ISSN 10214437, Russian Journal of Plant Physiology, 2012, Vol. 59, No. 4, pp. 530–545. © Pleiades Publishing, Ltd., 2012.
Original Russian Text © V.V. Choob, A.A. Sinyushin, 2012, published in Fiziologiya Rastenii, 2012, Vol. 59, No. 4, pp. 574–590.
It is believed that one of the first descriptions of the
phenomenon of fasciation is the work of Gerard .
The term “fasciation” (from the Latin fascia – strip)
for a long time had an interpretative manner: enlarged
meristem, change in the stem shape and the number of
developing leaves were considered as a result of several
shoot fusion. Mutants with fasciated stems often have
also fasciated flowers. Such phenomenon was
described for some mutants of
The phenomenon of fasciation embraces diverse
anatomomorphological modifications of stems and
flowers: isodiametric expansion (radial fasciation),
flattening and the appearance of ridges (linear fascia
tion), splitting of the mass of meristematic cells into
autonomic meristems (defasciation) . Fasciation is
often accompanied by the increase in the number of
leafy organs and a characteristic disturbance in orga
notaxis, i.e., a disturbance in the positional control of
The mechanisms of positional control are realized
on the level of organ initiation within shoot apical
meristem (SAM) or floral meristem (FM) . Recent
decades are characterized by a growing stream of
papers on the regulation of proliferative activity and
morphogenesis in SAM and FM (for example ).
Each of the elements of the regulation is associated
with one of the members of the family of factors that
are more or less duplicate the functions of each other,
producing the crossing alternative pathways of signal
ing [9, 10]. However, data on the interaction between
these pathways in the space are still fragmentary. Thus,
the interaction between moleculargenetic processes,
positional control, and observed anatomomorpho
logical changes characteristic of fasciated plants is still
not well described in the literature. This review is
designed to fill this gap.
Zones of the Shoot Apical Meristem
For apical meristems, a definite mitotic spindle
orientation is characteristic, which depends on the
relative position of initials. In most flowering plants, in
the outer layers only anticlinal divisions occur (the
spindle is parallel to the surface, and the forming cell
wall is perpendicular to the surface) [11, 12].
Shoot apical meristem (SAM) comprise tunica
from several cell layers. The number of layers may vary
from 0 to 6 ; however, usually tunica is composed
of three layers: L1, L2, and L3. In the internal cell lay
ers, spindle orientation is not constant; all these cells
belong to the corpus [11, 12]. The part of the meristem
containing corpus initials is called the ribzone  or
medullar zone  (Fig. 1).
Flower and Shoot Fasciation: from Phenomenology
to the Construction of Models of Apical Meristem Transformations
V. V. Choob and A. A. Sinyushin
Department of Biology, Moscow State University, Moscow, 119992 Russia;
Received June 29, 2011
—The review considers the phenomenon of fasciation arising due to the enlargement of shoot or flo
ral meristem. The system of CLAVATA–WUSCHEL proteins controls the pool of stem cells in the surface
layers of the shoot apical meristem. The analysis of the literature allowed clarifying the role of the
) gene in the creation of positional signals for the emergence of leaf primordia and procambial strands.
The hypothesis is put forward about the new regulatory cascade PINHEAD/ZWILLE–WUSCHEL involved
in the positional control of auxin fluxes and determining the optimal density of vascular bundles in the tissue
volume. The examples of various types of shoot and flower fasciation are presented: radial, linear, and ring
fasciation, defasciation). The model of anatomomorphological changes accompanying fasciation is sug
: higher plants, morphogenesis; shoot apical meristem; positional information, stem cells, fascia
tion, floral meristem.
: FM—floral meristem; LRR—leucinerich repeat;
SAM—shoot apical meristem.