genotypic variation in partitioning of dry matter and manganese between source and sink organs of...
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ORIGINAL PAPER
Genotypic variation in partitioning of dry matter and manganesebetween source and sink organs of rice under manganese stress
Shalini Jhanji • Upkar Singh Sadana
Received: 10 February 2014 / Revised: 19 March 2014 / Accepted: 27 March 2014
� Springer-Verlag Berlin Heidelberg 2014
Abstract
Key message Genetic variability in dry matter and
manganese partitioning between source and sink organs
was the key mechanism for Mn efficient rice genotypes
to cope with Mn stress.
Abstract Considerable differences exist among cereal
genotypes to cope manganese (Mn) deficiency, but the
underlying mechanisms are poorly understood. Minimal
information regarding partitioning and/or remobilization of
dry matter and Mn between source and sink organs exists
in rice genotypes differing in Mn efficiency. The present
study was aimed to assess the growth dynamics in terms of
dry matter and Mn remobilization in the whole plant
(leaves and tillers as source and panicles and grains as sink)
during the grain development in diverse rice genotypes.
The efficient genotypes accumulated higher dry matter than
inefficient genotypes under low Mn level. The transloca-
tion index i.e., uptake in grain/total uptake was 0.11 in
efficient genotype (PR 116) and 0.04 in inefficient geno-
types (PR 111). The efficient genotype had higher grain Mn
utilization efficiency of 0.71 in comparison to 0.48 of
inefficient genotype indicating that in efficient genotype,
Mn in grain produces more dry matter than inefficient
genotypes. The efficient genotypes also had higher flag leaf
area and nitrate reductase activity. The source of efficient
genotypes contributed to a greater extent to developing
sink but further mobilization to grain was hindered by
panicle. The panicle of inefficient genotypes had higher per
cent of Mn uptake than efficient genotypes indicating that
Mn was least mobilized from panicle to grain in inefficient
genotypes. The lower per cent uptake of Mn in efficient
genotypes indicated that Mn was mobilized from panicle to
developing grain and this led to higher Mn translocation
index in grain of efficient genotypes. The uptake parti-
tioning revealed that source of all genotypes mobilized the
Mn towards the sink to almost same extent but it was the
panicle where highest per cent uptake per plant was in
inefficient genotypes and lowest in efficient genotypes. The
lowest per cent uptake in panicle of efficient genotypes
revealed that it supported developing grain to have highest
translocation index.
Keywords Manganese � Dry matter partitioning � Grain
filling period � Remobilization � Source–sink relationship
Abbreviations
ANOVA Analysis of variance
C Carbon
CaCO3 Calcium carbonate
DAA Days after anthesis
DTPA Diethylenetriaminepentaacetic acid
HClO4 Per chloric acid
HNO3 Nitric acid
K Potassium
KCl Potassium chloride
KH2PO4 Potassium dihydrogen phosphate
KNO3 Potassium nitrate
L Leaves
LSD Least significant difference
Mn Manganese
Communicated by A. Dhingra.
Electronic supplementary material The online version of thisarticle (doi:10.1007/s00299-014-1611-x) contains supplementarymaterial, which is available to authorized users.
S. Jhanji (&) � U. S. Sadana
Department of Soil Science, Punjab Agricultural University,
Ludhiana 141004, India
e-mail: [email protected]
123
Plant Cell Rep
DOI 10.1007/s00299-014-1611-x
MnSO4�H2O Manganese sulphate
NRA Nitrate reductase activity
P Phosphorus
ppm Parts per million
PQ Partitioning quotient
r Correlation coefficient
SPAD Soil plant analysis development
T Tiller
Introduction
Since the ‘‘Green Revolution’’, intensive cropping, culti-
vation of high-yield genotypes, improved agricultural
mechanization, production of macronutrient fertilizers with
low impurities of trace elements, and using modern irri-
gation system have resulted in higher crop production per
unit area and greater depletion of soil phytoavailable
micronutrients (Khoshgoftarmanesh et al. 2010). Devel-
oping micronutrient-efficient genotypes would be sustain-
able and cost-effective method for alleviating food-chain
micronutrient deficiency, malnutrition in humans.
In last few decades, manganese deficiency has emerged
as an important nutritional problem worldwide affecting
the crop growth and yield in calcareous soils with high pH
(Yang et al. 2007). In Punjab, where rice wheat cropping
system is predominant, several studies have been done to
screen diverse wheat genotypes for high Mn efficiency and
understand the mechanism for their differential efficiency
(Sadana et al. 2002, 2005; Jhanji et al. 2013a, b) but such
studies with rice are scanty. Visual symptoms of Mn
deficiency are not observed in flooded rice, as reducing
conditions on soil submergence increase Mn solubility, but
Mn deficiency imposes threat on growth, yield, and grain
nutritional status in rice. Till date, few reports are available
revealing Mn efficiency in diverse rice genotypes (Fageria
et al. 2008; Jhanji et al. 2012).
Rice is one of the world’s most important staple food
crops, and second most cultivated cereal after wheat (Fa-
geria 2007). Breeding for Mn dense cultivars of rice is a
powerful tool to combat Mn malnutrition worldwide.
Keeping in view the increasing scenario of Mn deficiency
in soils, importance of rice as a staple food crop and lack of
reports pertaining to Mn efficiency in rice, field experi-
ments were conducted with diverse genotypes to screen Mn
efficient genotypes. The genotypes with high relative yield
i.e., yield at low Mn/yield at high Mn and high relative Mn
uptake were considered to be efficient genotypes (Jhanji
et al. 2012). Jhanji et al. (2011) reported that morpho-
physiological characteristics such as longer roots, more leaf
area, higher nitrate reductase activity and soil plant
analysis development (SPAD) index were also associated
with efficient genotypes of rice.
Plants that grow in Mn deficiency during grain filling
stage will depend on the amount of Mn taken up by the
roots during grain development and the amount redistrib-
uted to the grain from vegetative tissue via phloem i.e.,
remobilization (Waters and Grusak 2008). Fang et al.
