ISSN 10214437, Russian Journal of Plant Physiology, 2011, Vol. 58, No. 5, pp. 936–940. © Pleiades Publishing, Ltd., 2011.
Original Russian Text © L.V. Kravchenko, A.I. Shapozhnikov, N.M. Makarova, T.S. Azarova, K.A. L’vova, I.I. Kostyuk, O.A. Lyapunova, I.A. Tikhonovich, 2011, published in Fiz
iologiya Rastenii, 2011, Vol. 58, No. 5, pp. 781–786.
Compound secretion from the roots into the ambi
ent medium is a normal manifestation of plant life .
When wheat aboveground organs (leaves) were
exposed during the entire growth period to
approximately 45% of carbon transported to the roots
was secreted by them into soil . For 90 days of
growth under nonaxenic conditions, various grasses
secreted 8–15% of fixed carbon . Active role of
roots in metabolic processes resulting in the synthesis
of complex compounds from absorbed ions and pho
tosynthates coming from leaves play a substantial role
for the life of plants and soil microorganisms . The
term “root exometabolites” embraces a wide set of
organic and inorganic molecules and ions [4, 5].
Among them are organic acids, sugars, oligo and
polysaccharides, peptides, and secondary metabolites.
These compounds could affect growth of neighboring
plants  or rhizospheric microorganisms. For exam
ple, compounds with the action character similar to
bacterial signals of quorum sensing , specific signal
ing molecules—inducers of legume–rhizobium sym
biosis  and mycorrhiza development  can be
Lowmolecularweight organic compounds con
tribute markedly into root exometabolites secreted to
rhizosphere. Among them are carbohydrates, organic
acids, and amino acids. Carbohydrates and organic
acids are the main trophic compounds for rhizo
spheric microorganisms. Root exometabolites deter
mine largely the integration of microorganisms and
plants and functioning of the plant–microbial system.
It is shown that diploid wheats, differing from hexap
loid ones by increased content of organic acids in root
exudates, provided for the accumulation of associated
nitrogenfixing and other rhizobacteria in their rhizo
sphere . Breeding programs are known to be
directed to the producing genotypes releasing more
exometabolites . Such genotypes are believed to be
potentially more adapted to environmental stresses
and application of biopreparations with rhizospheric
microorganisms. Production of such genotypes
requires a deep studying crop root exudates. However,
in spite of a great number of studies on the root
exometabolite composition, so far we are rather lim
ited in knowledge of the species and cultivar specificity
of their molecular composition and dynamics of root
exudation in various crops. Quantification of root
exometabolites is a difficult methodological task
because of a diversity and small concentrations of
these compounds and also the avoiding the influence
of other microorganisms utilizing root exudates .
The objective of this work was the analysis of the
composition of organic acids, carbohydrates, and
amino acids in root exudates of wheat and tomato.
MATERIALS AND METHODS
Experiments were performed with economically
valuable plants differing in their taxonomy and physi
Exometabolites of Bread Wheat and Tomato Affecting
the Plant–Microbe Interactions in the Rhizosphere
L. V. Kravchenko
, A. I. Shapozhnikov
, N. M. Makarova
, T. S. Azarova
, K. A. L’vova
I. I. Kostyuk
, O. A. Lyapunova
, and I. A. Tikhonovich
AllRussia Research Institute for Agricultural Microbiology, Russian Academy of Agricultural Sciences,
sh. Podbel’skogo 3, Pushkin8 and St. Petersburg, 196608 Russia;
Vavilov Institute of Plant Industry, Russian Academy of Agricultural Sciences, Bol’shaya Morskaya ul. 42,
St. Petersburg, 190000 Russia
Received February 22, 2011
—The composition of organic acids, carbohydrates, and amino acids released by the roots of wheat
L., cv. Obelisk) and tomato (
L., cv. Carmello) was examined.
Tomato roots released threefold more organic acids, sevenfold more tyrosine, 3.8fold more threonine, and
2.8fold more arginine that wheat roots; in contrast, wheat roots released 4.1fold more tryptophan than
tomato roots. Differences in the ratio between organic acids and sugars and also in the intensity of Ltryp
tophan release could affect the interaction between tested plants and microorganisms in their rhizosphere.
Keywords: Triticum aestivum, Lysopersicon esculentum
, root exudates, plant–microbe systems.