Spatial distribution of Pb and its correlation at different grain positions among wheat varieties for specific end-uses

doi:10.4236/as.2013.49068

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Vol.4, No.9, 509-515 (2013) Agricultural Sciences

http://dx.doi.org/10.4236/as.2013.49068

Spatial distribution of Pb and its correlation at

different grain positions among wheat varieties for

specific end-uses

Fei Xiong1*, Zhaodi Dong2, Xurun Yu1, Liang Zhou1, Zhong Wang1

1College of Bioscience and Biotechnology, Yangzhou University, Yangzhou, China;

*Corresponding Author: [email protected]

2College of Agriculture, Yangzhou University, Yangzhou, China

Received 23 June 2013; revised 23 July 2013; accepted 15 August 2013

permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

ABSTRACT

The relative content of Pb and its correlation

were investigated in endosperm, aleurone layer

and pericarp respectively among different wheat

varieties for specific end-uses (WVFSE) using

scanning electron microscope (SEM) equipped

with the energy dispersive X-ray spectroscope

(EDS). The results showed that Pb contents in

grains at different positions followed the order

of endosperm > pericarp > aleurone. The differ-

ences of Pb contents varied among the WVFSE,

and wheat with strong gluten had a highest av-

erage content of Pb, while wheat with medium

gluten had a lowest one. There were significant

third order equation correlations between Pb

content in endosperm and that in aleurone layer

and that in pericarp, respectively. And good

correlation coefficients were obtained. However,

the correlation differed at different position

among WVFSE, which indicated that Pb con-

tents in endosperm, aleurone layer and pericarp

were regulated by each other.

Keywords: Lead; Correlation; Wheat Varieties for

Specific End-Uses; Grain Position

1. INTRODUCTION

The contamination of heavy metals into the environ-

ment is becoming a worldwide concern due to their tran-

sfer in food chain via the uptake of crops [1,2]. Pb has

long been recognized as one of most toxic heavy miner-

als to human beings [3,4]. Pb absorbed by human body

disturbs many body processes and is harmful to many

organs and tissues such as the heart, bones, nervous sys-

tems and so on [5,6].

Wheat is one of most important food crops in the

world, especially in China, due to the highest total yields

and the most abundant types of food processing [7,8].

However, there are quite large differences in grain com-

position and processing quality among wheat cultivars.

Based on the gluten contents and specific end uses,

wheat cultivars are divided into three classes, i.e. wheat

with strong gluten, wheat with medium gluten and wheat

with weak gluten, respectively [7].

As Pb has strong wall penetrating ability and migra-

tion ability, its toxicity in wheat causes swelling of

chloroplast in leaves cells [9], mitosis disturbances in

root meristematic cells [10] and decreasing activities of

antioxidant enzymes [11]. There were many factors af-

fecting absorption of Pb in wheat including soil features

[12,13], PH values [14], other mineral nutrients [15] and

wheat varieties [16,17]. Study about Pb has been docu-

mented well, however, not much information is available

about distribution of Pb and its correlation analysis at

different position in wheat varieties for specific end-uses.

With this background, in this report 15 genotypes of

wheat grains were chosen to investigate the differences

among the Pb contents at different positions and their

relationships.

2. MATERIAL AND METHODS

2.1. Materials

The experiment was done at Yangzhou University,

Yangzhou, China (32˚30'N, 119˚25'E) from October 2011

to July 2012. Based on wheat specific end-uses, 3 classes

of wheat varieties, i.e., wheat with strong gluten, wheat

with medium gluten and wheat with weak gluten respec-

tively, were used and grown on the same field (Table 1).

The sowing date was 25 November. The field soil is

F. Xiong et al. / Agricultural Sciences 4 (2013) 509-515

510

sandy loam [Typic fluvaquents, Entisols (US taxonomy)]

which contains organic materials at 2.45% and available

nitrogen (N), phosphorus (P) and potassium (K) of 106,

33.8 and 66.4 mg·kg−1, respectively. Available N as urea

at 75 kg·hm−1 was applied into the soil on the day of

sowing and at the jointing stage, respectively. All uni-

form agronomic practices were carried on for all varieties.