(2008) reported that Fe concentration in rice grains could
be increased by enhanced root uptake combined with stem/
leaf efflux transport activity. Remobilization of reserves to
supply rice grains has been also emphasized in the earlier
studies (Wu et al. 2010; Yoneyama et al. 2010). The Mn
uptake and/or mobility within shoot and to the grain (i.e.,
mobilization) is mainly affected by Mn application and
growth stages (Pearson and Rengel 1994); sucrose status
and humidity (Pearson et al. 1996); heat stress which
generally increases Mn uptake (Dias et al. 2009) and plant
genotypes (Hocking et al. 1977). So, we need to focus on
the behavior of Mn in terms of its mobility within different
organs leading to its better distribution and partitioning in
plant. Phloem mobility of Mn is very low and it can reach
glumes directly via xylem in mature wheat plants or can be
first transferred from xylem to phloem and then reach the
glumes via phloem in young plants (Riesen and Feller
2005) though the extent of Mn mobility in phloem varies
with plant species (Epstein 1971). Pearson and Rengel
(1994) reported poor remobilization of Mn in wheat grains
due to poor phloem mobility where as Sperotto et al.
(2012) reported remobilization of Mn from stem/sheath in
rice. On the contrary, good reproductive phase mobiliza-
tion of Mn to grains at harvest stage with an increased
spike Mn concentration (along with flag leaf) accompanied
by decreased Mn concentration in the other plant parts
including older leaves has been reported recently in barley
by Birsin et al. (2010). Mn moves readily from roots, stems
and petioles to developing sinks, including seeds in lupin
(Hannam et al. 1985). Under Mn deficiency, Mn content of
stem, peduncle and flag leaf decreases and that of glumes
increases towards maturity (Pearson and Rengel 1994).
Sharp decline of mineral nutrient content from vegetative
organs during reproductive growth stage occurs because
nutrient uptake generally decreases, mainly as a result of
decreasing carbohydrate supply to the roots (Marschner
1995). So, the citied literature suggests that the higher
yield of efficient cultivars under Mn deficiency may be
related to superior Mn partitioning to grain and lesser
retention of Mn in the vegetative parts. On this hypothesis,
we assessed the organ-specific changes in dry matter and
Mn uptake to monitor the Mn dynamics between source
(leaves, L and tiller, T) and sink (panicle, P and grain, G)
during reproductive development i.e., from anthesis to
maturity.
Plant Cell Rep
123
Materials and methods
Experimental design and plant sampling
A greenhouse experiment was conducted at the Punjab
Agricultural University, Ludhiana, India (30�560N, 75�320Eand 247 m above MSL) to understand the influence of
source sink relationship on differential Mn efficiency of
four diverse rice genotypes. These genotypes were cate-
gorized into Mn efficient (PR 116, PR113) and Mn inef-
ficient (PR 111, PR115) on the basis of relative grain yield
and Mn uptake determined by Jhanji et al. (2012).
Manganese deficient soil samples were collected from
Mn deficient field (0–15 cm) in Bhatha Dhua, Ludhiana.
The soil was loamy sand (85 % sand, 6 % silt and 9 %
clay) of great group Ustochrepts with bulk density
1.53 g cm-3, pH 8.3, 6 % CaCO3, 0.6 g kg-1 soil organic
C and 1.54 mg kg-1 soil DTPA-extractable Mn. A basal
dose of 120 mg N through urea, 13 mg P through KH2PO4
and 25 mg K through KCl kg-1 soil was applied to all the
pots. Five healthy 30-day old seedlings of 4 rice genotypes
were transplanted in plastic pots filled with 9 kg of Mn
deficient soil.
The treatments consisted of two Mn levels viz. low Mn
(no Mn fertilizer, 0 ppm) and high Mn (50 mg Mn kg-1
soil applied as MnSO4�H20) and five stages of grain
development (from 7DAA to 35 DAA/maturity). A com-
pletely randomized design was used in a factorial
arrangement of the eighty pots, where each treatment was
replicated ten times. Ten plants were collected at a weekly
interval from 7 days after anthesis (DAA) to maturity.
Sample analyses for different parameters
Following morphophysiological parameters were recorded
at 7 DAA and 21 DAA:
SPAD index of 10 leaf samples was recorded using
SPAD 502. Maximum length and width of the subsidiary
leaves and the flag leaf were recorded and leaf area was
calculated by multiplying leaf length and width with a
constant (0.83) for rice leaf. Nitrate reductase activity
(NRA, l moles KNO3 reduced g-1 fresh weight h-1) of
fresh leaf segments was estimated by in vivo method of
Jaworski (1971).
At each stage of grain development, the plants were
separated into leaves, tillers, panicles and grains. The leaf
and tiller together constituted the source and the panicle
and grain, sink. Different plant parts were dried in an oven
at 60 �C up to a constant dry weight and then their weights
were recorded.
The dried plant parts were then milled. Ground material
was digested with 2:1 mixture of nitric (HNO3) and per-
chloric acid (HClO4) and analyzed for manganese
concentration (ppm) by atomic absorption spectroscopy
(Isaac and Kerber 1971) using atomic absorption spectro-
photometer Model A A 240 F S, Company 96 Varian,
Germany.
Calculations
The following parameters were then calculated:
1. Manganese uptake in grain (lg/plant) = grain yield
(g/plant) 9 grain Mn content (lg/g) (Graham 1984).
2. Manganese efficiency index = grain yield at low Mn/
grain yield at high Mn 9 100 (relative yield).
3. Manganese efficiency = grain Mn uptake at low Mn/
grain Mn uptake at high Mn 9 100 (relative Mn
uptake).
4. Dry matter partitioning of individual organ = dry
weight of the organ/total shoot dry weight 9 100.
5. Manganese uptake partitioning of individual
organ = Mn uptake in the organ/total Mn uptake.
