Early inflorescence and floral development in Zea mays land race Chapalote (Poaceae)

Abstract

Tassel and ear primordia were collected from greenhouse‐grown specimens of the Mexican maize landrace Chapalote and prepared for scanning electron microscopic (SEM) examination. Measurements of inflorescence apices and spikelet pair primordia (spp) were made from SEM micrographs. Correlation of inflorescence apex diameter with number of spikelet ranks showed no significant difference between tassels and ears, except at the two‐rank level where the ear apical meristem had a significantly smaller diameter than corresponding two‐ranked tassels. Within individual inflorescences, spp in different ranks enlarged at comparable rates, although the rates from one ear to the next along the stem differed. In both tassels and ears, spp divide to form paired sessile and pedicellate spikelet primordia when the spp is 150 μm wide; ear axes are significantly thicker than tassel axes at the time of bifurcation. The similarities in growth between ear and tassel primordia lend further support to the hypothesis that both the maize tassel and ear are derived from a common inflorescence pattern, a pattern shared with teosinte. Inflorescence primordial growth also suggests that a key character difference between teosinte and maize, distichous vs. polystichous arrangement of spikelets, may be related to size of the apical dome and/or rate of primordium production by the apical meristem. There appears to be more than a single morphological event in the shift from vegetative to reproductive growth. The evocation of axillary buds (ears) is independent of, and temporally separated from, the transition to flowering at the primary shoot apex (tassel).

The control of maize spikelet meristem fate by the APETALA2-like gene indeterminate spikelet1

“…The development of a critical meristem size in maize is thought to provide the cue for branching to occur (Sundberg and Orr 1996). One mechanism by which IDS1 may suppress indeterminate growth is to restrict the size of the residual spikelet meristem such that it can no longer initiate florets.…”

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

“…and A.R.O. ), quoted earlier, was based on published light micrographs ( Bonnett, 1940( Bonnett, , 1948( Bonnett, , 1953 of maize and our own published and unpublished scanning electron micrographs of various maize cultivars, including Chapalote, illustrating organogenetic development of ear infl orescences ( Sundberg et al, 1995 ;Sundberg and Orr, 1996 ). In a study of vascular development of the maize tassel in the landrace Chapalote, we (TDP and MDS) noticed an unusual alternating pattern of elongation and suppression of leaf bases in the transition region between vegetative to reproductive growth.…”

“…The phyllotactic pattern of husk leaf primordia on young ears was determined from specimens of Zea mays landrace Chapalote previously prepared for scanning electron microscopy (SEM) ( Sundberg and Orr, 1996 ) and from freshly harvested seedlings. A total of 20 critical-point-dried specimens, already mounted on aluminum stubs, were examined with a Nikon (Melville, New York, USA) SMZ-2T stereomicroscope; freehand sketches recorded the placement of husk leaves or the bases of dissected husk leaves.…”

“…In the latter mechanism, a four-rowed distichous (two-ranked) infl orescence primordium is converted into a polystichous eight-rowed (four-ranked) infl orescence via a second bifurcation of spikelet primordia instead of only one bifurcation event prior to spikelet primordia converting into spikelet pair primordia and subsequently into sessile and pedicellate spikelets. Later, we suggested, " It seems likely … that the primary mechanism responsible for the shift from distichy to polystichy during the evolution of maize may have involved the transition from distichous to spiral phyllotaxy, a process that occurs ontogenetically during development of the very young infl orescence meristems " ( Sundberg and Orr, 1996, pp. 1264-1265.…”

“…In Benz ' s material, row number varied from eight (four-ranked) to 12 rows (six-ranked). In a previous study of infl orescence development in Chapalote ( Sundberg and Orr, 1996 ), row number varied from four (distichous) to eight (polystichous) Thus, Chapalote [Vol. 95 Homogeneity of variance in leaf base thicknesses was tested using the F max test ( Sokal and Rohlf, 1981 ).…”