When wheat ripe, the grains were collected for the

analysis of elements

2.2. Observation of Wheat Grain Structure

Using Scanning Electron Microscopy

(SEM)

Representative grains were chosen and fractured in the

middle region of grain by applying a slight pressure with

a razor blade. During fracturing, the efforts were made to

produce no contact between the razor blade and the frac-

tured surface of grains. The thickness of slices was about

3 mm. Fractured grains were mounted on the specimen

stub and sputtered with gold on the fractured region. The

wheat grains were observed using SEM (XL30 ESEM,

Philips, Holland) at 20 kV and the air pressure in the

sample chamber was 4 Torr.

2.3. X-Ray Electron Probe Microanalysis

When the grains were being observed under the SEM,

the energy spectrum was also analyzed with the energy

dispersive X-ray spectroscope attached to the SEM. The

relative content of Pb in pericarp, aleurone layer and

endosperm, respectively, was determined, which was

shown as atomic content among ten elements (Mg, Al, P,

S, K, Ca, Cr, Cu, Cd, Pb) (Fig ure 1). Each kind of sam-

ple and the same position were scanned for 3 times re-

spectively.

Table 1. Characterization of wheat varieties for specific end-uses.

Classes Representative varieties Protein content (%)Wet gluten content (%) Food types used

Strong Gluten Qing 11,Waimai 33, Xumai30, Yannong 19, Zheng 9023 ≥15% ≥32% Bread, dumpling

Medium Gluten E21, Yangfu 4, Yangmai 11, Yangmai 16, Yangmai 158 14% ± 1% 30% ± 3% steamed bread, noodles

Weak Gluten Yangfu2, Yangmai 13, Yangmai15, Yangmai 18, Yangmai 19<13% <20% Cookies, cakes, pastries

Figure 1. SEM-EDS images of mature wheat grain; (A) SEM images of transversely section of wheat grain; (B)

Magnification of A showing details of pericarp, aleurone and endosperm, respectively; (C) EDS image of pericarp;

(D) EDS image of aleurone; (E) EDS image of endosperm.

F. Xiong et al. / Agricultural Sciences 4 (2013) 509-515 511

Statistical analysis

SPSS 19.0 software was carried out to analyze vari-

ance test and significance, and the relative analysis and

the graph were done with Sigmaplot 12.0 software.

3. RESULTS

3.1. Distribution of Pb Content at Different

Position in Wheat Varieties for Specific

End-Uses (WVFSE)

The spatial distribution of Pb in different positions

differed and the order was endopsperm > pericarp > aleu-

rone (Table 2). Pb contents were different among three

classes of wheat varieties. Wheat with strong gluten had

a highest average content of Pb in whole grain, while

wheat with medium gluten had a lowest. Moreover, in

the same position the relative content of Pb distributed

differently among three classes of wheat varieties. In

endosperm and aleurone layer, Pb content changed as

wheat with strong gluten > wheat with medium gluten >

wheat with weak gluten, but in pericarp, it followed the

order of wheat with strong gluten > wheat with weak

Table 2. Relative content of Pb at different positions of WVFSE.

Classes Representative varieties EndospermAleurone layer PericarpTotal

Strong gluten Qing 11,Waimai 33, Xumai30, Yannong 19, Zheng 9023 8.84a 1.00a 3.47a 13.3a

Medium gluten E21, Yangfu 4, Yangmai 11, Yangmai 16, Yangmai 158 4.07b 0.85a 2.13b 7.05b

Weak gluten Yangfu2, Yangmai 13, Yangmai15, Yangmai 18, Yangmai 19 3.89b 0.35b 3.22a 7.46a

Different letters means difference significant at P < 0.05 and the same letters means difference no significant.

(a) (b)

(c)

Figure 2. Relationship between the relative content of Pb in the endosperm (A) and that in aleurone layer (B) and that in peri-

arp (C) among wheat varieties with strong gluten. c

F. Xiong et al. / Agricultural Sciences 4 (2013) 509-515

512

gluten > wheat with medium gluten. This indicated Pb

contents in wheat with strong gluten was the highest at

any position, probably due to genetic differences.