6. Partitioning Quotient (PQ) = Per cent Mn uptake in
an organ/per cent dry weight of organ 9 100 (Waters
and Grusak 2008).
7. Dry matter translocation = Dry matter at anthesis -
dry matter at maturity.
8. Dry matter translocation efficiency = Dry matter
translocation/dry matter at anthesis x 100.
9. Dry matter accumulation = Dry matter at maturity -
dry matter at anthesis.
10. Dry matter accumulation efficiency = Dry matter
accumulation/dry matter at maturity x 100.
11. Contribution of pre-anthesis assimilates to the grain
weight = Dry matter translocation/grain weight at
maturity.
Statistical analyses
The data were subjected to analysis of variance (ANOVA)
appropriate for completely randomized design to evaluate
difference between the treatment means. Least significant
difference (LSD) was used for all comparisons where
significant F-probabilities (P B 0.05) were found. Standard
error of mean for each treatment was calculated. Correla-
tion coefficient between yield and morphophysiological
parameters was worked out (Singh et al. 2001).
Results
The results indicated that Mn deficiency decreased the
grain yield in all genotypes but the efficient genotypes were
affected to a lesser extent than inefficient genotypes. The
differential Mn efficiency of genotypes was due to
Plant Cell Rep
123
difference in dry matter and Mn uptake partitioning
between source and sink.
Analysis of variance
The data pertaining to dry matter accumulation at different
stages of grain development in four rice genotypes at two
Mn levels were subjected to analysis of variance (Table 1).
The total dry matter, dry matter accumulation in leaf, tiller,
panicle and grain varied significantly with stage of devel-
opment, genotype and Mn level except panicle in which no
significant variation between genotypes for dry matter
accumulation was observed and leaf where dry matter
accumulation was independent of Mn level.
Grain yield
The grain yield increased significantly in all genotypes
with Mn application. Under low Mn, the efficient
genotypes, PR 116 and PR 113 retained 87 and 81 %,
respectively, of the grain yield at adequate Mn, whereas the
corresponding values for inefficient genotypes, PR 115 and
PR 111 were 65 and 75 %, respectively (Fig. 1).
To unravel the mechanism of differential Mn efficiency in
these genotypes source sink relationship in terms of dry matter
accumulation and Mn uptake during grain filling period was
studied. A genotype showed similar accumulation pattern at
low and high Mn with only difference in absolute values
(Table 2). Thus, for better understanding of the mechanism,
the data from the low Mn treatment are explained.
Dry matter accumulation
The dry matter accumulation in different plant parts (leaf,
tiller, panicle and grain) was recorded at weekly interval
during grain filling period. Dry matter accumulation sig-
nificantly decreased in leaf and tiller (source) throughout
grain filling period in all genotypes (Fig. 2). The highest
decline in leaf dry weight was 28 % for PR 116 during
grain filling period, whereas least for PR 113 (7 %,
Table 2). The tiller dry weight declined by 32 % in PR
113, whereas by 13 % in PR 116. The inefficient geno-
types showed reduction in leaf dry weight by 23 % (PR
115) and 25 % (PR 111), whereas no changes were
observed for their tiller dry weight during grain filling
period (Table 1).
The dry matter accumulation in panicle and grain (sink)
increased during grain filling period in all genotypes
(Fig. 2). An increase of about two folds in panicle dry
weight was observed for PR 115 and PR 111(inefficient),
whereas increase was 17 and 68 %, respectively, for PR
116 and PR 113 during grain filling period. The accumu-
lation of dry weight in grain was higher for efficient
genotypes (PR 116 and PR 113) than inefficient genotypes
(PR 115 and PR 111). The dry matter mobilized from
source to developing sink up to 21 DAA in efficient
genotypes, whereas up to 14 DAA in inefficient genotypes.
The source (L & T) in PR 116 and PR 113, respectively,
contributed about 20 and 23 % dry weight to grain
throughout grain development in comparison to 11 and
Table 1 Analysis of variance
for total dry matter (g/plant),
dry matter in leaf, tiller, panicle
and grain (g) at different stages
of grain development growing
at two Mn levels
No. of replications = 3
Parameter Factor Total dry matter Leaf Tiller Panicle Grain
LSD (5 %) Stage of development (S) 0.54 0.24 0.26 0.59 0.42
Genotype (G) 0.48 0.22 0.24 NS 0.37
S 9 G NS 0.49 0.53 NS 0.83
Mn level (M) 0.34 NS 0.17 0.38 0.26
S 9 M NS 0.34 0.37 0.84 0.59
G 9 M 0.68 0.31 0.33 0.75 NS
S 9 G 9 M NS 0.69 NS NS NS
CV (%) 5.09 11.23 8.94 10.16 10.66
Bc
Bb Bb
Ba
Ac
Ab
Aa
Aa
0.0
2.0
4.0
6.0
8.0
10.0
12.0
14.0
16.0
PR 116 (87) PR 113(81) PR 115(65) PR 111(75)
Gra
in y
ield
(g
/pla
nt)
Genotypes
High Mn Low Mn
Fig. 1 Grain yield (g/plant) of four diverse rice genotypes under
different Mn levels. Values in the parentheses on X-axis represent Mn
efficiency index. Different upper case letters indicate statistically
significant differences between mean of the grain yield at low and
high Mn supply in a genotype and different lower case letters indicate
significant differences between mean of the grain yield of different
genotypes at high or low Mn level (P \ 0.05)
Plant Cell Rep
123
7 % by PR 115 and PR 111, respectively (Fig. 3). The
contribution of preanthesis assimimilates from source to
sink was least for PR 115 (33 %) and PR 111 (34 %) and
highest for PR 113 (44 %, Table 3). The contribution of
dry weight from source and panicle together to grain
decreased to 15 and 6 % in PR 116 and PR 113, respec-
tively, indicating that panicle hinders the mobilization to
grain. The dry weight of source and panicle in PR115 and
PR 111 increased during grain development by 15 and
12 %, respectively, indicating that the source was mobi-
lizing dry weight to developing sink but panicle was
accumulating dry weight instead of mobilizing it to grain.
