ISSN 1062-3604, Russian Journal of Developmental Biology, 2016, Vol. 47, No. 4, pp. 207–215. © Pleiades Publishing, Inc., 2016.
Original Russian Text © E.A. Bykova, D.A. Chergintsev, T.A. Vlasova, V.V. Choob, 2016, published in Ontogenez, 2016, Vol. 47, No. 4, pp. 235–243.
Effect of the Auxin Polar Transport Inhibitor on the Morphogenesis
of Leaves and Generative Structures during Fasciation
in Arabidopsis thaliana (L.) Heynh.
E. A. Bykova, D. A. Chergintsev, T. A. Vlasova, and V. V. Choob
Faculty of Biology, Moscow State University, Moscow, 119234 Russia
Received October 7, 2015; in final form, December 18, 2015
Abstract—An increase in the proliferative activity of a shoot apical meristem (SAM) and the further accumu-
lation of a pool of undifferentiated cells (fasciation) results in phyllotaxis changes. In the case of Arabidopsis
thaliana, a typical spiral leaf arrangement is replaced by an opposite or verticillate one (depending on the level
of a fasciation manifestation). Pistil development in mutant plants is accompanied by the appearance of a
group of undifferentiated meristematic cells in its central part. The addition of N-1-naphthylphthalamic acid
(NPA) causes an increase in the meristem volume and number of stipules in both mutant and control plants.
The NPA effect on the f loral morphogenesis results in a significant growth of meristemic cell pool. The inter-
action of different mechanisms of a meristem volume control is discussed.
Keywords: SAM, NPA, fasciation, blastozone, A. thaliana
The shoot apical meristem (SAM) of flowering
plants contains a pool of undifferentiated cells located
in the central zone and waiting meristem (organizing
center), whereas basic morphogenetic processes occur
in a functionally separated peripheral zone (Fletcher
and Meyerowitz, 2000; Dodsworth, 2009; Xie et al.,
2009; Choob and Sinyushin, 2012). The mechanisms
of maintenance of this pool are now intensively stud-
ied using Arabidopsis thaliana (L.) Heynh. as a model
object, and the existence of a CLAVATA–WUSCHEL
negative feedback system controlling the size of the
pool of undifferentiated cells has been demonstrated
(Dodsworth, 2009; Nieminen et al., 2015). However,
in addition to this regulation system, there are some
other mechanisms to control the meristem volume.
For example, the study of a NANA gene influence on
the SAM proliferative activity showed that, during the
plant transition to the reproductive stage, this gene
begins to control the SAM activity significantly later
than the CLV–WUS system and acts independently of
this system (Albert et al., 2014).
The WUS transcription factor is synthesized in the
SAM organizing center and then transported to the
surface layer of the SAM central zone via plas-
modesms. Interacting with the promoter of the CLV3
gene, WUS enhances the expression of this gene
(Yadav et al., 2011). A CLV3 propeptide is proteolyti-
cally processed, modified, glycosylated, and then
secreted as a short glycopeptide (13 amino acids). A
short CLV3 peptide is able to bind to a receptor com-
plex consisting of the CLV1 and CLV2 proteins (Xie
et al., 2009; Ohyama et al., 2009) that result in a
decreased WUS expression.
Failures in the expression of any genes involved in
the control of a SAM proliferative activity control via
this system, cause either decrease (wus mutation) or
increase (clv1, clv2, and clv3 mutations) of the undif-
ferentiated cell pool that correlatively influences on
the size of a peripheral zone, in which the prepattern-
ing and the further formation of leaf primordial occur
(Bykova et al., 2013).
As a plant grows, its meristem forms a large number
of anlages. However, the development of any organ in
a certain location of a peripheral zone is preceded by a
prepatterning, which, in turn, is determined mainly by
the redirection of the auxin flow from the surface lay-
ers to the forming organ (Berleth et al., 2007; Choob,
2010). This primary auxin flow serves as a guide for the
further formation of procambium and conducting
bundles in a stem or a primary rib in a leaf.
There are some positioning control mechanisms
that provide the separation of two neighboring leaf pri-
mordia from each other. In the case of the auxin polar
transport violation, these mechanisms become
weaker, which results in the appearance of merged
leaves or leaves with several equivalent primary ribs.
Such polar transport violation is typical for PIN
DEVELOPMENTAL BIOLOGY OF PLANTS