Normal and Abnormal Development in the Arabidopsis Vegetative Shoot Apex.

Abstract

Vegetative development in the Arabidopsis shoot apex follows both sequential and repetitive steps. Early in development, the young vegetative meristem is flat and has a rectangular shape with bilateral symmetry. The first pair of leaf primordia is radially symmetrical and is initiated on opposite sides of the meristem. As development proceeds, the meristem changes first to a bilaterally symmetrical trapezoid and then to a radially symmetrical dome. Vegetative development from the domed meristem continues as leaves are initiated in a repetitive manner. Abnormal development of the vegetative shoot apex is described for a number of mutants. The mutants we describe fall into at least three classes: (1) lesions in the shoot apex that do not show an apparent alteration in the shoot apical meristem, (2) lesions in the apical meristem that also (directly or indirectly) alter leaf primordia, and (3) lesions in the apical meristem that alter meristem size and leaf number but not leaf morphology. These mutations provide tools both to genetically analyze vegetative development of the shoot apex and to learn how vegetative development influences floral development.

A Division in PIN-Mediated Auxin Patterning during Organ Initiation in Grasses

“…We examined the cell division planes in the Brachypodium spikelet meristem and found that the outer two cell layers in the meristem apex, L1 and L2, are dominated by anticlinal divisions (Figure S4). This suggests that, similar to wheat and Arabidopsis [42], [43], Brachypodium has a two-layered tunica. Cell divisions in the tunica layers that are parallel to the meristem surface (periclinal) mark the beginning of leaf morphogenesis, and allowed us to easily identify incipient lemma primordia [44] (Figure S4, arrows).…”

Expression of fasciation mutation in apical Meristems of Soybean, Glycine Max (Leguminosae)

“…The calyx lobes arose first and formed the calyx tube (Figs. The fuf mutation did not cause detectable alteration in meristem zonation nor the shape and differentiation of vegetative organs, but it produced club-shaped siliques (Medford et al, 1992). 26).…”

“…The subsequent differentiation of floral organs in the fasciation mutants was analogous to normal flower development. formative region (Medford, 1992). 25, 27), and the next whorl formed was the petals whose primordia alternated with the lobes of the calyx (Fig.…”

“…ly postgermination stage-In this study, the apical meristem was defined as the portion of tissue distal and cen-tric to the last visibly formed leaf primordium (Steeves and Sussex, 1989;Medford, 1992;Fosket, 1994). The developmental stage of the apical meristem was determined by the size of the leaf primordium.…”

Plasmodesmata

“…When injected into a single cell,its movement to neighbouring cells reveals the symplasmic pathways open for the diffusion of small metabolites, hormones and other regulators. Similarly, the Arabidopsis mutants Fey and Dip which early in development loose the ability to maintain a central undifferentiated AM area (Medford et al 1992), might be impaired in the mechanism which closes the plasmodesmata at the field boundaries. 7).…”