ISSN 10214437, Russian Journal of Plant Physiology, 2012, Vol. 59, No. 6, pp. 828–832. © Pleiades Publishing, Ltd., 2012.
Original Russian Text © A.P. Smolov, G.A. Semenova, N.Yu. Minakova, A.M. Butanaev, G.N. Shirshikova, 2012, published in Fiziologiya Rastenii, 2012, Vol. 59, No. 6, pp. 781–785.
It was long known that it is ammonium that is used
to synthesize the first nitrogencontaining organic
compounds, amino acids , whereas nitrate can be
assimilated only after it is reduced to ammonia .
The main role of ammonium in plant cell metabolisms
can therefore be assumed to be a substrate in ketoacid
amination, that is, in amino acid synthesis.
We previously studied the effect of exogenous
ammonium on mixotroph soybean callus cells and
found that even small, below 0.1 mM ammonium
concentrations caused manifold (5–10 times)
increase in the number of ribosomes  and facilitated
the increase in the amount of membranous structures
in chloroplasts and mitochondria . This pointed to
some other, “nonsubstrate” function of ammonium
related to the assembly and functioning of the cellular
proteinsynthesizing machinery, ribosomes. But in
vitro cell culture is an artificial model system, and its
metabolic processes are not always fully identical to
the processes taking place in the in vivo plants. It
remains unclear whether the nonsubstrate function of
ammonium is featured by other plant systems.
Since ammonium absorbed by the higher plant
roots can be transported in the aboveground organs
both as ions and amines of organic compounds pro
duced in the root cells [1, 2], it is difficult to estimate
its effects on ribosome synthesis and function in the
The cell suspension of green unicellular alga
could be a more suitable
system to confirm or disprove the hypothesis of the
nonsubstrate ammonium function. Besides, since the
algal genome is known quite well, there is a possibility
to estimate the effects of ammonium on the expression
of genes for ribosomal components.
The ribosome biogenesis is a multistep process .
It takes place in steps in different cellular compart
ments: in the nucleolus, nucleoplasm, and cytoplasm.
Many different constituents with their list constantly
growing participate in it at its every step, from expres
sion of the corresponding genes to the production of
the functional organelle . It is possible that the
exogenous ammonium discovered by us to cause the
manifold growth in the ribosome number per cell also
has an effect on the ribosome biogenesis.
Thus, the aim of this work was the analysis of
ammonium treatment effects on the content of pro
tein, chlorophyll, and ribosomal structures as well as
mRNA coding for the small subunit protein
rps6 and the content of 18S rRNA as parts of the ribo
Effects of Ammonium Treatment on the Protein and Chlorophyll
Contents and the Number of Ribosomes in
A. P. Smolov
, G. A. Semenova
, N. Yu. Minakova
, A. M. Butanaev
, and G. N. Shirshikova
Institute of Basic Biological Problems, Russian Academy of Sciences,
Institutskaya ul.2, Pushchino, Moscow oblast, 142290 Russia;
Institute of Theoretical and Experimental Biophysics, Russian Academy of Sciences, Pushchino,
Moscow oblast, 142290 Russia
Received October 8, 2011
—The effects of exogenous ammonium on total protein and chlorophyll contents and the number
of ribosomes in
(Sager) green alga cells were studied. The absence of ammonium
from nutrient medium resulted in a twofold drop in the number of ribosomes in the cytoplasm. The chloro
phyll content of the cells grown on ammoniumfree nitratecontaining medium insignificantly increased.
The increase in the ribosome number in the presence of exogenous ammonium was not accompanied by the
elevation of total cellular protein and did not depend on the levels of mRNA of rps6, a small ribosome subunit
protein, and the 18S rRNA. Possible reasons for the effect of exogenous ammonium during ribosome biogen
esis are discussed.
Keywords: Chlamydomonas reinhardtii
, ammonium, protein, chlorophyll, ribosomes, ribosomal genes