The results pertaining to differential source–sink parti-
tioning of dry weight at maturity in efficient and inefficient
genotypes are presented in Fig. 4. The grain in efficient
genotypes accumulated 49 % (PR 116) and 46 % (PR 113)
of total dry weight per plant at maturity, whereas the
inefficient genotypes accumulated 35 % (PR 115) and
33 % (PR 111) of total dry weight in grain. The panicle of
PR 116, PR 113, PR 115 and PR 111, respectively, accu-
mulated 10, 18, 21 and 19 % of total dry matter and the
corresponding values for tiller were 23, 17, 26, and 29 %.
The leaf in all genotypes accumulated about 16–17 % of
total dry matter. Thus, among the vegetative parts, PR 116
accumulated highest dry matter in tiller, PR 113 almost
same in the leaf, tiller and panicle, whereas PR 115 and PR
111 in tiller.
Mn uptake
The Mn uptake was recorded at weekly interval during
grain filling period. The uptake of Mn decreased in source
during grain filling period to support developing sink
(Table 4; Fig. 5). The Mn uptake in leaf of PR 116 and
PR 113, respectively, decreased by 24 and 14 % from
anthesis to maturity i.e., during grain development,
whereas the corresponding values were 2 and 8 %,
respectively, for PR115 and PR 111. The highest decrease
in tiller dry weight during grain development was
observed in PR 113 (54 %) followed by PR 116 (31 %),
PR 115 (34 %), and PR 111 (8 %). During grain devel-
opment, Mn uptake increased in both panicle and grain.
The Mn uptake in panicle increased by 64 % in both
efficient genotypes, whereas 78 % in PR 115 and 75 % in
PR 111. The Mn uptake increased by 85 and 83 %,
respectively, in grain of PR116 and PR 113 during grain
filling period, whereas in inefficient genotypes, PR 115
and PR 111, the corresponding values were 73 and 67 %,
respectively (Table 4).
The contribution of source to Mn uptake in grain was
32 % in PR 113, 27 % in PR 116, 19 % in PR 115, and
12 % in PR 111 during grain development (Fig. 6). The
contribution of source and panicle to Mn uptake in devel-
oping grain decreased to 15 and 13 %, respectively, in PR
116 and PR 113, whereas the total uptake in source and
Table 2 Dry matter (g/plant)
partitioning in different plant
parts of four rice genotypes
during grain filling period under
different Mn supply
Stage of
development
Cultivar Low Mn High Mn
Leaf Tiller Panicle Grain Total Leaf Tiller Panicle Grain Total
7 DAA PR116 4.98 5.91 1.91 1.36 14.15 6.42 6.73 3.25 1.78 18.18
PR113 3.72 4.94 2.07 0.92 11.65 5.52 6.92 2.76 1.01 16.21
PR115 4.21 5.19 1.28 0.85 11.53 3.74 5.51 2.26 0.93 12.45
PR111 4.44 5.00 1.40 0.93 11.76 3.76 5.34 1.87 0.93 11.90
14 DAA PR116 4.19 5.98 1.81 7.29 19.27 5.15 6.32 2.632 7.51 21.61
PR113 3.88 4.40 2.83 5.93 17.04 4.40 4.59 1.803 8.18 18.98
PR115 4.05 5.29 2.48 5.80 17.62 3.66 5.52 1.903 6.94 18.03
PR111 3.77 5.69 2.34 4.34 16.14 3.71 5.55 2.545 5.82 17.62
21 DAA PR116 3.83 5.57 1.79 9.41 20.60 3.42 5.68 2.405 11.30 22.81
PR113 3.31 3.50 3.83 7.03 17.68 3.51 3.81 3.444 9.30 20.06
PR115 3.90 5.36 4.26 5.31 18.83 3.52 5.44 2.274 8.14 19.37
PR111 3.59 5.56 3.04 4.72 16.91 3.64 5.28 1.729 7.16 19.14
28 DAA PR116 3.63 5.32 2.28 10.60 21.83 3.27 5.27 3.029 12.56 24.13
PR113 3.50 3.35 3.45 8.53 18.83 3.00 3.53 2.470 10.81 19.82
PR115 3.38 5.13 4.00 6.80 19.31 2.73 5.21 1.433 10.40 19.78
PR111 3.44 5.39 3.68 5.81 18.32 3.53 5.19 1.840 8.29 20.18
Maturity PR116 3.56 5.14 2.24 10.88 21.82 3.24 5.29 3.419 12.50 24.45
PR113 3.43 3.34 3.47 8.91 19.16 3.02 3.39 2.470 11.01 20.89
PR115 3.25 5.14 4.16 6.84 19.39 2.63 5.15 1.590 10.48 19.85
PR111 3.32 5.42 3.60 6.25 18.59 3.51 5.10 2.102 8.36 19.41
Plant Cell Rep
123
*
*
*
2.5
3
3.5
4
4.5
5
5.5
5.5
Lea
f D
ry W
eig
ht(
g/p
lan
t)
APR116 PR113
PR115 PR111
*
*
*
2.5
3
3.5
4
4.5
5
5.5
6
6.5
7
7.5
Till
er D
ry W
eig
ht(
g/p
lan
t) B
**
*
*
*
*
*
*
1
1.5
2
2.5
3
3.5
4
4.5
5
7 14 21 28 Maturity
Pan
icle
Dry
Wei
gh
t(g
/pla
nt)
Days after anthesis
C
*
*
*
**
*
* *
*
* *
0
1
2
3
4
5
6
7
8
9
10
11
7 14 21 28 Maturity
Gra
in D
ry W
eig
ht(
g/p
lan
t)
Days after anthesis
D
Fig. 2 The dry weight of the (a) leaf, (b) tiller, (c) panicle and
(d) grain of four diverse rice genotypes at different stages of grain
development. The bars indicate the LSD (P B 0.05) between the
genotypes at each stage of development/harvest, otherwise not
significantly different. Asterisks indicate differences (P B 0.05) from
previous stage of development in a genotype, otherwise not signif-
icantly different
-20
-25
-11
-7
-15
-6
1512
-30
-25
-20
-15
-10
-5
0
5
10
15
20
PR116 PR113 PR115 PR111
Per
cen
t d
ry w
eig
ht
source
source+panicle
Fig. 3 Differential contribution of dry weight from source and
panicle to grain at maturity by four diverse rice genotypes under low
Mn
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
PR116 PR113 PR115 PR111Per
cen
t p
arti
tio
nin
g o
f d
ry w
eig
ht
at m
atu
rity
leaf tiller panicle grain
Fig. 4 Partitioning of dry weight in various plant parts of four
diverse rice genotypes at maturity under low Mn
Plant Cell Rep
123
panicle increased by 3 and 6 %, respectively, for PR 115
and PR 111 indicating that towards maturity the panicle
might be accumulating Mn in itself instead of mobilizing it
to grain.
