Developmental and Structural Section
Sundberg, Marshall .
The roles of shank and husk leaves in the origin of the maize ear.
Most investigations of the evolution of the maize ear have ignored the possible roles of the shank and husk leaves even though the ear terminates this reproductive branch. The ear branch originates as an "axillary" bud opposite the midrib of its associated leaf, just below the overlap of the ensheathing marginal meristems. Because of the constraint of the midrib area of the next lower leaf, the shape of the bud meristem is initially flattened and resembles the appearance of a spikelet pair primordium in the tassel or ear prior to bifurcation. In quick succession two primordium initials are formed on the opposite lateral sides of the bud meristem. Although these tips remain separate as the primordia enlarge, their bases join on the axial side and they grow as a compound structure, the two-keeled prophyll. Successive husk leaves are initiated in an originally decussate pattern established by the two prophyll initials. This pattern is identical to the leaves on the main culm with the ensheathing husk leaf bases overlapping on alternate sides. In several land races, and the cultivar B73, one to three secondary ear branch meristems are occasionally initiated in association with one side of the prophyll and/or the next older one or two husk leaves. In a few instances a third order ear branch meristem forms in association with the prophyll or first husk leaf of the second order branch ear. Small ears terminate these higher order branches, a situation resembling multiple-branching ear shoots in teosinte. Beginning at about the 5th husk leaf, the phyllotaxy begins to shift to a spiral pattern which is continued into the spikelet pairs at the base of the ear. Early ear shoot development in maize is more similar to that of teosinte than was previously thought.
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1 - Emporia State University, Department Of Biological Sciences, 1200 COMMERCIAL, EMPORIA, KS, 66801, USA
Presentation Type: Oral Paper:Papers for Sections
Location: Union D/Hyatt
Date: Tuesday, July 10th, 2012
Time: 5:00 PM