Vol.2, No.3, 159-166 (2011)
Copyright © 2011 SciRes. Openly accessible at http://www.scirp.org/journal/AS/
Agricultural Scienc es
Response of coleoptiles to water deficit: growth, turgor
maintenance and osmotic adjustment in barley plants
(Hordeum vulgare L.)
Águeda González1*, Luís Ayerbe2
1Departamento de Investigación Agroambiental, Alcalá de Henares, Spain; *Corresponding Author: agueda.gonzalez@madrid.org
2Centro de Recursos Fitogenéticos, Alcalá de Henares, Spain.
Received 11 January 2011; revised 23 May 2011; accepted 25 July 2011.
Cereal crop improvement programmes involve
the analysis of a great number of lines every
year; the availability of a simple, rapid method
that would allow the identification of a trait in
the early stages of plant development would
facilitate the selection process. This work re-
ports two experiments involving the germina-
tion of seeds in Petri dishes, perform ed to study
the effect o f water de ficit on the gro wth of barley
coleoptiles. In one experiment water stress was
induced by allowing evaporation from the Petri
dishes; in the other water stress was achieved
by adding pol yethy lene glycol 6000.
The growth of the control coleoptiles was
greater than that of the treatment coleoptiles in
all cases, but with differences between the dif-
ferent genotypes. A significant correlation (P <
0.01) was found between the relative growth of
the coleoptiles and turgor maintenance in the
seedlings. Significant correlations were also
seen between the relative growth of the coleop-
tiles and the osmotic adjustment of the flag leaf
(P < 0.05) and the grain weight (P < 0.01) in adult
plants. The genotypes that showed the greatest
relative growth also showed the greatest ca-
pacity for osmotic adjustment in the flag leaf
and produce d the grea te st y ie lds in e xperimen ts
with adult plants. The results indicate that the
growth of coleoptiles subjected to water deficit
could be used as a selection criterion in breed-
ing programmes designed to improve the tol-
erance of barley to drought.
Keywords: Barley; Drought Tolerance;
Water Potential; Osmotic Potential; Grain Yield
Obtaining high, stable yields is a priority aim of cereal
improvement programmes. In environments affected by
drought the improvement of yield is difficult given the
low heritability of this trait and because of the variable
quantity and temporal distribution of soil water. The use
of secondary traits, including physiological traits [1], has
been proposed as a possible solution to this problem. In
this approach the identification of traits that contribute
towards drought tolerance and that can be used as selec-
tion criteria in improvement programmes is essential for
increasing selection efficiency, especially in climates in
which water availability is low.
Unfortunately, the majority of physiological traits as-
sociated with drought tolerance that could be used as
selection criteria are not easy to measure, and physio-
logical screening tests are complex and slow when a
large number of genotypes are involved. These problems
can be minimised, however, if traits of interest can be
measured in the first stages of development with plants
growing in controlled environments as long as these
measures are sufficiently closely correlated with drought
tolerance at crop level. Under such conditions the selec-
tion process can be much more quickly and efficiently
undertaken—many genotypes can be studied at once and
the time and space required for tests to be performed are
reduced. Coleoptile length has been identified as one
interesting trait for improving drought tolerance. Final
coleoptile length is under the control of many genes and
regulated by environment. The expression of these genes
is differentially affected by the drought stress applied [2].
Heat-stress was associated with a decrease in the rate of
growth and in the final length of barley and wheat col-
eoptiles [3,4]
Osmotic adjustment is becoming increasingly recog-
nised as an efficient drought tolerance mechanism in
cultivated plants [5,6], exerting a positive effecteither
Á. González et al. / Agricultural Science 2 (2011) 159-166
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directly or indirectly—on the productivity of plants that
grow under drought conditions [7]. Genotypes with the
ability to make osmotic adjustments produce greater
yields; for example in chickpea [8,9], pea [10], sorghum
[11,12], wheat [13,14], barley [15,16], sunflower [17]
and potato [18] .
Osmotic adjustment consists in the active accumula-
tion of solutes in cells as a response to a reduction in the
water potential. This leads to cells retaining water and a
consequent tendency to retain their turgor pressure under
water deficit. Osmotic adjustment reduces the sensitivity
of processes dependent on turgor, such as growth and
stomatal activity, when the water potential falls [19].
