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Lax midrib1-O, a Systemic, Heterochronic Mutant of Maize

Denise E. Schichnes and Michael Freeling
American Journal of Botany
Vol. 85, No. 4 (Apr., 1998), pp. 481-491
Stable URL: http://www.jstor.org/stable/2446431
Page Count: 11
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Lax midrib1-O, a Systemic, Heterochronic Mutant of Maize
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Abstract

Lxm1-O, a dominant EMS (ethyl methanesulfonate) induced mutation in maize (Zea mays, Poaceae), was originally reported to affect the blade/sheath boundary over the midrib region of the leaf. Here we present a more extensive analysis of the Lxm phenotype in nine different inbred lines. Lxm leaves are longer and narrower, and can initiate ectopic leaves. Additionally, Lxm1-O affects all plant organs observed. Compared to wild-type siblings, Lxm plants have fewer nodes, basal displacement of reproductive structures, and advance more quickly to the reproductive phase. We address questions as to whether Lxm1-O abbreviates a specific developmental phase, using hair, wax, and ear node data. We found that each phase was affected, although to varying degrees, depending on the inbred line. We interpret Lxm1-O to be a heterochronic mutation, causing the developmental acceleration of each phase of the shoot. Lxm1-O is novel, since other systemic heterochronic maize mutants prolong the juvenile phase, thereby extending shoot development. We discuss the importance of heterochronic mutations in the context of morphological evolution.

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