Assessment of Salicylic Acid and Trehalose Impact on Root Growth and Water Relations in Relation to Grain Yield of Droughted Wheat Cultivars
Heshmat S Aldesuquy1*, Farag L Ibraheem1, Hanan E Ghanem1
1Faculty of Science, Mansoura University, Egypt
2Department of Plant Molecular Biology, Umm-AlQura University, Saudi Arabia
Submission: April 10, 2018;Published: June 26, 2018
*Corresponding author: Heshmat S Aldesuquy, Faculty of Science, Department of Botany, Mansoura University, Egypt,
How to cite this article: Heshmat S A, Farag L I Hanan E G. Assessment of Salicylic Acid and Trehalose Impact on Root Growth and Water Relations in Relation to Grain Yield of Droughted Wheat Cultivars. Nutri Food Sci Int J. 2018; 7(1): 555701. DOI:10.19080/NFSIJ.2018.07.555701.
Drought stress is a major constraint for crop production in arid and semiarid regions. In this study, plant water status could be considered as one of the most critical criteria not only determining but also controlling the overall plant performance. Water stress greatly decreased root biomass, root density and distribution. On the contrary, root length, number of adventitious roots as well as root/shoot ratio was found to increase as a result of drought stress. The inhibition of plant growth under water stress conditions was intensively proved to be associated with altered plant-water relations. Based on our results, we conclude that the drought exposure imposed evident on root growth as well as plant water-relations. On the other hand, the exogenous application of salicylic acid (SA), trehalose (Tre) or their interaction appeared to mitigate this damage effect of drought with different magnitude throughout counteracting the negative effects of water stress on all growth criteria of root and improving leaf turgidity by decreasing the rate of transpiration, increasing relative water content and decreasing saturation water deficit as well as increasing water use efficiency for economic yield. Grain yield was positively correlated with root fresh mass, root dry mass, root density and root distribution. On the other hand, the grain yield was negatively correlated with root length, root/shoot ratio and the number of adventitious roots of both droughted wheat cultivars. Furthermore, Grain yield positively correlated with transpiration rate, RWC, WUEG, WUEB, osmotic pressure, total soluble sugars, proline, keto acids, citric acid and negatively correlated with SWD, total soluble nitrogen as well as Na+ and Cl-.
Keywords: Wheat; Drought; Root growth; Water use efficiency; Transpiration; Relative water content; Saturation water deficit
Abbreviations: RWC: Relative Water Content; SA: Salicylic Acid; SWD: Saturation Water Deficit; Tre: Trehalose; WUE: Water Use Efficiency
Stress could lead to marked changes in the growth, morphology and physiology of roots, which would in turn change water and ion uptake; the whole plant is then affected when its root grows in unfavorable medium with less water availability . In this connection, it is well documented that there is marked reduction in root growth rate under water deficit conditions, indicating that this effect is entirely due to the change in plant-water relations . Assessment of root density and distribution could be considered as a key factor for water and nutrient uptake by a plant in soil .
Generally, drought is one of the most common stressful conditions that plants experience in their environment, where it has a negative effect on plant-water relations . Transpiration can be regarded as the dominant process in plant-water relations. Many plants limit transpiration by stomatal closure at low negative water potentials originated during the drought period . In this respect, transpiration rate in common bean plants were reported to decrease after four days of withholding water . Similarly, drought induced marked decrease in diurnal and mean daily values of transpiration rate in two wheat cultivars .
The pattern of water use is crucial for plants grown with a limited amount of water in soil profile because the plant success depends largely on a sustained water use [7,8]. However, plants are developmentally and physiologically designed by evolution to reduce water use under drought stress . Therefore, the study of water use efficiency (WUE), defined as the ratio of dry matter production to water use, is particularly interesting in situations where growth is affected as a result of limiting water availability . The effect of drought on WUE has been investigated in different plant species such as Zea mays .
The inhibition of plant growth under water stress conditions is associated with altered water relations . Hence, less absorbed water means less water content indicated by relative water content (RWC), saturation water deficit (SWD), degree of succulence and degree of sclerophylly .