Genetic variation is essential for a trait to be used as a
selection criterion in improvement programmes. The
existence of intraspecific variability with respect to os-
motic adjustment [6,16,17,19,20-22] and coleoptile growth
[23,24] has been demonstrated in different crops. This,
along with the possibility of identifying QTLs that con-
trol drought tolerance in seedling [25], and coleoptile
growth [26], renders the study of coleoptile growth of
great interest in the improvement of drought tolerance.
Differences in osmotic adjustment capacity can be
measured in adult plants. However, it is not easy to
measure in the very great numbers of lines that a breed-
ing programme handles every year. The aims of the pre-
sent work were to: 1) understand the response of differ-
ent barley genotypes to water deficit in their first weeks
of growth, 2) to determine whether any differences exist
in the growth of coleoptiles of different barley genotypes
under water deficit conditions, and 3) to study the rela-
tionship between osmotic adjustment of the coleoptiles
and that of adult plants.
2.1. Plant Materials and Stress Treatments
Eight barely genotypes were used in the present work,
including three improvement lines from ICARDA (L31,
L40 and L47) and five commercial varieties (Tipper,
Plaisant, Viva, Reinette and Albacete). Experiments to
determine the relationship between osmotic adjustment
and growth were performed in a germination chamber
following the method of Morgan [26]. Fourteen seeds
were placed on germination paper in 13 cm-diameter
Petri dishes, with six dishes per genotype (three control
dishes and three treatment dishes); 22 ml of distilled
water were then added to all the dishes. These dishes
were then placed in a germination chamber at a constant
temperature of 25˚C - 26˚C. After three days the lengths
of the coleoptiles in every dish were measured.
Two water deficit experiments were conducted. In the
first, water deficit was induced by allowing the evapora-
tion of the water from the Petri dish. After measuring the
length of the coleoptiles (initial length), the Petri dish
lids were left off. In the control dishes the germination
paper was placed over four 1 cm-tall methacrylate sup-
ports, and water added beneath the paper to help main-
tain the moisture level. These control dishes were then
placed once again in the germination chamber for 48 h at
26˚C and at 90% relative humidity (RH). The germina-
tion paper was mounted in the same fashion in the
treatment dishes, but these received no extra water.
These plates were then placed in a germination chamber
for 48 h at 26˚C and at 70% RH. The lengths of the col-
eoptiles of both the treatment and control plants were
then measured once more (final length).
In the second experiment, water deficit was induced
by the addition of PEG (PEG-6000). Twenty millilitres
of distilled water were added to each of the control
dishes, while 20 ml of PEG (30% p/v) were added to the
treatment dishes. All these plates were then introduced
into a germination chamber for 48 h at 26˚C before mea-
suring the coleoptiles again.
Relative growth was calculated as follows: (final
length - initial length)/initial length.
2.2. Measurements of Physiological
The stress suffered by the plants was determined by
measuring the water potential (
) and osmotic potential
s) using two coleoptiles from each dish. When the
final length was obtained, they were placed in hygrome-
try chambers following the same procedure employed
with adult plants [16]. Rectangular sections of the col-
eoptiles (5.7 cm2) were placed inside separate psy-
chrometer chambers. The closed chambers were allowed
to equilibrate in a water bath at 25˚C for 3 h. Measure-
ments of of the tissue were then made using a ther-
mocouple hygrometer (Wescor model C-52, Logan, UT,
USA) in dew point mode. The chambers containing the
samples were then placed in a freezer at –20˚C for 2 h.
After thawing and equilibrating at 25˚C for 3 h, the
was determined. The turgor potential (
t) was calculated
as the difference between
2.3. Traits Associated with the Adult Plants
The data for the adult plants used in this work are
mean values for four years obtained during assays per-
formed in a rain shelter, with plants growing under ter-
minal water deficit conditions [27]. The rain shelter was
divided into two areas (irrigated and water deficit condi-
tions) separated by a 1.5 m wide central corridor. In the
water deficit plots, each genotype was deprived of water
when the plants reached the flag leaf stage, stage 41 on
Á. González et al. / Agricultural Science 2 (2011) 159-166
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Ta b le 1 . Length and relative growth of coleoptiles of eight barley genotypes grown in Petri dishes under irrigated and water stress
conditions by evaporative loss.
