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:
2College of Agriculture, Yangzhou University, Yangzhou, China
Received 23 June 2013; revised 23 July 2013; accepted 15 August 2013
Copyright © 2013 Fei Xiong et al. This is an open access article distributed under the Creative Commons Attribution License, which
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
yx
xxR**


 
2
32 *
1.93750.89560.2066
0.0081 0.8479
yx
xR
 

x
Aleurone layer 2
32
15.4986 121.5540
149.5574
38.38080.5185.
yx
x
x
Rn
 

s
1 2
32
4.9202 11.3663
12.5710
2.87910.68106..
yx
x
x
Rn


s
xx
Pericarp
2
32 *
5.0571 13.43126.1301
0.5560 0.8245
yx
xR
 

2
32 **
0.4391 0.65440.3034
0.0347 0.9758
yx
xR
 
 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
2
32
0.3057 0.67670.1846
0.01260.6958..
yx
xR ns
 

xx
2
3 2***
0.0638 1.65010.4372
0.32220.9823
yx
xR
 

Aleurone
layer
2
32 *
15.137787.0232121.1866
51.8678 0.7794
yx
xR
 

2
xx
xx
1
2
32 **
5.4213 31.812646.1262
21.0439 0.9499
yx
xR
 

Pericarp 32 **
0.02919.62815.7626
0.7882 0.9527
yx
xR
 

2
3 2***
0.2454 0.77740.8905
0.1292 0.9988
yx
xR
 
 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
2
32
0.1079 0.09530.0154
0.00160.6871 . .
yxx
x
Rns
 

2
32
1.91113.52221.1106
0.08850.6886..
yxx
x
Rn
 
s
Aleurone layer
2
32 ***
14.3736 210.3609718.7944
728.2636 0.9988
yx
xR
 

xx
x
1
2
32 **
7.1491 127.3948390.2065
344.3020 0.9086
yx
xR
 

Pericarp
2
32
59.4457 66.382124.0915
2.65070.4190..
yx
xR ns
 

x2
32 **
7.4239 8.14992.8833
0.3126 0.8813
yx
xR
 

1
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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