Response of coleoptiles to water deficit: growth, turgor maintenance and osmotic adjustment in barley plants (Hordeum vulgare L.)

doi:10.4236/as.2011.23022

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Vol.2, No.3, 159-166 (2011)

doi:10.4236/as.2011.23022

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: [email protected]

2Centro de Recursos Fitogenéticos, Alcalá de Henares, Spain.

Received 11 January 2011; revised 23 May 2011; accepted 25 July 2011.

ABSTRACT

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

1. INTRODUCTION

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 effect―either

Á. González et al. / Agricultural Science 2 (2011) 159-166

160

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. MATERIALS AND METHODS

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

Parameters

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



and



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

161161

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

growth

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].

3. RESULTS

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

162

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 =

0.30).

3.3. Maintenance of Turgor in the

Coleoptiles

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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163163

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

growth

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

Genotype



(MPa)



t (



= –2MPa)



(MPa)



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

Á. González et al. / Agricultural Science 2 (2011) 159-166

164

(a)

(b)

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

Relative

growth Con-

trol

0.27 0.29 0.67 0.41

Relative

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).

4. DISCUSSION

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-

Á. González et al. / Agricultural Science 2 (2011) 159-166

165165

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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