Irrigated Water stress
Genotype Initial length
(mm) Final length
(mm) Relative growthInitial length
(mm) Final length
(mm) Relative growth Mean relative
L31 20.97 83.53 3.00 17.53 43.80 1.51 2.25
L40 21.43 91.60 3.28 24.23 61.03 1.53 2.40
L47 22.07 101.8 3.64 21.47 49.60 1.31 2.37
Tipper 21.73 83.50 2.84 22.20 46.67 1.11 1.97
Plaisant 29.60 103.1 2.49 29.60 55.57 0.88 1.68
Viva 26.87 96.70 2.62 22.93 57.77 1.54 2.08
Reinette 23.83 97.97 3.12 25.23 49.10 0.95 2.03
Albacete 26.53 107.4 3.05 24.17 66.87 1.77 2.41
Mean 24.13 95.70 3.00 23.42 53.80 1.32
S.E.D* 0.11 0.08 0.09
D.F. 14 14 14
*Standar error of mean diferences to compare genotypes under irrigated and water stress conditions.
the Zadoks scale [28]. Plots were arranged in four repli-
cations and the different genotypes distributed randomly
in each of them.
Samples were taken from each plot from the begin-
ning of the water stress treatment until maturity in order
to estimate osmotic adjustment (OA). For this, weekly
samples of flag leaves from one plant in each subplot
were collected at 6:45 (GMT), placed in a sealable plas-
tic bag, and transported to the laboratory. These leaves
were then cut longitudinally into two symmetrical halves.
One was immediately weighed in order to determine the
relative water content (RWC) using the formula:
RWC (%) = [(fresh weight – dry weight)/turgid weight –
dry weight)] × 100
The turgid weight was obtained by leaving overnight
the same half of the leaf in destilled water at 5˚C in
darkness, and dry weight after 24 h at 80˚C. The other
half was used to determine
s. To estimate the osmotic
adjustment of each genotype, the correlation between
and RWC was determined from the corresponding linear
regressions. The RWC values for an
s of –3 MPa was
recorded following the criteria of Morgan (1983) [29].
The ears from the center square meter of each plot
were threshed in a threshing machine and grain of each
genotype was weighed.
2.4. Statistical Analysis
Genotype and stress treatments were analysed by per-
forming two-way ANOVA analyses. When significant
differences between treatments or genotypes were de-
tected (P < 0.05), mean differences were compared with
a t test. The relationships between relative growth and
the different variables examined were analysed by de-
termining Pearson’s correlation coefficients. Significance
was determined using the Student t test. All calculations
were performed using Statistica 5.1 software [30].
The effect of water deficit on coleoptile growth are
presented in Tables 1 and 2 according to the water
deficit was induced
3.1. Water Deficit Induced by Evaporation
Ta ble 1 shows the growth data for the coleoptiles of
the eight barley genotypes grown under control and wa-
ter deficit, evaporation method, conditions. The mean
growth of the control coleoptiles (3 mm) was signifi-
cantly greater than that of the treatment coleoptiles (1.32
mm) for all genotypes together, (P < 0.01). The growth
of the controls was always greater than that of the treat-
ment coleoptiles.
Differences were also detected, however, between the
growth of the different genotypes, with three groups dis-
cernable. The group showing the greatest relative growth
was composed of the genotypes L40, L47, Albacete and
L31. This group was followed by one composed of
Reinette and Viva. The group showing the least relative
growth was made up of Plaisant and Tipper.
The correlation found between relative growth and
was high, non-significant for the controls but significant
for the stress treatment plants (P < 0.05) (Figure 1).
3.2. Water Deficit Induced by PEG
Table 2 shows the mean relative growth values for the
ight genotypes in the presence and absence of PEG. The e
Á. González et al. / Agricultural Science 2 (2011) 159-166
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Figure 1. Relationship between relative growth of coleoptiles and water potential in control and water stress in-
duced in evaporative loss of eight barely genotypes grown in Petri dishes.
mean relative growth of the control plants (2.83 mm)
was significantly greater than that recorded for the
treatment plants as a whole (2.52 mm) although the dif-
ference between the control and treatment was not sig-
nificant for all genotypes.
Significant differences in relative growth were also
seen between the different genotypes (P < 0.001). Again,
three groups could be discerned. The first, with the
greatest relative growth, included L31, L40 and L47, the
second, with intermediate growth, included Tipper, Reinette
and Albacete, and the third, with the least growth, in-
cluded Plaisant and Viva.
