Induction of Drought Stress Tolerance by Paclobutrazol and Abscisic Acid in Gingelly (Sesamum indicum L.)

Abstract

For the past several years, several techniques of physiology have been applied to overcome the water deficit and drought stress in field crops. However little information is gained on the response to PBZ and ABA treatments under drought stress and their ameliorative actions on Sesamum. So a study was carried out to understand the effect of PBZ and ABA on drought stress amelioration in Sesamum indicum L. The main aspects studied were the non-enzymatic antioxidant changes in different parts of treated, drought stressed as well as control plants. The non-enzymatic antioxidants (ascorbic acid and tocopherol) were extracted and estimated. The non-enzymatic antioxidant molecules like ascorbate and α-tocopherol showed significant increase under drought condition in Sesamum indicum. PBZ caused significant enhancement in thes e antioxidant enzymes under drought stress and also in well-watered conditions. It is not so with ABA treatment. ABA slightly reduced the non-enzymatic antioxidant contents. From the results, it can be concluded that, these growth regulators are better suited as stress ameliorating agents in gingelly.

Full text

Global Journal of Molecular Sciences 4 (2): 49-55, 2009
ISSN 1990-9241
© IDOSI Publications, 2009
Corresponding Author: Dr. R. Somasundaram, Stress Physiology Lab, Department of Botany,
Annamalai University, Annamalainagar 608 002, Tamilnadu, India
49
Induction of Drought Stress Tolerance by Paclobutrazol
and Abscisic Acid in Gingelly (Sesamum indicum L.)
R. Somasundaram, Cheruth Abdul Jaleel, M.M. Azooz,
1 1 2,3
Sindhu S. Abraham, M. Gomathinayagam and R. Panneerselvam
11 1
Stress Physiology Lab, Department of Botany,
1
Annamalai University, Annamalainagar 608 002, Tamilnadu, India
Department of Botany, Faculty of Science, South Valley University, 83523 Qena, Egypt
2
Department of Biology, Faculty of Science, King Faisal University,
3
P.O. Box: 380, Al-Hassa 31982, Saudi Arabia
Abstract: For the past several years, several techniques of physiology have been applied to overcome the water
deficit and drought stress in field crops. However little information is gained on the response to PBZ and
ABA treatments under drought stress and their ameliorative actions on Sesamum. So a study was carried out
to understand the effect of PBZ and ABA on drought stress amelioration in Sesamum indicum L. The main
aspects studied were the non-enzymatic antioxidant changes in different parts of treated, drought stressed as
well as control plants. The non-enzymatic antioxidants (ascorbic acid and tocopherol) were extracted and
estimated. The non-enzymatic antioxidant molecules like ascorbate and -tocopherol showed significant
increase under drought condition in Sesamum indicum. PBZ caused significant enhancement in these
antioxidant enzymes under drought stress and also in well-watered conditions. It is not so with ABA treatment.
ABA slightly reduced the non-enzymatic antioxidant contents. From the results, it can be concluded that, these
growth regulators are better suited as stress ameliorating agents in gingelly.
Key words: Non-enzymatic antioxidants Ascorbic acid Tocopherol Drought stress Sesamum indicum
INTRODUCTION physiological responses of plant to water deficits
Soil water availability represents a major water stress [6].
environmental constraint under Mediterranean Water stress is considered to be a moderate loss of
conditions and predictions suggest that the water, which leads to stomatal closure and limitation of
decline in total rainfall in the Mediterranean area will gas exchange. Desiccation is a much more extensive loss
be drastic. Under such conditions, it is likely that plants of water which can potentially lead to gross disruption of
will experience increasing water deficit stress in their metabolism and cell structure and eventually to the
natural communities [1-4]. Water stress tolerance is seen cessation of enzyme catalyzed reaction [7,8]. Water stress
in almost all plant species but its extent varies from is characterized by reduction of water content, turgor,
species to species [2-3]. A better understanding of the total water potential, wilting, closure of stomata and
physiological strategy adopted by a drought resistant decrease in cell enlargement and growth. Severe water
variety to cope with water deficit requires through study stress may result in arrest of photosynthesis, disturbance
of the relationship between water use efficiency and of metabolism and finally dying [6-9].
transpiration. In crops like wheat, the detrimental effects Tolerance to abiotic stresses is very complex,
of water deficits on the harvest index also minimizes the due to the complexity of interactions between stress
impact of the water limitation on crop productivity and factor and various molecular, biochemical and
increase the efficiency of water use [5]. The numerous physiological phenomena affecting plant growth and
generally vary with the severity as well as the duration of

