Аннотация:THE IMPACT OF SHOOT APICAL MERISTEM SIZE
ON THE STRUCTURE OF COMPOUND LEAF
IN FASCIATED MUTANTS OF Pisum sativum
Ekaterina A. Bykova, Vladimir V. Choob
Lomonosov Moscow State University, Moscow, Russia
katebykova.90@mail.ru
The rate of cell division in the central zone of shoot apical meristem depends on signaling cross talk between the rib-zone and upper layers of tunica.
Any disturbance of this interaction leads to a change in the number of cells in the
meristem. The phenomenon of significant intensification of cell division and consequent increasing of meristem size is called fasciation (Choob, Sinyushin, 2012).
This process often occurs via the enrichment of stem cell pool in the central zone
of the meristem.
During formation of any organ primordia, the meristem ‘allocates’ a certain
number of cells, whose fate is rather strictly programmed. It is logical to assume
that due to an increase of the cell number in the meristem, the ‘allocated’ cell
pool can correlatively change, leading to modifications in organ morphology and
arrangement.
In previous papers (Gourlay et al., 2000; Bykova et al., 2015) devoted to
manifestations of fasciation in P. sativum, the ‘allocated’ portion of meristematic
cells intended for the development of a single compound leaf (including its
base and stipules) was designated as a blastozone. In the present study, we used
seedlings of two fasciated mutant lines of pea: “Shtambovy” and “Rosacrone”.
Wild type plants of “Nemchinovskiy–766” variety served as control (isogenic
to “Shtambovy”).
Anatomical analysis of cells of the shoot apical meristem (SAM) of
“Shtambovy” revealed ultrastructural features: irregular thickness of the cell walls
and a large number of vesicles with electron dense loose inclusions, which were
not characteristic of SAM of non-fasciated plants.
In fasciated mutants of pea, the number of leaflets and tendrils of the compound leaf did not change. These numbers increased gradually, depending on the
node number, in the same manner as in wild type plants. The changes were only
revealed in rachis and stipule number and arrangement. For example, instead of
single rachis, two rachises per node are formed. This phenomenon is usually accompanied by development of the additional stipules from both sides of the new
rachis. We also recorded incompletely divided stipules in between two rachises of
the same node. However, in some cases, these rachises were not independent: we
often found incompletely fused rachises. All these observations could be explained
by gradual increasing of the blastozone size.
31
Thus, the complexity of leaf structure in certain node could be an indirect
method of blastozone measurement. In order to obtain the direct data on the correlation between the changes in the compound leaf structure and the shoot meristem size, we carried out morphometric measurements of SAM in wild type and
fasciated mutants.
The meristem size in the fasciated line “Rosacrone” increased gradually with
the node number, significantly differing from the similar values in the wild type.
Nevertheless, the differences between the wild type and another fasciated line
“Shtambovy” cannot be unequivocally recognized. At the same time, the plants of
“Shtambovy” exhibit a strong correlation between the maximal linear size of the
meristem and the number of rachises per node. For example, when three rachises
were located on one node, the average linear size of the meristem was 600 μm, if
there was a single rachis on the node, the meristem linear size was approximately
170 μm. The difference is almost three-fold. We have not registered similar correlation in the other fasciated line “Rosacrone” probably because of late manifestation
of fasciation in development (Bykova et al., 2015).
Consequently, as a final conclusion we note that the main impact of the linear
meristem size on the compound leaf structure in pea involves mainly the increase
of rachis and stipules number per node, rather than changes in leaflet and tendril
number.
References
Bykova E.A., Labunskaya E.A., Choob V.V. 2015. Morphological changes in the structure of blastozones during fasciation of Pisum sativum L. and Arabidopsis thaliana (L.) Heynh. Biol.
Bull. 42: 179–185.
Choob V.V., Sinyushin A.A. 2012. Flower and shoot fasciation: from phenomenology to the construction of models of apical meristem transformations. Russ. J. Plant Physiol. 59: 530–545.
Gourlay C.W., Hofer J.M.I., Ellis T.H.N. 2000. Pea compound leaf architecture is regulated by
interactions among the genes UNIFOLIATA, COCHLEATA, AFILA, and TENDRIL-LESS.
Plant Cell 12: 1279–1294.