The differences in growth between the control and
treatment plants were smaller in this assay than in the
previous assay for all genotypes. This may have been
due to the dehydration process in the second experi-
ment being slower, allowing time for the plants to
bring into play water deficit tolerance mechanisms
that favoured growth under these conditions (note that
the growth of the control plants in both experiments is
very similar and the correlation was significant (r =
0.77, P < 0.01), while growth under the PEG stress
conditions was greater than under the evaporation
conditions and the correlation was not significant (r =
3.3. Maintenance of Turgor in the
of the control plants was greater than that of
the treatment plants in both experiments and for all
genotypes (Table 3). The
t of the control plants was
lso higher in the control plants. The variety Plaisant and a
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Tab le 2. Length and relative growth of coleoptiles of eight barley genotypes grown in Petri dishes with distilled water (control) and
with a PEG solution (stress treatment).
Irrigated Stress treatment
Genotype Initial length (mm)Final length (mm) Relative
growth Initial length (mm)Final length (mm) Relative
growth Mean relative
L31 14.70 65.90 3.48 18.10 66.00 2.66 3.08
L40 18.93 78.47 3.15 18.47 74.87 3.05 3.10
L47 19.67 78.77 3.01 18.83 74.93 2.98 2.99
Tipper 20.53 72.60 2.61 19.43 65.87 2.46 2.53
Plaisant 28.37 92.90 2.29 27.90 85.90 2.08 2.18
Viva 21.77 78.10 2.60 22.70 68.13 2.01 2.30
Reinette 24.30 88.23 2.65 23.97 82.90 2.46 2.55
Albacete 22.40 85.73 2.84 22.70 77.83 2.43 2.63
Mean 21.33 80.09 2.83 21.50 74.55 2.52
S.E.D.* 0.24 0.18 0.17
D.F. 14 14 14
*Standar error of mean differences to compare genotypes under irrigated and stress conditions.
Table 3. Water potential (
), maintenance of turgor (
= –2 MPa), osmotic adjustment (OA) [Relative water content RWC =
–3 MPa], and grain yield under water stress conditions.
Coleoptiles Adult plant*
Irrigated Water stress Flag-leaf
t (
= –2MPa)
t (
= –2MPa) OA (CHR = –3MPa) Grain weight (g·m–2)
L31 –0.165 0.189 –1.83 0.116 72.51 215.84
L40 –0.102 0.144 –2.17 0.083 71.39 283.54
L47 –0.095 0.148 –2.32 0.059 63.37 188.47
Tipper –0.203 0.057 –1.95 0.051 63.47 186.90
Plaisant –0.183 0.201 –2.18 0.021 62.28 151.05
Viva –0.165 0.166 –1.21 0.036 62.22 116.05
Reinette –0.182 0.114 –3.00 0.059 64.28 194.99
Albacete –0.062 0.225 –1.05 0.030 59.83 161.67
Mean –0.145 0.156 –1.964 0.057 64.92 187.31
*All values are means of four years under water stress conditions (González 2001).
the breeding line L31 had the highest
t values, 0.201
MPa and 0.189 MPa respectively, while Tipper had the
lowest, 0.057 MPa. In the PEG water deficit treatment
the genotypes with the highest
t values were L31 and
L40, 0.116 MPa and 0.083 MPa respectively, while
Plaisant, Albacete and Viva had the lowest
t values,
0.021 MPa, 0.03 MPa and 0.036 MPa respectively.
Reinette, Tipper and L47 showed intermediate
t values.
The osmotic adjustment behaviour of the genotypes in
the PEG water deficit treatment was similar in the col-
eoptile stage to that seen in adult plants. Breeding lines
L31 and L40 were those with the greatest osmotic ad-
justment capacity with relative water content (RWC) at
–3 MPa of 72.51 and 71.39 respectively (Ta b l e 3 ). The
varieties Plaisant, Viva and Albacete showed the lowest
values at 62.28, 62.22 and 59.83 respectively. This ex-
plains the strong correlation found between the osmotic
adjustment seen in the adult plants and seedling turgidity
(P < 0.01) (Figure 2(a)), as well as the strong correla-
tion seen between relative growth under water deficit
and seedling turgidity (Figure 2(b)).
The correlations found between osmotic adjustment in
the adult plants and the relative growth of the coleoptiles
was not significant for the controls, but significant (P <
0.05) for the water deficited plants in the PEG assay
(Ta ble 4 ). These correlations were less strong, non-sig-
nificant, in the first experiment for both the control and
treatment plants. This is probably due to the more rapid
dehydration achieved with evaporation than the PEG
treatment; such rapidity may have impeded the ability to
make efficient use of adaptation mechanisms such as
osmotic adjustment.