Global J. Mol. Sci., 4 (2): 49-55, 2009
50
development [10-12]. High yield potential is the target of between 60-75 per cent. The experimental part of this
most crop breeding, not superior drought resistance and work was carried out in Botanical Garden and Stress
in many cases high yield potential can contribute to yield Physiology Lab, Department of Botany, Annamalai
in moderate stress environment [7-9]. University, Tamil Nadu. The methodologies adopted are
PBZ (2RS, 3RS)-1-(4-chlorophenyl)-4,4-dimethyl-2- described below.
(1H-1,2,4-trizol-1-yl)-pentan-3-ol] is a triazolic group of The plants were raised in Botanical Garden, during
fungicide which have PGR properties. The growth the months of February – May, 2006. The seeds were
regulating properties of PBZ are mediated by changes in surface sterilized with 0.2% Mercuric chloride solution for
the balance of important plant hormones including the five minutes with frequent shaking and thoroughly
Gibberellins, ABA and cytokinins [13-15]. The application washed with tap water. The experiments were carried out
of PBZ have no risk to human health and showed in polythene bags (27x16 cm). The pots were filled with
increased yield of crops. PBZ has been proved as an 3 kg uniform soil mixture containing red soil: sand: farm
agent in stress amelioration in medicinal plants [16-19]. yard manure (FYM) in 1:1:1 ratio. The experiment was laid
In spite of the plants growth regulating properties, out in a Completely Randomized Block Design (CRBD).
it is reported that PBZ have some negative side effects In the preliminary experiments, 2, 5, 10, 15 and
on soil microorganisms. Anyhow, there are reports on 20 mg L paclobutrazol and 5, 10 and 15 ìM ABA were
microorganisms, which are capable of PBZ degradation used for treatment to determine the optimum
on soil. concentration. Among the treatments, 5 mg L
Paclobutrazol has been proved as an agent in stress paclobutrazol and 10 ìM ABA concentration increased
amelioration in medicinal plants. Paclobutrazol increased the growth and dry weight significantly and higher
the diameter and length of fibrous roots and enhanced concentration slightly decreased the growth and dry
the lateral root formation [14-16]. Gingelly (Sesamum weight when compared to drought stressed plants. In the
indicum L.) is a member of the Pedaliaceae family. lower concentrations, there was no change in weight and
Gingelly is one of the ancient oil seed crop cultivated for growth. Hence 5 mg L paclobutrazol concentration was
its superior quality oil and seed, hence it is regarded as used to study the effect of paclobutrazol and 10 ìM ABA
“Queen of the oil seeds”. This species is native to Africa. on the drought stress amelioration of Sesamum indicum.
It is cultivated extensively in USA, India, Burma, Drought Treatment intervals were from 30 DAS 2, 4
Indo-china and Japan. India is the largest producer of and 6 days interval drought (DID). The treatments were
sesame in the world. Tamil Nadu is one of the major given as foliar spray for ABA and soil drenching for PBZ
sesame growing state in India. Sesame is used in on 32, 34 and 36 days after sowing (DAS).
traditional systems of medicine for curing many diseases. The plants were taken randomly on 33 (2 DID),
It has a good composition of amino acids, protein, niacin, 35 (4 DID) and 37 (6 DID) DAS and separated into roots,
folic acid, vitamin E, calcium and Phosphorus. stems and leaves and used for determining antioxidant
The objectives of the present study were to potentials.
understand the effect of paclobutrazol and ABA in
drought stress amelioration in Sesamum indicum L. Antioxidants
through their effects on the plant’s non-enzymatic Ascorbic Acid: Ascorbic acid content was assayed as
antioxidant potential under drought stress conditions. described by Omaye et al. [20].
MATERIALS AND METHODS Extraction: One gram of fresh material was ground in a
The seeds of Sesamum indicum L. were obtained was centrifuged at 3500 rpm for 20 minutes. The pellet was
from Department of Agronomy, Faculty of Agriculture, re-extracted twice with 10 percent TCA and supernatant
Annamalai University. The triazole compound was made to 10 ml and used for estimation.
paclobutrazol was obtained from Syngenta, India Ltd.,
Mumbai. ABA was purchased from Himedia India Ltd., Estimation: To 0.5 ml of extract, 1 ml of DTC reagent
Mumbai. (2,4-Dinitrophenyl hydrazine-Thiourea-CuSO reagent)
During the study, average temperature was 32/26°C was added and mixed thoroughly. The tubes were
(maximum/minimum) and relative humidity (RH) varied incubated at 37 °C for 3 hours and to this 0.75 ml of
-1
-1
-1
pestle and mortar with 5 ml of 10 per cent TCA, the extract
4