Leaf relative water content (RWC) is proposed as a more
important indicator of water status than other water potential
parameters under drought conditions, as it is believed that
RWC is a reliable parameter for quantifying the plant-drought
response . During plant development, water deficiency
significantly reduces RWC . A decrease in RWC in response
to water deficit had been reported in several studies [16,17]. As
a practical proof, Shinde observed that drought considerably
reduced RWC in four groundnut varieties. Additionally, waterstressed
wheat and rice plants had lower relative water content
than non-stressed ones .
Yield is a result of the integration of metabolic reactions in
plants; consequently any factor that influences this metabolic
activity at any period of plant growth can affect the yield
. Crop plants are especially sensitive to drought stress
during the early reproductive stage, which causes significant
yield loss in cereal production and detrimental effects on
grain quality. The present study was undertaken to examine
the effect of water stress on growth vigor of root as well as
osmotic adjustment and solutes allocation in wheat flag leaf of
Gemmieza-7 (drought sensitive cultivar) and Sahel-1 (drought
tolerant cultivar) during grain filling.
Pure strains of Triticum aestivum L. Gemmieza-7 (drought
sensitive cultivar) and Sahel-1 (drought tolerant cultivar) were
kindly supplied by the Agricultural Research Center, Ministry
of Agriculture, Giza, Egypt.
For soaking experiment, a homogenous lot of Triticum
aestivum L. (i.e. either sensitive or tolerant cultivar) grains
were selected. The grains were separately surface sterilized
by soaking in 0.01M HgCl2 solution for three minutes, then
washed thoroughly with distilled water. The sterilized grains
from each cultivar were divided into two sets (≈ 500g per set
for each cultivar). Grains of the 1st set were soaked in distilled
water to serve as control, while those of the 2nd were soaked
in salicylic acid (3mM) for about 6 hours.
After soaking, thoroughly washed grains were drilled in 20
November 2011 and 2012 in plastic pots (20cm in diameter)
filled with 5.5kg soil (clay/sand 2/1, v/v), where fifteen grains
was sown in each pot. The pots were then kept in a greenhouse
at Botany Department, Faculty of Science, Mansoura
University, Egypt. The plants were subjected to natural day/
night conditions (minimum/maximum air temperature and
relative humidity were 15/25 C and 35/45%; respectively) at
mid-day during the experimental period. The plants in all sets
were irrigated to field capacity by tap water.
After two weeks from sowing, thinning was started so that
five uniform seedlings were left in each pot for the subsequent
studies. On the day 65 after planting (at the beginning of
heading) the pots of the 1st set was allocated to four groups (20
pots per each group) as follows: control (cont.), water stress
(WS), trehalose control, trehalose + water stress (trehalose
+ WS). The 2nd set group was allocated to four groups as
follows: salicylic acid control (SA), salicylic acid + water stress
(SA+WS), control trehalose + salicylic acid (SA + trehalose) and
salicylic acid + trehalose + water stress (SA+ trehalose +WS).
For trehalose (1.5mM) treatment, the plants were sprayed by
trehalose 48hrs before starting the stress period and weekly
during the stress period.
Water deficit was imposed by withholding water at the
reproductive stage for 30days within two periods: on the
day 65 from planting (heading stage) and at the day 80 from
planting (anthesis stage). Each droughted pot received 500ml
water at the end of 1st stress period. At the end of stress
periods, re-watering to the field capacity was carried out.
The undroughted (control) plants were irrigated to the field
capacity during the stress period, and all plants were left to
grow until grain maturation under normal irrigation with tap
water. After thinning and at heading, the plants received 36kg
N ha-1 as urea and 25kg P ha-1 as super-phosphate. Samples
from flag leaves were taken from each treatment during grainfilling
(21 days post-anthesis) (i.e. 106 days after sowing).
To estimate the morphological features of wheat roots
grown under different growth conditions, ten replicates
from root system of each treatment were harvested. For the
root system, root biomass, root length and the number of
adventitious roots were estimated.
For measuring transpiration rate, the method of Kanemasu
et al.  was followed. Before starting transpiration
measurement, the soil surfaces in the pots were covered
by the projecting margins of the plastic bags lining the
pots and wrapping then around the base of stems. This act
prevents water loss by direct evaporation from the soil and
any measurable loss, hence, represents loss by transpiration.
