Developmental and Structural Section
Sundberg, Marshall D .
Early pattern formation and evolution of the maize (Zea mays L.) ear.
After more than 100 years of study, the evolution of maize remains unresolved. While molecular, morphological and ontogenetic evidence are in agreement that annual teosinte is the closest relative of maize, few studies have addressed how the two-ranked ear of teosinte evolved into the polystichous ear of maize. Previous studies using SEM elucidated a mechanism of primordium bifurcation that could double the number of ranks once an initial row was established, but they also suggested that earlier changes in the patterning of primordial initiation may also be important. In the present study two developing ears of Zea mays landrace Chapalote, previously examined with SEM, were infiltrated with plastic resin, serially sectioned at 1 or 2 µm thickness, and examined using light microscopy. The patterns of internal procambial differentiation and cell proliferation associated with primordium initiation were traced throughout the length of the ears. The earliest indication of a shift in primordium positioning was a periodic expansion and contraction in the extent of cell proliferation in the "disk of insertion" region of the axis. Primordia were initiated independent of the underlying pattern of procambial development. Procambial differentiation lagged behind the extension of the axis, relative to normal vegetative growth, and was restricted to major axial bundles for 400 µm to more than 1000 µm behind the apex. The 4 major axial bundles formed in the planes defined by the primordial ranks. Proliferation of procambial bundles, which would ultimately supply the developing primordia, was initiated in the region of expanding and contracting disks of insertion. These data suggest that periodic modulation of cell cycles, cell enlargement, or both may be responsible for the shift in primordial patterning by the apical meristem that results in 4 or more ranks in the maize ear compared to 2-ranks in teosinte and other grasses.
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1 - Emporia State University, Biological Sciences, Box 4050, 1200 Commercial Street, Emporia, Kansas, 66801, USA
Presentation Type: Poster
Location: Salon C, D & E - Gov Ballroom/Hilton
Date: Tuesday, August 16th, 2005
Time: 12:30 PM