The results pertaining to differential source–sink parti-
tioning of Mn uptake at maturity in efficient and inefficient
genotypes are presented in Fig. 7. At maturity, the source
in PR 113 had 64 % of total Mn uptake and sink had 36 %,
whereas corresponding values for Mn uptake were 72 and
28 %, respectively, in PR 116; 71 and 29 % in PR115 and
74 and 26 % in PR 111. Out of 36 % of total Mn uptake in
sink of PR 113, 27 % was in panicle and only 9 % in grain.
In PR 116, out of 28 % of total Mn uptake in sink, 16 %
was in panicle and 12 % in grain. The corresponding val-
ues for PR 115 and PR 111 were, respectively, 29 and
26 % in sink, 23 and 21 % in panicle and 6 and 5 % in
grain (Fig. 7). The translocation index i.e., uptake in grain/
total uptake in shoot was 0.12 in PR 116 and 0.05 in PR
111. The uptake partitioning revealed that source of all
genotypes mobilized the Mn towards the sink to almost
same extent but it was the panicle that immobilised Mn.
The highest per cent Mn uptake in panicle was in PR113
and lowest in PR 116. The lowest percent uptake in panicle
of PR 116 revealed that it supported developing grain to
have highest translocation index.
Partition quotient (PQ)
Partition quotient values were calculated to check the
concentration of Mn in an organ irrespective of the dry
matter or size of that organ. The leaf, tiller, panicle, and
grain of efficient genotype, PR 116, respectively, had
highest PQ values of 262, 123, 163, and 23 than inefficient
genotype, PR111 where corresponding values were 230,
114, 107, and 14 (Fig. 8). A significant and positive cor-
relation was found between Mn concentration in a part and
its dry matter (r = 0.87**).
Nitrate reductase activity
The highest NR activity of 0.15 and 0.18 was recorded in
leaf and panicle of PR 116, whereas least in PR111 (0.03 in
leaf and 0.05 in panicle) at 7 DAA (Fig. 9). The corre-
sponding values at 21 DAA were 0.07 in both leaf and
panicle of PR 116, and 0.01 and 0.05, respectively, in leaf
and panicle of PR 111.
*
*
*
**
*
*
*
*
**
*
603
633
663
693
723
753
783
813
843
873
903
933
Lea
f u
pta
ke(µ
g/p
lan
t)
A PR116 PR113
PR115 PR111
**
**
*
* *
*
*
203
253
303
353
403
453
503
553
603
653
703
753
803
Till
er u
pta
ke(µ
g/p
lan
t)
B
**
**
*
**
*
*
*
*
*
*
*
**
1
51
101
151
201
251
301
351
401
451
7 14 21 28 Maturity
Pan
icle
up
take
(µg
/pla
nt)
Days after anthesis
C
*
**
*
**
** *
**
**
0
20
40
60
80
100
120
140
160
180
200
7 14 21 28 Maturity
Gra
in u
pta
ke(µ
g/p
lan
t)
Days after anthesis
D
Fig. 5 The Mn uptake in the a leaf, b tiller, c panicle and d grain of
four diverse rice genotypes at different stages of grain development.
The bars indicate the LSD (P B 0.05) between the genotypes at each
stage of development/harvest, otherwise not significantly different.
Asterisks indicate differences (P B 0.05) from previous stage of
development in a genotype, otherwise not significantly different
Plant Cell Rep
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Leaf area and flag leaf area
The total leaf area of inefficient genotypes, PR 115
(177 dm2) and PR 111 (217 dm2), was higher than efficient
genotypes, PR116 (129 dm2) and PR 113 (143 dm2) but
flag leaf area was highest for PR 116 (1,712 dm2) at 7
DAA (Fig. 10). At 21 DAA, the total leaf area declined in
all genotypes but flag leaf area which is the photosyn-
thetically active source increased in all genotypes. The flag
leaf area of PR 116, PR113, PR 115, and PR 111 con-
tributed to about 15, 5, 4, and 4 % of the total leaf area at
21 DAA. Thus, the photosynthetically active source was
more active in efficient genotypes than inefficient
genotypes.
SPAD index
SPAD index measures the relative chlorophyll content.
There was no significant difference in the value of SPAD
index among different cultivars at 7 DAA and 21 DAA, but
PR 116 at 21 DAA retained 78 % of the SPAD value at 7
DAA, whereas the corresponding value was 60 % for PR
115 and PR 111 (Fig. 11).
The grain yield was significantly and positively corre-
lated to flag leaf area (r = 0.74**) and nitrate reductase
activity (NRA) in panicle (r = 0.76**) and NRA in flag
leaf (r = 0.79**). The leaf area (r = -0.75**) was sig-
nificantly but negatively correlated to grain yield. Thus,
efficient genotypes with higher flag leaf area as well as
NRA activity and lower total leaf area had higher yield in
comparison to inefficient genotypes.