Each pot was weighed periodically during daytime. This was
carried out at 3hours intervals, namely at 7am, 10am, 1pm,
4pm and 7pm for one day and the plants were then harvested
by cutting just above the soil surface. Fresh weight of leaves
was recorded for each pot. Transpiration was expressed in
"mg water/g leaf fresh weight/hour". Transpiration rate was
calculated for the four daily periods. Actual and saturation
vapour pressures (mmHg) at the ambient temperatures were
obtained from hygrometric tables and vapour pressure deficit
(VPD) was calculated.
Water use efficiency was calculated by dividing the grain
yield (ton ha-1) or the biomass yield (ton ha-1) by the total amount
of water added (gallon). Therefore, water use efficiency for
grain yield (WUEG) was calculated from grain yield and water
use efficiency for biomass yield (WUEB) was estimated from
biomass yield according to Stanhill  as following:
WUEG = Grain yield (ton) / Total water used (gallon)
WUEB = Biomass yield (ton) / Total water used (gallon)
For measuring relative water content (RWC), the method
of Weatherly  and its modification by Weatherly & Barrs
 was adopted. Leaf discs were punched from the centre
of the leaf. They were weighed to estimate their fresh mass
(FM), floated for 4 hours on distilled water and weighed
again to estimate their turgid mass (TM). For dry mass (DM)
determination, the discs were oven-dried at 80ºC till constant
weight. Relative water content was calculated as:
It should be mentioned that the sample numbers which
were taken for investigation were as follows: ten for growth
parameters, ten for agronomic traits and three for all chemical
analyses and only the mean values were represented in the
respective figures and tables. The data were subjected to
one-way analysis of variance (ANOVA), and different letters
indicate significant differences between treatments at p ≤
0.05, according to CoHort/ CoStat software, Version 6.311.
As compared to the control values, water stress led
to marked decrease (p ≤ 0.05) in root biomass (fresh and
dry masses), root density and distribution of both wheat
cultivars during grain-filling. On the other hand, water stress
induced noticeable increase (p ≤ 0.05) in the root length (nonsignificant
increase in case of sensitive cultivar), root/shoot
ratio and number of adventitious roots of both wheat cultivars
during grain-filling. The magnitude of reduction was greater
in drought sensitive cultivar than drought tolerant one. In
the majority of cases, application of SA and/or Tre induced
a marked increase (p ≤ 0.05) in the values of root biomass
(fresh and dry masses), root length (non-significant increase
in case of sensitive cultivar) also number of adventitious as
well as root/shoot ratio, root density and distribution of both
wheat cultivars. However, interaction of SA and Tre was the
most effective treatment in increasing all growth vigor of root
Data are represented as means± standard errors from 10 replicates. Different letters within the same column indicate significant differences between treatments at p ≤ 0.05, according to CoHort/ CoStat software, Version 6.311.
Soil moisture content was markedly reduced at the end
of the stress period, and it was found to be about 23.3 and
4.6 % (% of oven soil dry weight) for control and droughted
pots respectively. Transpiration rate and concurrent effective
climatic parameters are shown in Figure 1 & 2. Transpiration
rate generally followed the fluctuations in temperature, while
it was inversely proportional to relative humidity of air.
Transpiration rate in wheat plants and concurrent effective
climatic parameters were measured on one day, along with
other water relations (relative water content and saturation
water deficit). In general, the maximum transpiration rate
was attained in the period of mid-day (at 10-1pm) in control
and differently treated plants. Water stress caused marked
reduction (p ≤ 0.05) in diurnal values of transpiration all over
the daytime, and also in the mean daily value of transpiration
rate. The application of SA and/or Tre induced significant
decrease (p ≤ 0.05) in transpiration rate of water stressed
and unstressed wheat plants. Furthermore, the magnitude of
decrease in transpiration rate depends mainly on the daytime
and on the chemical used. It was clear that grain pre-soaking
in SA was more effective than the foliar application of Tre
in decreasing the transpiration rate. Moreover, SA and Tre
interaction treatment was the more effective treatment than
SA or Tre alone especially in the water-stressed plants.
It is obvious from the results in Figure 3 that the values of
water use efficiency for grain (WUEG) and for biomass (WUEB)
in the stressed plants were significantly lower (p ≤ 0.05)
than those of control plants. Comparing both cultivars, the
highest WUEG and WUEB values were observed in Sahel-1than
Gemmieza-7 under water stress conditions. Application of SA
and/or Tre clearly improved WUEG and WUEB in both stressed
and unstressed wheat plants. In addition, the treatment with
SA and Tre recorded the highest WUEG and WUEB values than
the other treatments.