The correlation between grain weight and the relative
growth of the coleoptiles was significant under the PEG-
induced water deficit conditions, but not in the evapora-
tion-induced water deficit conditions (Table 4).
The present results indicate that coleoptile growth is
directly related to osmotic adjustment under water defi-
cit conditions. Osmotic adjustment also has a positive
ffect on turgor, as shown by the positive, significant e
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Figure 2. (a) Relationship in coleoptiles and osmostic adjustment estimate (OA) (RWC = –3 MPa) in adult plant
and (b) relative growth of coleoptiles grown in the presence of a PEG solution.
Table 4. Linear correlation coefficients between relative
growth of coleoptiles under two water stress treatments and
osmotic adjustment (OA) and grain yield in adult plant.
Evaporative loss PEG solution
OA Grain weight OA Grain weight
growth Con-
0.27 0.29 0.67 0.41
growth Stress 0.61 0.11 0.74* 0.86**
*, **significant at the 0.5 and 0.01 probability levels, respectively.
correlation (P < 0.01) between seedlings turgor and os-
motic adjustment in adult plants (Figur e 2).
Variation was seen with respect to the growth of the
coleoptiles under both control and treatment conditions.
Similar results have been reported by other authors for
wheat [31,32], triticale [32], and pea [33].
A significant correlation was obtained between the
relative growth of the coleoptiles and
under evapora-
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tion-induced water deficit conditions (Figure 1). How-
ever, the correlation with osmotic adjustment was not
significant. When water deficit was induced with PEG,
the correlation between osmotic adjustment and relative
growth was significant (Table 4). In the first case the
mean relative growth of the control coleoptiles was 56%
greater than that shown by those under water deficit
(Table 1). In the PEG assay, however, this difference fell
to just 11% (Ta ble 2 ). This probably reflects a more ef-
ficient osmotic adjustment in the PEG assay, a conse-
quence of the dehydration process being slower. The
level of osmotic adjustment reached depends on factors
such as the degree of water deficit and the rate at which
it develops. The osmotic adjustment that occurs is less if
water deficit develops quickly [34]. The results confirm
the influence of osmotic adjustment on turgor mainte-
nance and growth in barley coleoptiles under water defi-
cit conditions. Similar results were obtained in rice and
pearl millet [22,35] who reported osmotic adjustment to
be the trait that made the greatest contribution towards
the maintenance of turgor and seedling growth under
water deficit conditions. Studding the response of two
wheat cultivars to osmotic stress induced by PEG, Guóth
et al. [36] reported the water potential of the tolerant
cultivar did not change significantly under stress condi-
tions, whereas significant differences were observed in
the sensitive cultivar. In sunflower it has been reported
that, with respect to water status in the leaves, the rank-
ing of the genotypes is maintained over the growth of the
plants [37].
In both assays, L31 and L40 were among the geno-
types showing the greatest growth, while Plaisant and
Viva were among those with the relatively smallest
growth. This classification corresponds with that found
for osmotic adjustment in the adult plants, with L40 and
L31 showing the greatest osmotic adjustment capacity
and Plaisant and Viva the least (Table 3).
Both growth and the behaviour of the
t for the barley
genotypes studied were similar to those obtained for the
flag leaf osmotic adjustment and grain weight, as con-
firmed by the correlation detected between osmotic ad-
justment in adult plants and the turgor maintained by the
seedling (P < 0.01) (Figure 2(a)). In addition, the corre-
lation found between the relative growth of the coleop-
tiles and grain weight was high (P < 0.01) under the
PEG water deficit conditions. These results show the
value of coleoptile growth in response to water deficit as
a selection trait in barley breeding programmes. The
correlation between coleoptile growth and yield under
water deficit has also been reported for wheat (Moud
and Maghsoudi 2008). The osmotic adjustment of adult
barley plants correlates significantly (P < 0.01) with the
ability to maintain turgor under water deficit conditions
during the seedling stage (Figure 1), and grain yield
correlates with coleoptile relative growth under water
deficit conditions (Ta ble 4 ). The present results indicate
that seedlings studies offer advantages in barley selec-
tion programmes. More work should be performed in
this area.
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