3.2. The Relations between Pb Contents at

Different Position among WVFSE

The relations of Pb contents at different position of

WVFSE were performed with curve fitting and the cor-

relations were fitted well with three order equation (Fig-

ures 2-4 and Tables 3-5), which showed the Pb contents

at different position were influenced by each other.

Among wheat varieties with strong gluten, the rela-

tions of Pb content at different position and the relevant

equations were shown in Figure 2 and Ta ble 3, respec-

tively. The correlation between Pb content in endosperm,

that in aleurone layer and that in pericarp were highly

significant at P < 0.01 and significant at P < 0.05, respec-

tively, which indicated Pb distribution in endosperm

could affect that of the two positions; Correlation co-

effi-cient showed degree of influence followed the order

of aleurone layer > pericarp. The correlation between Pb

content in aleurone layer, that in pericarp and that in en-

dosperm were not significant, which indicated Pb content

in aleurone layer had no effect on that of other two posi-

tions. The correlation between Pb content in pericarp,

that of endosperm and that of aleurone were significant

at P < 0.05 and highly significant at P < 0.01, respec-

tively, correlation coefficient showed degree of influence

changed as aleurone layer > endosperm.

Among medium gluten wheat, the relations of Pb con-

tent at different position and the relevant equations were

shown in Figure 3 and Ta ble 4, respectively. The corre-

lation between Pb content in endosperm and that in peri-

carp were highly significant at P < 0.001 but not signifi-

cant for that in aleurone layer, which showed Pb content

in endosperm affected greatly that in pericarp; The cor-

relation between Pb content in aleurone, that of pericarp

and that of endosperm were significant at P < 0.05 and

(a) (b)

(c)

Figure 3. Relationship between the relative content of Pb in the endosperm (A) and that in aleurone layer (B) and that in peri-

carp (C) among wheat varieties with medium gluten.

F. Xiong et al. / Agricultural Sciences 4 (2013) 509-515 513

(a) (b)

(c)

Figure 4. Relationship between the relative content of Pb in the endosperm (A) and that in aleurone (B) and that in pericarp (C)

among wheat varieties with weak gluten.

Table 3. The correlation of relative content of Pb at different position of wheat varieties with strong gluten.

Endosperm Aleurone layer Pericarp

Endosperm 1 232

0.8958 0.6032

0.1163 0.00450.9756

xxR**





 

32 *

1.93750.89560.2066

0.0081 0.8479

 



Aleurone layer 2

15.4986 121.5540

149.5574

38.38080.5185.

 



s

1 2

4.9202 11.3663

12.5710

2.87910.68106..





s

Pericarp

32 *

5.0571 13.43126.1301

0.5560 0.8245

 



32 **

0.4391 0.65440.3034

0.0347 0.9758

 

 1

Note: n.s. indicates not significant,*indicates the correlation is significant at p < 0.05, **: indicates the correlation is significant at p < 0.01, ***: indicates the

correlation is significant at p < 0.001.

highly significant at P < 0.01, respectively, which indi-

cated that degree of influence followed the order of peri-

carp > endosperm. The correlation between Pb content in

pericarp, that of endosperm and that of aleurone layer

were highly significant at P < 0.01 and at P < 0.001, re-

spectively, which showed Pb distribution in pericarp af-

fected greatly that of the two positions.

Among weak gluten wheat, the relations of Pb content

at different position and the relevant equations were

shown in Figure 4 and Ta b le 5, respectively. The corre-

lation between Pb content in endosperm, that of aleurone

and that of pericarp were not significant, this indicated

Pb content in endosperm did not affect that of other both

ositions; The correlation between Pb content in aleu- p

F. Xiong et al. / Agricultural Sciences 4 (2013) 509-515

514

Table 4. The correlation of relative content of Pb at different position of wheat varieties with medium gluten.