Discussion
Manganese deficiency suppressed the grain yield in several
crop species (Abbas et al. 2011; Bansal and Nayyar 1998;
Jhanji et al. 2011). The reduced grain yield under Mn
deficiency could be explained by the role of Mn in cascades
of metabolic and physiological processes of growth and
development (Millaleo et al. 2010). The application of Mn
significantly increased the yield of all genotypes (Table 1),
suggesting the role of Mn in appropriate partitioning of
nutrients and assimilates between vegetative and repro-
ductive parts (Soylu et al. 2005). The efficient genotypes
PR116 (87 %) and PR113 (81 %) had higher Mn efficiency
index than inefficient genotypes, PR 115 (65 %) and
PR111 (75 %). A significant and positive correlation
between grain yield and Mn efficiency index (r = 0.91**)
supports our finding that genotype with high yield at low
Mn had high efficiency index. The results that efficient
genotypes had high Mn efficiency index i.e., retain high
grain yield under low Mn supply than inefficient genotypes
were in accordance to our previous studies related to field
screening of diverse rice (Jhanji et al. 2012) and wheat
(Jhanji et al. 2013a) genotypes.
Dry matter production of efficient genotypes was more
than inefficient genotypes at all stages during grain
development (Table 1). Higher dry matter production of
efficient genotypes than inefficient genotypes had been
reported earlier in rice (Jhanji et al. 2011) and wheat
(Jhanji et al. 2013b). Dry matter accumulation in a plant is
the product of cascades of metabolic processes, such as
photosynthesis, respiration, partitioning of assimilates;
internal factors, such as chlorophyll, carotene and other
pigment contents, capacity to store food reserves; genetic
factors providing resistance to climatic, edaphic and bio-
logical stresses, and environmental factors. The photosyn-
thetic efficiency of a plant determines the dry matter
production (Singal et al. 1992). Thus, higher dry matter
production in efficient genotypes might be due to higher
photochemical efficiency or lower Mn requirement. The
measures of photosynthetic efficiency viz. SPAD index and
NRA were higher in efficient genotypes. Higher NRA in
efficient genotypes indicates higher photochemical effi-
ciency because reduction of nitrate requires reducing
power i.e., NADPH generated by the photochemical reac-
tions as well as the activity of nitrate reductase enzyme.
Table 3 Dry matter related parameters of four rice genotypes under low Mn supply
Cultivar Dry matter
translocation
from source (g/
plant)
Dry matter
translocation
efficiency of
source (%)
Contribution of
pre-anthesis
assimilates to
sink (%)
Dry matter translocation
(?)/accumulation (-) in
source and panicle (g/
plant)
Dry matter translocation
(?)/accumulation (-)
efficiency of source and
panicle (%)
Contribution of
pre-anthesis
assimilates to
grain (%)
PR 116 4.1b 32b 38b ?1.86b ?14b ?17b
PR 113 4.0b 37c 44c ?0.49a ?4a ?5a
PR 115 2.3a 21a 33a -1.87B -17B -27B
PR 111 2.1a 19a 34a -1.5A -13A -24A
Different lower case letters indicate statistically significant differences between the genotypes for the mean of values in a column (P \ 0.05)
Different upper case letters indicate significant differences between the genotypes for the mean of values in a column (P \ 0.05). (Comparison of
treatment means with LSD; No. of replications = 3)
Plant Cell Rep
123
The NR activity was highest in leaf and panicle of efficient
genotype (PR 116) at both stages indicating high photo-
synthetic activity of source and developing sink supporting
high dry matter accumulation and grain yield. Low NR
activity of leaf of inefficient genotypes revealed that during
grain development, source becomes photosynthetically less
active and thus, contribution to developing grains reduces.
High NR activity of panicle than leaf indicates that panicle
itself remains photosynthetically active during grain
development for a longer time to support developing grain
in all genotypes but panicle of efficient genotypes showed
higher activity than inefficient genotype.
Flag leaves are the main photosynthetic tissues and the
photochemical efficiency also depends upon the area of
Table 4 Partitioning of Mn uptake (lg/plant) in different plant parts
of four rice genotypes during grain filling period under low Mn supply
Stage of
development
Cultivar Low Mn
Leaf Tiller Panicle Grain Total
7 DAA PR116 910 680 98 28 1,716
PR113 751 667 149 23 1,590
PR115 642 734 83 25 1,484
PR111 708 625 83 25 1,441
Mean 753 677 104 25 1,558
14 DAA PR116 774 632 112 132 1,650
PR113 871 538 191 98 1,698
PR115 695 666 203 132 1,696
PR111 676 588 148 92 1,504
Mean 754 606 164 114 1,638
21 DAA PR116 733 650 137 161 1,681
PR113 741 439 333 123 1,636
PR115 784 481 375 104 1,744
PR111 747 559 231 88 1,625
Mean 744 532 269 119 1,664
28 DAA PR116 715 598 244 175 1,732
PR113 724 328 361 120 1,533
PR115 679 432 343 118 1,572
PR111 714 539 304 104 1,661
Mean 708 474 313 129 1,625
Maturity PR116 693 472 271 188 1,624
PR113 647 306 409 135 1,497
PR115 631 486 372 91 1,580
PR111 651 527 329 75 1,582
Mean 656 448 345 122 1,572
LSD (0.05) S 18.8 9.9 7.4 5.6 28.1
G 16.9 8.9 6.6 5.0 25.1
S 9 G 37.7 19.8 14.8 11.3 56.2
CV (5 %) 3.16 2.19 3.75 6.70 2.11
Statistical analysis: two way ANOVA and comparison of treatment
means with LSD; No. of replications = 3
S stage of development, G genotype
-27
-32
-19
-12
-15-13
3
6
-35
-30
-25
-20
-15
-10
-5
0
5
10
PR116 PR113 PR115 PR111
Per
cen
t M
n u
pta
ke
source
source+panicle
Fig. 6 Differential contribution of Mn uptake from source and
panicle to grain at maturity by four diverse rice genotypes at low Mn
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
PR116 PR113 PR115 PR111Per
cen
t p
arti
tio
nin
g o
f M
n u
pta
ke a
t m
atu
rity leaf tiller panicle grain
Fig. 7 Partitioning of Mn uptake in various plant parts of four
diverse rice genotypes at maturity at low Mn
c
a
c
c
b
a
c
b
b
a b
ba
a
a a
a0
50
100
150
200
250
300
leaft tiller panicle grain
Par
titi
on
qu
oti
ent
(PQ
)
PR116 PR113 PR115 PR111
Fig. 8 Partition quotient of Mn in different plant parts of four diverse
rice genotypes at maturity. Different lower case letters indicate
significant differences between mean of PQ of a plant part of different
genotypes at maturity (P \ 0.05)
Plant Cell Rep
123
the photosynthetic tissue. The efficient genotypes had
higher flag leaf area than inefficient genotypes to support
the assimilate production. This supports our findings that
efficient genotypes contributed more to developing sink,
as the photosynthetically active source itself remains
active up to 21 DAA to a greater extent than in inefficient
genotypes.
