1062-3604/05/3602- © 2005 Pleiades Publishing, Inc.
Russian Journal of Developmental Biology, Vol. 36, No. 2, 2005, pp. 65–69. Translated from Ontogenez, Vol. 36, No. 2, 2005, pp. 90–95.
Original Russian Text Copyright © 2005 by Penin, Choob, Ezhova.
Among the now used methods of analysis of the
structure of complex characters in plants, the most
effective is the analysis of mutants defective in various
stages of development. This method is most widely
applied to studies of model plants, such as
(L.) Heynh. (fam. Cruciferae) and
L. (fam. Scrophulariaceae). For example,
when studying some mutations leading to changes in
the ﬂower structure of these species, the ABC-model
for determination of ﬂower organ type was developed
(Coen and Meyerowitz, 1991), so-called ABC-model.
However, the formation of terminal ﬂower (indetermi-
nate or terminated type of inﬂorescence) was studied to
a much lesser extent. Hence, the necessity of further
studies is obvious.
MATERIALS AND METHODS
Studies were carried on plants of ecotype
(wild type), mutant
from the collection of
the Department of Genetics, Moscow State University,
terminal ﬂower1-11 (tﬂ1-11)
Biological Resource Center at Ohio State Uni-
versity (ABRC). Plants were grown at long (16 h, LD)
and short (8 h, SD) day conditions. The structure of
ﬂowers was analyzed using SEM. The samples were
prepared as described elsewhere (Ezhova
The position of organs in ﬂowers was analyzed by the
method of diagrams (Eichler, 1875). In order to study
the structure of inﬂorescences of other plant species of
the family Cruciferae, herbarium materials were ana-
lyzed that had been collected in the Volgograd District
in May–July 2002.
RESULTS AND DISCUSSION
Structure of terminal ﬂowers in A. thaliana mutants.
Like the overwhelming majority of species of the fam-
forms indeterminate inﬂo-
rescences. Three main genes are known at present,
which are responsible for the maintenance of the inﬂo-
rescence apical meristem in nondifferentiated state:
(Ezhova and Penin, 2001; Penin, 2003),
TERMINAL FLOWER1 (TFL1)
(Haughn and Sommer-
ville, 1988; Shannon and Meeks-Wagner, 1993), and
TERMINAL FLOWER2 (TFL2)
In mutants defective for these gene functions, inﬂores-
cences of the closed type develop.
More than 90% of the inﬂorescence axes of
mutants were terminalized by a ﬂower; in all other
cases, the proliferative activity of the apical meristem
ceased and terminal ﬂower did not develop.
In lateral ﬂowers of
mutant, the number and
position of organs did not differ from those in wild type
ﬂowers, while the terminal ﬂower underwent some sig-
niﬁcant changes. The number of terminal ﬂower organs
varied: three to ﬁve sepals, two to four stamens, and one
carpel were most frequently formed. As a rule, terminal
ﬂowers had no petals (ca. 50%), but in some cases ﬂow-
ers with four to ﬁve petals were formed (ca. 5%).The
symmetry of the terminal ﬂower perianth was close to
pentameric, unlike tetrameric lateral ﬂowers (Figs. 1a,
1b). The difference in symmetry between the terminal
and lateral ﬂowers is widespread. For example, the ter-
minal ﬂower in
(Coen and Nugent,
1994) is actinomorphic, while lateral ﬂowers are zygo-
morphic. Note that the structure of
DEVELOPMENTAL BIOLOGY OF PLANTS
Basic Principles of Terminal Flower Formation
A. A. Penin, V. V. Choob, and T. A. Ezhova
Moscow State University, Vorob’evy gory, Moscow, 119899 Russia
Received June 9, 2004; in ﬁnal form, July 5, 2004
—Studies of inﬂorescences of the mutants
and double mutant
(L.) Heynh. have shown that the presence of a developed leaf in the node preceding the
terminal ﬂower is a necessary condition for the formation of the terminal ﬂower perianth. This means that peri-
anth cannot develop in an abracteose inﬂorescence of terminal ﬂower. The second necessary condition for the
terminal ﬂower formation is a sufﬁcient level of expression of the genes responsible for ﬂoral morphogenesis.
Combination of these two conditions sufﬁces for the development of a terminal ﬂower with perianth. Since the
general principles of organization are common for the majority of Angiosperms, it can be stated that if the
abracteose inﬂorescence is terminated by a ﬂower with perianth, this is a consequence of displacement of the
lateral ﬂower into the terminal position.
: evolution of inﬂorescences, terminal ﬂower, bractea,
TERMINAL FLOWER1, BRACTEA