes with overlapping functions during em bryonic maturation in Arabidopsis.