The Mn uptake in a plant part is the product of dry
matter accumulation and concentration of Mn in that
part. Mn distribution from sources to sinks takes place
via phloem (Marschner 1995). and its redistribution
depends on the plant species and stages of development
(Herren and Feller 1994). Several transporter gene
families have been implicated in Mn2? transport,
including cation/H? antiporters, natural resistance-asso-
ciated macrophage protein (Nramp) transporters, zinc-
regulated transporter/iron-regulated transporter (ZRT/
IRT1)-related protein (ZIP) transporters, the cation dif-
fusion facilitator (CDF) transporter family, and P-type
ATPases (Ducic and Polle 2005; Pittman 2005). So, the
differential transport of Mn might be due to difference in
genetic inheritance of these transporters in efficient and
inefficient genotypes.
The results revealed similar trend in Mn uptake in
source and sink of efficient and inefficient genotypes as of
dry matter accumulation and translocation. Fageria et al.
(2008) reported that there are certain genotypes that can
Bb
Aa Ba Ba
Bc
BbBb
Aa
Ac
Bb
Aa Aa
Ac
AaAa Ab
0.00
0.02
0.04
0.06
0.08
0.10
0.12
0.14
0.16
0.18
0.20
PR116 PR113 PR115 PR111 PR116 PR113 PR115 PR111
PanicleLeaf
(µ m
ole
s o
f K
NO
3re
du
ced
/g f
resh
wt/
hr)
7 DAA 21 DAA
Fig. 9 The nitrate reductase
activity in leaf and panicle of
four diverse rice genotypes at 7
and 21 days after anthesis
(DAA). Different upper case
letters indicate statistically
significant differences between
mean of NRA at 7 and 21 DAA
in a genotype and different
lower case letters indicate
significant differences between
mean of NRA of different
genotypes at 7 or 21 DAA
(P \ 0.05)
75%
80%
85%
90%
95%
100%
7
DAA
21
DAA
7
DAA
21
DAA
7
DAA
21
DAA
7
DAA
21
DAA
PR116 PR113 PR115 PR111
Per
cen
t d
ry w
eig
ht
of
leaf
an
d
fla
g le
af p
er p
lan
t
Leaf Flag leaf
Fig. 10 The per cent of dry weight of flag leaf and other leaves out of
total leaf in a plant of four diverse rice genotypes at 7 and 21 DAA
A A A A0.0
5.0
10.0
15.0
20.0
25.0
30.0
35.0
40.0
45.0
c b a a
PR116 PR113 PR115 PR111
SP
AD
ind
ex7 DAA 21DAA
Fig. 11 The SPAD index in leaves of four diverse rice genotypes at 7
and 21 days after anthesis (DAA). Different upper case letters
indicate statistically significant differences between mean of SPAD
index of different genotypes at 7 DAA and different lower case letters
indicate significant differences between mean of SPAD index of
different genotypes at 21 DAA (P \ 0.05)
Plant Cell Rep
123
adapt to variable amounts of Mn and can be induced to
higher uptake of Mn under limiting conditions.
From anthesis to maturity, the dry matter production
decreased in the source of all genotypes (Fig. 2). The
loss of dry matter from source to sink during the grain
filling period was higher from efficient genotypes, sug-
gesting active transport of assimilates to the panicles
(Guindo et al. 1994). The dry matter production espe-
cially from 21 DAA to maturity in all genotypes showed
non-significant changes which could be explained par-
tially by the senescence of the lower leaves (Norman
et al. 1992). Fageria (2007) also reported reduction in
dry matter of upland rice from flowering to physiological
maturity.
The different response of efficient and inefficient
genotypes could be explained due to their differential
partitioning of dry matter between different plant parts.
The dry matter partitioning is the end result of a coor-
dinated set of transport and metabolic processes govern-
ing the flow of assimilates from source organs to the sink
organs (Marcelis 1996). The grain harvest index was 0.49
for PR 116 and 0.34 for PR111, explaining the higher
yield of PR 116 due to better partitioning of dry matter
towards grain. Dry matter translocation from source to
sink of PR116, PR 113, PR115, and PR111 was 4.1, 4.0,
2.3, and 2.1 g/plant. The dry matter translocation from
source and panicle’s vegetative parts to grain decreased to
1.86 and 0.49 g/plant, respectively, for PR 116 and PR
113, but for PR115 and PR 111 instead of translocation,
dry matter accumulated in source and panicle’s vegetative
parts by 1.87 and 1.5 g/plant, respectively. This clearly
revealed that in both efficient and inefficient genotypes,
the source (leaf and tiller) translocated dry matter to grain
although with different translocation efficiency (PR116,
PR 113, PR115, and PR111, respectively, had 32, 37, 21,
and 19 %) but it was the panicle in inefficient genotypes
that accumulated dry matter instead of translocating to
grain. Jiang and Ireland (2005) and Sperotto et al. (2012),
respectively, reported Zn and Fe translocation from veg-
etative parts to grain during reproductive development in
rice.