As compared to control plants, water stress caused
additional reduction (p ≤ 0.05) in RWC % of wheat flag leaf
during grain filling in both cultivars with more reduction in
drought sensitive cultivar in comparing to drought tolerant
one. Furthermore, the application SA and/or Tre alleviated the
deleterious effects of water stress by improving leaf turgidity,
where each of these treatments caused significant increase
(p ≤ 0.05) in the mean daily values of RWC if compared with
stressed plants. This effect was more pronounced with the
interaction of SA and Tre interaction (Figure 4 & 5).
The data in Figure 6 & 7 showed that, water stress increased
significantly (p ≤ 0.05) SWD % in flag leaf of both cultivars
during grain filling. Comparing both cultivars higher SWD%
was observed in drought sensitive cultivar than the drought
tolerant one under water stress conditions. Application of SA
and/or Tre interaction caused significant decrease (p ≤ 0.05)
in SWD as compared with water-stressed plants. SA or SA and
Tre interaction was the most effective in decreasing the values
of SWD in flag leaf of wheat plants.
The data in Figure 8 revealed that water stress caused
significant reduction (p ≤ 0.05) in grain yield of wheat plants.
With regard to the wheat cultivar, the sensitive one was more
affected by water stress than the tolerant one. SA and/or Tre
induced additional increase (p ≤ 0.05) in grain yield of stressed
wheat plants. Moreover, the treatment of SA and Tre improved
grain yield more than that of SA or Tre only.
Plant species and cultivars have different physiological
mechanisms in response to drought stress . The use of
morpho-physiological and biochemical criteria has been
recommended to achieve a rapid and simple screening
of highly drought-tolerant individuals. In order to define
drought tolerance or sensitivity of both cultivars, growth
parameters like lengths, dry and fresh weights of roots were
tested under the effect of water-stress during grain-filling.
Various environmental stresses that could result in both
general and specific effects on their growth and development.
Morphological characteristics were shown to be an important
factor in controlling the yield of crop plants .
The current results showed that drought generally caused
a noticeable reduction in almost all growth criteria of root of both wheat cultivars Gemmieza-7 (drought sensitive) and
Sahel-1 (drought tolerant) during grain-filling. Extent of
reduction was more obvious particularly in Gemmieza-7. These
results were in accord with those obtained by Gomaa et al. 
who postulated that stress-induced inhibition of plant growth
as a whole may be due to the elevation in osmotic pressure,
which may disturb most cellular physiological and metabolic
The inhibitory effect of water stress was more pronounced
in the sensitive cultivar than in the tolerant one. The variation
in response of wheat cultivar for drought stress tolerance was
known in many studies [28,29]. In this respect Sankar et al.
 have reported that the root length, shoot length, total leaf
area, fresh weight and dry weight of bhendi are significantly
reduced under drought stress treatment. In the present study,
water stress greatly decreased root biomass, root density
and distribution. On the contrary, root length, number of
adventitious roots as well as root to shoot ratio was found to
increase as a result of drought stress. In agreement with these
results, stressing mulberry plants generally decreased root
growth parameters as revealed by Das et al. .
Stress could lead to marked changes in the growth,
morphology and physiology of roots, which would in turn
change water and ion uptake; the whole plant is then affected
when its root grows in unfavorable medium with less water
availability . In this connection, it is well documented that
there is marked reduction in root growth rate under water
deficit conditions, indicating that this effect is entirely due to
the change in plant-water relations .
Morphological characters like fresh and dry masses have a
profound effect in water-limited conditions . In the present
investigation, both fresh and dry masses of wheat roots were
significantly decreased in response to drought. These results
appeared to match those obtained by Younis et al.  who
noticed that root biomass of Vigna sinensis and Zea mays plants
was suppressed under stress. Also, Khodary  reported
that stressing Zea mays plants reduced root fresh and dry
masses. The reduction in root biomass can be attributed to the
inhibitory effect of stress-induced ABA on cell division and/or
cell expansion .
The results of the present study also revealed that stress
conditions could induce root length and the number of
adventitious roots as compared with the unstressed plants .