Root
0
20
40
60
80
100
120
140
160
180
2 DID 4 DID 6 DID
% over control
DD+PBZ D+ABA
PBZ ABA Stem
0
50
100
150
200
2 DID 4 DID 6 DID
% over control
DD+PBZ D+ABA
PBZ ABA
Leaf
0
20
40
60
80
100
120
140
160
180
2 D ID 4 D ID 6 D ID
% over control
D D+PBZ D+ABA
PBZ ABA
Global J. Mol. Sci., 4 (2): 49-55, 2009
51
Fig. 1: Individual and combined effects of drought, PBZ, ABA on ascorbic acid contents o f Sesamum indicum
ice cold 65 per cent H SO was added. The tubes at 520 nm. The -tocopherol content was calculated
24
were then allowed to stand at 30 °C for 30 minutes. The using a standard graph made with known amount of
resulting colour was read at 520 nm in spectrophotometer -tocopherol.
(U-2001-Hitachi). The ascorbic acid content was
determined using a-standard curve prepared with ascorbic Statistical Analysis: Each treatment was analysed with at
acid and the results were expressed in milligrams per gram least seven replicates and a standard deviation (SD) was
dry weight. calculated and data are expressed in mean ± SD of seven
-Tocopherol: -Tocopherol activity was assayed as
described by Backer et al. [21]. Ascorbic Acid (Fig. 1)
Extraction: Five hundred milligrams of fresh tissue was with age in paclobutrazol treated, drought stressed and
homogenized with 10 ml of a mixture of petroleum ether control plants. ABA decreased the ascorbic acid content
and ethanol (2:1.6 v/v) and the extract was centrifuged at in roots at all stages of growth and it was 60.99 per cent
10,000 rpm for 20 minutes and the supernatant was used and 28.96 per cent over control in well watered and
for estimation of -tocopherol. stressed respectively on 6 DID.
Estimation: To one ml of extract, 0.2 ml of 2 per cent Stem: The ascorbic acid content of the stem of Sesamum
2,2-dipyridyl in ethanol was added and mixed thoroughly indicum increased with age in the treated and control
and kept in dark for 5 minutes. The resulting red colour plants. Paclobutrazol and drought treatments increased
was diluted with 4 ml of distilled water and mixed well. the ascorbic acid content in the stem at all stages of
The resulting colour in the aqueous layer was measured growth and it was 114.76 per cent and 99.15 per cent over
replicates. RESULTS
Root: In the roots the ascorbic acid content was increased

