1022-7954/01/3711- $25.00 © 2001
Russian Journal of Genetics, Vol. 37, No. 11, 2001, pp. 1275–1278. Translated from Genetika, Vol. 37, No. 11, 2001, pp. 1517–1521.
Original Russian Text Copyright © 2001 by Kholodar, Sidorova, Shumny.
Development and functioning of the legume–rhizo-
bium symbiosis require a well-developed regulation on
the part of both macro- and microsymbiont. Therefore,
phytohormones play an important role in the integra-
tion of physiological processes in the host plant and
root-nodule bacteria. There is much evidence that phy-
tohormones affect the formation and development of
root nodules, and inoculation of legumes with root-
nodule bacteria changes their hormonal status [1–4].
Even at the earliest stages of symbiosis formation, phy-
tohormones play a substantial role. For example, trans-
genic white clover exhibits an increased expression of
auxin-stimulated genetic loci as soon as 30 h after inoc-
ulation with root-nodule bacteria, which reﬂects an
increased auxin activity in the roots . Other authors
observed an increased auxin level in the pea roots; this
value reached maximum on the 4th to 6th day after
inoculation and then decreased by the 11th day. In the
roots of uninfected plants, the auxin level changed
insigniﬁcantly . The results of this study also demon-
strated that the change in the auxin level in the course
of nodulation depended on the macrosymbiont’s geno-
type. Different types of pea symbiotic mutants had dif-
ferent sensitivities to synthetic auxin 2,4-D .
inoculation causes short-term local inhibition of the
acropetal auxin transport in the white clover roots .
Phytohormones other than auxin also play a certain
role in nodulation. Several authors reported on the
interaction between the plant’s genotype and the quali-
tative composition of endogenous cytokinins, as well as
the change in the macrosymbiont’s sensitivity to exog-
enous cytokinin after inoculation with root-nodule bac-
teria [6, 8].
There is evidence that another phytohormone, eth-
ylene, inhibits nodulation in some legumes, including
pea . Conversely, inhibitors of ethylene synthesis
stimulate nodulation of pea [10, 11]. In alfalfa, which
responds to ethylene in the same way as pea does, an
ethylene-insensitive mutant was isolated. This mutant
was characterized by supernodulation .
There are few published data on the levels of gibber-
ellins and abscisic acid in the macrosymbiont during
the nodulation period. The authors of the published
studies available observed an increased gibberellin
level and a decreased abscisic acid level in this period
Note that, so far, the hormonal balance in the mac-
rosymbiont has only been studied at the initial stages of
nodulation. However, it is important to clarify the pos-
sible effect of mature nitrogen-ﬁxing nodules on the
hormonal status of a leguminous plant. The purpose of
this study was to analyze the hormonal status of pea
symbiotic mutants differing from one another in nodu-
lation and to determine the effect of rhizobium infec-
tion on the levels of phytohormones in the macrosym-
MATERIALS AND METHODS
In the ﬁrst experiment, three symbiotic mutants
induced from the cultivar Ramonskii 77 were used as
the original material. These were the non-nodulating
K20a mutant, the K287/1 mutant with ineffective nod-
ules, and the supernodulating K301 mutant. In the sec-
ond experiment, we studied the cultivar Rondo and six
symbiotic mutants, including four supernodulating
, K9a/1, K10a, and K21a) mutants and two
mutants with single nodules (K17a and K18a), which
had the phenotype nod–/+. The morphological, biolog-
ical, and genetic characteristics of these mutants were
described earlier [13–15].
The experiment was performed in a greenhouse.
Keramzit and the standard nutrient solution were used
Phytohormone Levels in Different Types
of Symbiotic Mutants of Pea
A. V. Kholodar, K. K. Sidorova, and V. K. Shumny
Institute of Cytology and Genetics, Siberian Division, Russian Academy of Sciences,
Novosibirsk, 630090 Russia; fax: (3832) 33-12-78; e-mail: firstname.lastname@example.org
Received March 29, 2001
—The levels of the phytohormones auxin and gibberellin were studied in the original pea (
L.) cultivars Rondo and Ramonskii 77 and in different types of symbiotic mutants (non-nodulating, with
single nodules, and supernodulating) induced from them. The results obtained indicated that the levels of the
phytohormones in the symbiotic mutants depend on the plant’s genotype, developmental phase, and infection
with rhizobia. Two mutants were isolated whose phytohormonal status markedly differed from the original forms.
These mutants may be used for identiﬁcation of the genes that determine the auxin and gibberellin statuses.