Continuation of root growth under drought stress through
stimulation in root length and number of adventitious roots
is an adaptive mechanism that facilitates water uptake from
deeper soil layers. These results are in accordance with those
obtained by Sundaravalli et al.  & Yin et al. . Plants
must develop vigorous root system that allows them to grow
and overcome any stress conditions. Moreover, a large root
system may improve a plant’s competitive ability for water
during drought stress, which is a plant’s individual survival
strategy in natural selection. According to life-history strategy
theory, plants with a large root system are partitioning more
photosynthetic products to roots, which imply a reduced
partition to reproductive growth.
Assessment of root density and distribution could be
considered as a key factor for water and nutrient uptake
by a plant in soil . In this investigation, stress resulted in
significant decrease in both root density and distribution of
wheat plants. Root density relates dry mass production to the
unit root length, while root distribution represents the fresh
mass accumulated per the unit root length.
Stressing wheat plants significantly increased root/shoot
ratio when compared with the control plants. This finding
coincided with that of many other researchers [13,38]. In this
respect, Jabeen et al.  suggested that the increase in root/
shoot ratio under water stress conditions may be due to:
(i) The increased accumulation of assimilates diverted
to root growth.
(ii) Differential sensitivities of root and shoot to
endogenous ABA and/or (iii) greater osmotic adjustment in
roots compared with shoots. Matching these assumptions,
El-Hendawy  assumed that although stress can induce
rapid reduction in root growth, shoot growth decreases
proportionally more than root growth, causing an increase
in the root/shoot ratio.
Drought affects plant water relations, reduces water
contents of leaf and plant, causes osmotic stress, inhibits cell
expansion and cell division as well as growth of plants as a
whole . Determination of water relations is critical for
any study of plant resistance to water stress . Plant water
status is important not only for plant growth under favorable
environmental conditions but also for their ability to tolerate
water deficit . Additionally, the importance of the internal
water balance in plant water relations is generally accepted
because of the close relationship between the balance and
turgidity to the rates of physiological processes that control
the quality and quantity of growth . Among the common
plant-water relations, diurnal changes and mean daily values of
relative water content (RWC), saturation water deficit (SWD)
and transpiration rate were extensively studied. In addition,
water use efficiency (WUE) is of special importance to plant
water status particularly under water deficit circumstances. A
favorable water balance under water deficit conditions can be
achieved either by conserving water, restricting transpiration
or by accelerating water uptake.
The results of the present investigation clearly elucidated
that stress caused marked reduction in the diurnal and mean
daily values of transpiration rate allover the daytime in two
wheat cultivars during grains filling. These results were in
conformity with those obtained by Trapp et al.  pointed
out that less water supply could strongly inhibit transpiration.
The decline in transpiration rate in response to water
deficit is widely reported in literatures  and the effect is
more pronounced in susceptible genotypes than in tolerant
T he a pplication o f S A a nd/or T re i nduced s ignificant
decrease in transpiration rate of water stressed and unstressed
wheat plants. Furthermore, the magnitude of decrease in
transpiration rate depends mainly on the daytime and on the
chemical used. It was clear that grain pre-soaking in SA was
more effective than the foliar application of Tre in decreasing
the transpiration rate. Moreover, SA and Tre interaction
treatment was the more effective treatment than SA or Tre
alone especially in the water-stressed plants. These results
are in good agreement with those obtained by Aldesuquy et al.
 studied the effect of antitranspirants (sodium salicylate
or ABA) and salinity on some water relations of wheat plants.
They found that sodium salicylate or ABA appeared to regain
the leaf turgidity of saline-treated plants by inducing additional
decreases in transpiration rates and therefore improved the
water use efficiency.
Water use efficiency (WUE) is the ratio of dry matter
production to water use . Increasing WUE of plants is
vital especially to achieve optimum growth with optimal
water supply . In this study, droughted wheat plants
exhibited lower water use efficiency for grain WUEG and
biomass WUEB compared with their unstressed relatives.
Comparing both cultivars, higher WUEG and WUEB values
were observed in Sahe-1 than Gemmieza-7 under water stress
conditions. Water use e fficiency (WUE) has given much
attention as a physiological trait related to plant drought
resistance. Molecular research regarding WUE enhancement
is playing crucial role in selection and cultivation of droughttolerant.