Root
0
50
100
150
200
250
300
350
2 DID 4 DID 6 DID
% over control
DD+PBZ D+ABA
PBZ ABA
Stem
0
50
100
150
200
250
300
350
2 DID 4 DID 6 DID
% over control
DD+PBZ D+ABA
PBZ ABA
Leaf
0
100
200
300
400
2 D ID 4 D ID 6 D ID
% over control
DD+PBZ D+ABA
PBZ ABA
Global J. Mol. Sci., 4 (2): 49-55, 2009
52
Fig. 2: Individual and combined effects of drought, PBZ, ABA on a-tocopherol contents o f Sesamum indicum
control respectively on 6 DID. ABA resulted a significant Stem: The -tocopherol content of the stem of Sesamum
reduction (56.16 per cent over control) in ascorbic acid indicum increased with age in the treated and control
content in stem of Sesamum indicum at 6 DID. plants. Paclobutrazol and drought treatments increased
Leaf: The ascorbic acid content of the leaves of growth and it was 174.40 per cent and 309.02 per cent over
Sesamum indicum increased with age in the treated control respectively on 6 DID. ABA resulted a significant
and control plants. Paclobutrazol and drought reduction in -tocopherol content in stem of Sesamum
treatments increased the ascorbic acid content in the indicum at all sampling days.
leaves at all stages of growth and it was 107.62 per cent
and 93.38 per cent over control respectively on 6 DID. Leaf: In the leaves the -tocopherol content was
ABA resulted a significant reduction in ascorbic acid increased with age in paclobutrazol treated, drought
content in leaves of Sesamum indicum at all stressed and control plants. ABA decreased the
sampling days. -tocopherol content in leaves at all stages of growth and
-Tocopherol (Fig. 2) well watered and stressed respectively on 6 DID.
Root: -tocopherol of the drought stressed plant
roots significantly increased when compared to DISCUSSION
control plants. The extent of increase was 339.4 per
cent over control on 6 DID. Paclobutrazol caused Ascorbic Acid: The ascorbic acid content was increased
an enhancement in -tocopherol content of roots with age in paclobutrazol treated drought stressed and
under drought as well as well-watered conditions. ABA control plants. ABA decreased the ascorbic acid content
was an inhibitor of -tocopherol individually and also in roots at all stages of growth. Ascorbate is one of the
under drought stress. most extensively studied anti-oxidant and has been
the -tocopherol content in the stem at all stages of
it was 78.35 per cent and 150.31 per cent over control in

Global J. Mol. Sci., 4 (2): 49-55, 2009
53
detected in the majority of plant cell types, organelles 2. Sankar, B., C. Abdul Jaleel, P. Manivannan,
and apoplast [1,22]. Water stress resulted in significant
increases in antioxidant AA concentration in
Catharanthus roseus [23].
Triazole increased the level of antioxidants like
ascorbic acid and -tocopherol like in Withania somnifera
Dunal. seedlings and protected membrane by preventing
or reducing oxidative damage [24]. Increase in ascorbic
acid content was reported in the triadimefon treated
Catharanthus roseus [25] and Withania somnifera [26].
A decrease in ascorbic acid was reported in ABA
treatment in Ocimum sanctum plants [27].
- Tocopherol: -tocopherol of the drought stressed
plants significantly increased when compared to
control plants. Paclobutrazol caused an enhancement
in -tocopherol content of roots under drought as well
as well-watered conditions. ABA was an inhibitor of
-tocopherol individually and also under drought stress.
The active oxygen species formed at the membrane of
leaves under drought stress was efficiently removed
upon rehydration with increase in the -tocopherol and
-carotene [28-30]. Soil applied propiconazole alleviated
the impact of salinity on Catharanthus roseus by
improving antioxidant status especially -tocopherol [31].
Alterations in biochemicals including non-enzymatic
antioxidants in white yam (Dioscorea rotundata Poir.)
under triazole fungicides application was previously
reported [32].
CONCLUSION
The non-enzymatic antioxidant molecules like
ascorbate and -tocopherol showed significant increase
under drought condition in Sesamum indicum. PBZ
caused significant enhancement in these antioxidant
enzymes under drought stress and also in well-watered
conditions. It is not so with ABA treatment. ABA slightly
reduced the non-enzymatic antioxidant contents. From the
results, it can be concluded that, these growth regulators
are better suited as stress ameliorating agents in gingelly.
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