Endosperm Aleurone layer Pericarp

Endosperm 1

0.3057 0.67670.1846

0.01260.6958..

xR ns

 



3 2***

0.0638 1.65010.4372

0.32220.9823

 



Aleurone

layer

32 *

15.137787.0232121.1866

51.8678 0.7794

 



32 **

5.4213 31.812646.1262

21.0439 0.9499

 



Pericarp 32 **

0.02919.62815.7626

0.7882 0.9527

 



3 2***

0.2454 0.77740.8905

0.1292 0.9988

 

 1

Note: n.s. indicates not significant,*: indicates the correlation is significant at P < 0.05, **: indicates the correlation is significant at P < 0.01, ***: indicates the

correlation is significant at P < 0.001.

Table 5. The correlation of relative content of Pb at different position of wheat varieties with weak gluten.

Endosperm Aleurone layer Pericarp

Endosperm 1

0.1079 0.09530.0154

0.00160.6871 . .

yxx

Rns

 



1.91113.52221.1106

0.08850.6886..

yxx

 

s

Aleurone layer

32 ***

14.3736 210.3609718.7944

728.2636 0.9988

 



32 **

7.1491 127.3948390.2065

344.3020 0.9086

 



Pericarp

59.4457 66.382124.0915

2.65070.4190..

xR ns

 



32 **

7.4239 8.14992.8833

0.3126 0.8813

 



Note: n.s. indicates not significant,*: dicates the correlation is significant at P < 0.05, **: indicates the correlation is significant at P < 0.01, ***: indicates the

correlation is significant at P < 0.001.

rone, that of pericarp and that of endosperm were highly

significant at P < 0.001 and at P < 0.01, respectively,

which showed Pb distribution significantly influenced

that of the two positions. The correlation between Pb in

pericarp and that in aleurone were significant at P < 0.01

but not significant for that in endosperm, which showed

Pb content in pericarp was regulated by endosperm.

The results also indicated Pb correlation varied among

different WVSE. Pb contents in aleurone layer and peri-

carp were regulated by endosperm and degree of influ-

ence followed the order of wheat with strong gluten >

wheat with medium gluten > wheat with weak gluten; Pb

contents in endosperm and pericarp were affected by that

in aleurone and the order changed as wheat with weak

gluten > wheat with medium gluten > wheat with strong

gluten; Pb contents in endosperm and aleurone layer

were adjusted by pericarp and the order changed as me-

dium gluten > strong gluten > weak gluten.

4. DISCUSSION

Generally speaking, there were two approaches to re-

duce Pb accumulation in grain, one is to breed new

genotypes with low Pb concentrations in grain [15,17],

the other is to use some agricultural practices [16,18].

Dietary fibers in wheat bran can also obviously bind Pb

to prevent the body from toxicity [19].

Distribution of Pb varied with different organs and

followed the order of root > shoots > shells > grains.

Moreover, Pb contents in different parts of wheat plants

were mainly relative to the bound-to-carbonate metal

fractions [20]. In the present study, there were genetic

differences in Pb enrichment, which reflected the dif-

ferences of Pb contents in different WVFSE. Because the

wheat cultivars were grown in the same fields and envi-

ronmental conditions, we can confirm that the Pb distri-

bution was controlled by polygene quantitative charac-

ters, which agrees with the findings of previous experi-

ment studies [21,22].

We also found that there were significant third order

equation correlations between Pb content in endosperm

and in aleurone layer and in pericarp, which indicated

that Pb accumulation in different position of WVFSE

was influenced by each other. Furthermore, there were

differences in the regulation of Pb distribution among the

different positions. When wheat grains were ground into

flour, the aleurone, pericarp and germ should be removed

from the endosperm. Thus, the Pb accumulation in en-

dosperm was closely linked with human’s health, which

was regulated by other positions of wheat grain, particu-

larly in aleurone and pericarp.

Therefore, in order to reduce the risk of Pb toxicity

from the daily consumption of wheat, we should choose

the genotypes with low Pb content as the main wheat

cultivars. At the same time, some suitable measures

should be also taken to remove potential hazards of Pb

[16,18].

F. Xiong et al. / Agricultural Sciences 4 (2013) 509-515 515

5. ACKNOWLEDGEMENTS

The research was supported by the National Natural Science Foun-

dation (31171482), Jiangsu Natural Science Foundation (BK2011445),

Jiangsu Graduate Innovation Project (CXLX12-0910)

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