When breeding for drought tolerance, biomass
productivity and WUE are considered fundamental agronomic
Application of SA and/or Tre clearly improved WUEG
and WUEB in both stressed and unstressed wheat plants. In
addition, the treatment with SA and Tre recorded the highest
WUEG and WUEB values than the other treatments.
Leaf relative water content (RWC) has been emphasized
as a better indicator of water status of a plant than water
potential . The results revealed that drought resulted in
noticeable reduction in the mean daily values of RWC with a
concomitant increase in SWD of wheat leaves during grain
filling in both cultivars. The decrease in RWC is more obvious
in drought sensitive cultivar than the drought tolerant one.
The suppression of leaf RWC under stress implies that there is
a reduction in turgor and that the plant suffers from restricted
water availability to the cells . This decrease in turgor under
less water availability could conceivably reduce the expansive
growth of cells . In this context, marked reduction in RWC
of different plant species under water stress conditions was
reported in other studies [50,51].
In the present study, the observed reduction in RWC in
close parallelism with the increase in SWD. Furthermore, the
application SA and/or Tre alleviated the deleterious effects of
water stress by increasing leaf turgidity, where each of these
treatments caused significant increase in the mean daily values
of RWC and significant decrease in the mean daily values of
SWD if compared with stressed plants. This effect was more
pronounced with the interaction of SA and Tre interaction.
These results were similar to those obtained by Aldesuquy et
al.  using wheat plants grown under salinity conditions
and treated with antitranspirants (sodium salicylate or ABA).
Also, Kumar et al.  reported maintenance of water balance
with foliar application of salicylic acid.
Alam et al.  reported that combination of Tre with
drought showed improved leaf relative water content (RWC) in
Brassica species. Similar findings were documented previously
by Tre addition with abiotic stress [54,55].
Water stress reduced grain yiled in both wheat cultivars.
Crop plants are especially sensitive to drought stress during
the early reproductive stage, which causes significant yield
loss in cereal production and detrimental effects on grain
quality. This is a well established fact that yield of crop plants
in drying soil reduces even in tolerant lines of that crop species
[32,56]. Drought stress during the early stage of reproductive
growth tends to reduce yield by reducing seed number. During
seed development stress reduces yield by reducing seed
size. Prolonged moisture stress during reproductive growth
can severely reduce yield because of reduced seed number
and seed size . The yield components, like grain yield,
grain number, grain size, and floret number, are decreased
under drought stress treatment in sunflower . Moreover,
Amin et al.  attributed the increase in yield and yield
characteristics of onion plants with foliar spray of salicylic
acid to an increase in photosynthesis and assimilation and
translocation of assimilates, and greater nutrient uptake and
increased cytoplasmic streaming and cell integrity. In addition,
the promoting effect of SA on the flag leaf blade area and blades
area/plant of barley mentioned that enhancing effect of SA
on the availability and movement of nutrients could result in
stimulating different nutrients in the leaves and consequently
promote yield and yield components [59,60].
For growth criteria of root, the grain yield was positively
correlated with root fresh mass (r = 0.93, 0.97), root dry mass (r
= 0.89,0.95),root density (r = 0.86,0.83)and root distribution(r
= 0.93, 0.91). On the other hand, the grain yield was negatively
correlated with root length (r = -0.62, -0.39), root/shoot
ratio (r = -0.68,-0.56) and the number of adventitious roots (r
=-0.66, -0.31) of both droughted wheat cultivars respectively.
Furthermore, the grain yield was positively correlated with transpiration rate (r= 0.39, 0.06), RWC (r=0.89, 0.86), WUEG
(r= 1.00, 0.94), WUEB (r = 1.00, 1.00), conversely, a negative
correlation was recorded for SWD (r = - 0.89, - 0.86).
The applied chemicals appeared to mitigate the negative
effect of water stress on growth vigor of root and waterrelations
as well as grain yield of both wheat cultivars especially
the sensitive one. The effect was more pronounced with SA
and Tre treatment. This improvement would result from the
promotive effect of the provided chemicals on root growth
and recovery of leaf turgidity under water deficit condition.
Moreover, key players involved in SA and Tre-induced drought
tolerance needs to be clarified using proteomic and genomic