Cell-lineage patterns in the shoot apical meristem of the germinating maize embryo

Abstract

A fate map for the shoot apical meristem of Zea mays L. at the time of germination was constructed by examining somatic sectors (clones) induced by γ-rays. The shoot apical meristem produced stem, leaves, and reproductive structures above leaf 6 after germination and the analysis here concerns their formation. On 160 adult plants which had produced 17 or 18 leaves, 277 anthocyanin-deficient sectors were scored for size and position. Sectors found on the ear shoot or in the tassel most often extended into the vegetative part of the plant. Sectors ranged from one to six internodes in length and some sectors of more than one internode were observed at all positions on the plant. Single-internode sectors predominated in the basal internodes (7,8,9) while longer sectors were common in the middle and upper internodes. The apparent number of cells which gave rise to a particular internode was variable and sectors were not restricted to the lineage unit: a leaf, the internode below it, and the axillary bud and prophyll at the base of the internode. These observations established two major features of meristem activity: 1) at the time of germination the developmental fate of any cell or group of cells was not fixed, and 2) at the time of germination cells at the same location in a meristem could produce greatly different amounts of tissue in the adult plant. Consequently, the developmental fate of specific cells in the germinating meristem could only be assigned in a general way.

Growth from two transient apical initials in the meristem ofSelaginella kraussiana

“…Historically, the concept of monoplex apices has been linked to the notion of a slowly dividing persistent apical cell (Newman, 1965). By contrast, complex meristems of seed plants have a small number of impermanent apical initials in each layer (Bossinger et al, 1992;Dulieu, 1969;Furner and Pumfrey, 1992;Irish and Sussex, 1992;Jegla and Sussex, 1989;Korn, 2001;McDaniel and Poethig, 1988). Our data clearly show that apical initials in the S. kraussiana apex are impermanent and thus it is reasonable to propose that mechanisms that regulate initial cell activity may be conserved in vascular plants.…”

Maize YABBY Genes drooping leaf1 and drooping leaf2 Regulate Plant Architecture

“…Within the meristem, founder cells for the incipient leaf primordium are recruited in concert with those of the subtending internode and its associated axillary meristem (Sharman, 1942;McDaniel and Poethig, 1988). Together, these vegetative organs comprise a repeating unit of the shoot called a phytomer (Galinat, 1959), and the developmental interval of iterative, phytomer initiation is called a plastochron (Lamoreaux et al, 1978).…”

Germline replications and somatic mutation accumulation are independent of vegetative life span inArabidopsis

“…The primary origin of all above-ground tissues of a plant is a dome-like structure named the shoot apical meristem (SAM). These cell-fate analyses have demonstrated that stem cells within the SAM do not have predetermined fates but give rise to organs in a probabilistic way based on their location within this stem-cell niche (20)(21)(22)(23). In Arabidopsis, it is estimated that two to four genetically effective cells (GEC) in the dry seed are the progenitors of late rosettes as well as flowers (20,21,24).…”