Initiation of the Vascular System and the Transition to Flowering in Early Tassels ofZea maysLand Race Chapalote (Poaceae)

Abstract

Serial transections of young tassels of (Zea mays land race) chapalote revealed relationships between the vascular system in its procambial state and the lateral primordia along the axis. A lateral tassel primordium usually consists of an indefinite rim with a prolongation that will become a tassel branch or spikelet pair. A lateral tassel primordium usually develops via modifications of the vegetative leaf primordium in which the leaf apex is enhanced but the leaf base and the bud it produces are suppressed. The clearest sign of the transition from the vegetative state to the tassel is the scale leaf, which is intermediate in form between a vegetative leaf and a lateral tassel primordium. Procambial traces differentiate in isolation in the tassel axis in response to the lateral tassel primordia. Adjacent procambial traces then link axially into sympodia to initiate the three-dimensional vascular system of the tassel axis. Older sympodia occur near the center of the axis interior to more recently initiated procambial traces. Procambial continuity does not occur between the tassel axis and the lateral primordia until isolated traces in the lateral primordia link with the sympodia in the tassel axis. The transition from distichy to polystichy by the lateral tassel primordia occurs as the narrowing of the leaf base makes space available on the tassel axis for lateral primordia out of the vegetative distichous plane.

Phyllotactic pattern is altered in the transition to flowering in the early ears of Zea mays landrace chapalote (Poaceae)

“…This alternation is particularly evident in the transition zone of ear 10 but it is not restricted to the ear. In a study of tassel development in the same landrace we illustrated a similar pattern associated with the transition from vegetative leaf production to reproductive growth in the tassel ( Pizzolato and Sundberg, 1999 ). In that paper, we were more concerned with the shifting and overlapping modifi cations of meristematic activity during leaf and bud development associated with the transition from the vegetative axis into the tassel.…”

“…These critical-point-dried specimens were infi ltrated with Spurr ' s epoxy resin, serially sectioned at 1 or 2 μ m, and stained with 0.05% toluidine blue ( Pizzolato and Sundberg, 1999 ). Camera lucida drawings were made approximately every sixth section using a Leitz (Wetzlar, Germany) Panphot light microscope.…”

“…Recognition of procambial traces in a section, reconstruction of the course of individual procambial traces through serial sections, and estimations of the thickness of the leaf base regions followed the procedures described previously ( Pizzolato and Sundberg, 1999 ). The disk of insertion, as defi ned by Sharman (1942) and used by two of us in an examination of growth primary axis and tassel development ( Pizzolato and Sundberg, 1999, 2001, 2002, is the proximal portion of the leaf base and the adjacent tissues of the axis which expand together if internodal growth occurs. Thickness of the presumptive leaf base regions within the reproductive zones (spikelet pair primordia and spikelet primordia) was estimated by measuring thickness of the lateral primordia from SEM micrographs.…”

“…Thickness of leaf base regions of young tassel primordia of Zea mays landrace Chapalote (modifi ed from Fig. 1 in Pizzolato and Sundberg, 1999 ). Gray rectangles, expanded disk of insertion; B, bud at base of disk of insertion; L, leaf at top of disk of insertion; P, presumptive spikelet pair primordium.…”

“…95 Homogeneity of variance in leaf base thicknesses was tested using the F max test ( Sokal and Rohlf, 1981 ). The terminology and the criteria used to describe the vascular anatomy of the axis and lateral primordia follows Pizzolato and Sundberg (1999, 2001, 2002 except that the term husk leaf denotes the vegetative leaves of lateral ear-forming primary branches.…”