ISSN 10214437, Russian Journal of Plant Physiology, 2010, Vol. 57, No. 6, pp. 770–777. © Pleiades Publishing, Ltd., 2010.
Original Russian Text © A.A. Ivanov, 2010, published in Fiziologiya Rastenii, 2010, Vol. 57, No.6, pp. 826–834.
Soil salinization is one of the main factors restrict
ing plant dissemination and suppressing such key met
abolic processes as photosynthesis , photorespira
tion, production of amino acids and carbohydrates.
Salinization induces osmotic stress accompanied by a
reduction in water uptake by the plants and therefore
by stomata closing, which results in a decrease in
uptake and suppression of photosynthesis .
Plant tolerance to salt stress depends on a complex
of interrelated systems ensuring plant adaptation on
metabolic and gene levels including ionic homeosta
sis, synthesis of osmolytes, compartmentation of toxic
ions, and structures preventing the generation of reac
tive oxygen species (ROS) .
The maintenance of ionic homeostasis and water
potential in the cytosol and intracellular compart
ments under salt stress depends on a regulated opera
tion of proton pumps, ion channels, and transporters
 ensuring efflux of
cytosol to the apoplast by means of
located in the plasma membrane  and accumula
in the vacuole via
Efficiency of ion exchange depends on the value of
transmembrane proton gradient produced by Ptype
ATPase in the plasma membrane and vacuolar V
ATPase together with vacuolar
The accumulation of numerous charged particles
in the vacuole upsets the intracellular osmotic equilib
rium. The synthesis and accumulation in the cytosol of
organic osmolytes, such as proline, may be considered
as a compensating mechanism restoring the upset
equilibrium between the cytosol and vacuole . In
addition to osmolytic, proline can fulfill other func
tions, such as inactivation of hydroxyl radicals, the
maintenance of the balance between light absorption
related to photosynthesis and NADH utilization asso
ciated with carbon fixation, and be a source of reduc
ing equivalents upon metabolic imbalance weakening
the damaging effect of the stress . Proline can act as
a regulator of gene expression, governing the osmotic
response, and some researchers look upon proline as a
salt stressdependent signal compound .
At high concentrations, NaCl can directly suppress
photosynthesis as a result of oxidative stress, leading to
production of ROS possessing a high reactivity and
inducing damage to membranes, proteins, and DNA
. Upon the absorption of sunlight, production of
ROS in the chloroplasts can occur as a result of
photoreduction with the formation of superoxide
(Mehler’s reaction) or by means of interaction
Effect of Light Conditions of Wheat Growing on Sensitivity
of Photosynthetic Machinery to Salt Stress
A. A. Ivanov
Institute of Fundamental Problems of Biology, Russian Academy of Sciences,
Institutskaya ul. 2, Pushchino, Moscow oblast, 142290 Russia;
Received October 16, 2009
—Sensitivity of wheat (
L.) seedlings to salt stress was investigated as dependent on
light conditions of plant growing. In twoweekold seedlings grown on saltfree medium, aboveground organs
were detached from the roots and subjected to a brief stress at different concentrations of NaCl. The extent
of salt stress effect expressed as a decrease in the rate of the photosynthetic release of oxygen and the relative
content of water and chlorophyll in the leaves greatly depended on light conditions of growing. The plants
grown at low light intensity were notable for a greater sensitivity to NaCl in the medium. Plant responses to
salt stress were different at low and high salt concentrations. At low NaCl concentrations (0.05–0.10 M) in
the solution, in plants grown at low light intensity, the rate of photosynthesis calculated per unit of chlorophyll
increased. This effect was not observed in plants grown at the higher light intensity. At high NaCl concentra
tions (0.2–0.4 M) in the medium, the rate of photosynthesis rapidly decreased in all the types of treatment,
with the effect being most pronounced in plants grown at low light intensity. The obtained results suggest a
narrow range of NaCl concentrations with an optimum at 0.1 M positively affecting the wheat seedlings phys
iological state upon salt stress development depending on light conditions of plant growing.
Triticum aestivum, salt stress, NaCl, oxygen evolution, chlorophyll, relative water content.
: PSII—photosystem II; RWC—relative water content.