ISSN 10214437, Russian Journal of Plant Physiology, 2015, Vol. 62, No. 4, pp. 480–486. © Pleiades Publishing, Ltd., 2015.
Drought is considered as one of the most important
environmental stresses limiting plant growth and crop
productivity. Water stress can be defined as the absence
of adequate soil moisture necessary for a plant to grow
normally and complete its life cycle. Common plant
symptoms to water deficit are stunt growth, limit
diffusion to chloroplasts because of stomata closure,
reduce photosynthesis rate and accelerate leaf senes
One of the biochemical changes occurring in plants
when subjected to water stress is the accumulation of
ROS (reactive oxygen species) . Chloroplasts,
mitochondria, and peroxisomes in plant cells are
important intracellular generators of ROS, which can
be responsible for the occurrence of oxidative damages
under abiotic stress . Increasing evidences suggest
that water stress induces oxidative stress in various
The article is published in the original.
plants , including both free radical (superoxide rad
icals, hydroxyl radical, perhydroxy radical and alkoxy
radicals) and nonradical (molecular) forms (hydro
gen peroxide and singlet oxygen), which can destroy
proteins, lipids, carbohydrates and nucleic acids .
Plants can respond to osmotic stress at morphological,
anatomical and cellular levels with modifications that
allow the plant to avoid the stress or to increase its tol
erance . The induction of ROSscavenging
enzymes, such as superoxide dismutase (SOD), per
oxidase (POD), ascorbate peroxidase (APX), catalase
(CAT) and other compounds such as carotenoids,
ascorbic acid, thiols, soluble protein and glutathione
are the most common mechanism for detoxifying
ROS synthesized during stress .
Plants under water stress also produce large amounts
of amino acids, such as proline for improving drought
resistance. Proline prevents oxidation inside the cells
under drought stress . Damage to fatty acids of mem
brane could produce small hydrocarbon fragments
including MDA. MDA is the final product of plant cell
membrane lipid peroxidation and is an important sign
of membrane system injury .
Biochemical and Physiological Responses of
to Humic Acid Under Water Stress
, P. GharaviKouchebagh
, and H. Khoshvaghti
Department of Agriculture, Payame Noor University (PNU), Iran
Department of Plant Ecophysiology, Faculty of Agriculture, University of Tabriz, Tabriz, Iran
Received October 22, 2014
—This study examines the effects of humic acid (HA, control, 3 and 6 mg/L) on some biochemical
and physiological parameters of rapeseed (
L.) plants under different water supply conditions
(60, 100, and 140 mm evaporation from class A pan). Water stress decreased chlorophyll
) and total
) content in plants but proline content partly increased with increasing water stress severity.
Plants treated by HA had more Chl
content under both well and limited water conditions. Appli
cation of HA improved the PSII and peroxidase activity of rapeseed plants under all irrigation treatments.
Ascorbate peroxidase activity under severe water stress condition increased by 70 and 95%, compared with
that under moderate and well watering conditions, respectively. Catalase activity was 51 and 69% less under
well watering than that of moderate and severe water stress conditions, respectively. The highest activity of
ascorbate peroxidase was recorded in plants treated by 6 mg/L HA. HAtreated plants had 42, 8.5, and 15%
more soluble protein content under well watering, moderate and severe water stress conditions, respectively,
compared with control plants. Malondialdehyde increased with increasing the severity of water stress, in con
trast, application of HA significantly reduced the amount of this trait under water stress conditions. It was
shown that application of HA increased the activity of antioxidant enzymes, improved PSII activity and con
sequently decreased lipid peroxidation in rapeseed plants.
Keywords: Brassica napus,
antioxidant enzymes, chlorophyll content, humic acid, lipid peroxidation, pro
line, PSII activity, water stress
: APX—ascorbate peroxidase; CAT—catalase;
—total chlorophyll; HA—humic acid;
POD—peroxidase; MWS—moderate water stress; SWS—severe
water stress; WWC—well watering conditions.