PQ values allow the comparison of partitioning of
mineral in different parts regardless of differences in dry
matter accumulation in the part. The high PQ values in
efficient genotypes than inefficient genotypes revealed
higher accumulation or uptake of Mn in different parts of
efficient genotypes even under low Mn supply. The higher
accumulation or uptake of Mn might be due to better root
growth of efficient genotypes (Shankar et al. 2013). The
efficient genotypes of rice (PR 116 and PR113) had longer
roots than inefficient genotypes (PR115 and PR 111; Jhanji
et al. 2011).
Conclusions
Mn efficiency of a genotype could be explained on the
basis of different uptake rates, root morphology, and dif-
ferential physiology or storage and translocation of the
nutrient (Marschner 1995). Thus, the results revealed that
the translocation of dry matter and Mn from source to sink
or vegetative parts to grain was higher in efficient geno-
types under low Mn than inefficient genotypes which
accounted for their higher efficiency.
Future research should target on the root uptake,
mechanism controlling distribution of Mn during vegeta-
tive growth and grain development, source efflux trans-
porters to increase Mn accumulation in sink and pathways
through which Mn enters the developing grain.
Contribution of Authors The planning and execution of
the experiment was done together. The co-author was
involved in compiling and analysis of data. Both the
authors contributed towards the writing of the manuscript.
Conflict of interest The authors declare that they have no conflict
of interest.
References
Abbas G, Khan MQ, Khan MJ, Tahir M, Ishaque M, Hussain F (2011)
Nutrient uptake, growth and yield of wheat (Triticum aestivum
L.) as affected by manganese application. Pak J Bot
43(1):607–616
Bansal RL, Nayyar VK (1998) Screening of wheat (Triticum
aestivum) varieties tolerant to manganese deficiency stress. Ind
J Agric Sci 68:66–69
Birsin MA, Adak MS, Inal A, Aksu A, Gunes A (2010) Mineral
element distribution and accumulation patterns within two barley
cultivars. J Plant Nutr 33(2):267–284
Dias AS, Lidon FC, Ramalho JC (2009) Heat stress in Triticum:
kinetics of Fe and Mn accumulation. Braz J Plant Physiol
21(2):153–164
Ducic T, Polle A (2005) Transport and detoxification of manganese
and copper in plants. Braz J Plant Physiol 17:103–112
Epstein E (1971) Mineral metabolism. In: Mineral nutrition of plants:
principles and perspectives, 1st edn. Wiley, New York,
pp 285–322
Fageria NK (2007) Yield physiology of rice. J Plant Nutr
30(6):843–879
Fageria NK, Barbosa MP, Filho A, Moreira A (2008) Screening
upland rice genotypes for manganese-use efficiency. Comm Soil
Sci Plant Anal 39:2873–2882
Fang Z, An Z, Li Y (2008) Dynamic change of organic acids secreted
from wheat roots in Mn deficiency. Front Agric China 2:50–54
Graham RD (1984) Breeding for nutritional characteristics in cereals.
In: Tinker PB, Lauchli A (eds) Advances in plant nutrition.
Praeger Publishers, New York, pp 57–102
Guindo D, Wells BR, Norman RJ (1994) Cultivar and nitrogen rate
influence on nitrogen uptake and partitioning in rice. Soil Sci Soc
Am J 58:840–845
Plant Cell Rep
123
Hannam RJ, Graham RD, Riggs JL (1985) Redistribution of
manganese in maturing Lupinus angustifolius cv. Illyarrie in
relation to levels of previous accumulation. Ann Bot
56(6):821–834
Herren T, Feller U (1994) Transfer of zinc from xylem to phloem in
the peduncle of wheat. J Plant Nutr 17:1587–1598
Hocking PJ, Pate JS, Wee SC, McCoomb AJ (1977) Manganese
nutrition of Lupinus spp. especially in relation to developing
seed. Ann Bot 41(4):677–688
Isaac RA, Kerber JD (1971) Atomic absorption and flame photom-
etry: techniques and uses in soil, plant and water analysis. In:
Walsh LM (ed) Instrumental methods for analysis of soil and
plant tissue. Soil Science Society of America, Madison,
pp 17–37
Jaworski EG (1971) Nitrate reductase assay in intact plant tissues.
Biochem Biophys Res Commun 43(6):1274–1279
Jhanji S, Sekhon NK, Sadana US, Gill TPS (2011) Characterization of
morphophysiological traits of rice genotypes with diverse
manganese efficiency. Ind J Plant Physiol 16(3&4):245–257
Jhanji S, Sadana US, Sekhon NK, Gill TPS, Khurana MPS, Kaur R
(2012) Screening diverse rice (Oryza sativa L.) genotypes for
manganese efficiency. Proc Natl Acad Sci India Sect B Biol Sci
82(3):447–452
Jhanji S, Sadana US, Sekhon NK, Khurana MPS, Sharma A, Shukla
AK (2013a) Screening diverse wheat genotypes for manganese
efficiency based on high yield and uptake efficiency. Field Crops
Res 154:127–132
Jhanji S, Sekhon NK, Sadana US, Sharma A, Shukla AK (2013b)
Evaluation of different Mn efficiency indices and their relation to
morphophysiological traits in diverse wheat genotypes. J Plant
Nutr (in press)
Jiang WZ, Ireland CR (2005) Characterization of manganese use
efficiency in U K wheat cultivars grown in a solution culture
system and in the field. J Agri Sci 143:151–160
Khoshgoftarmanesh AH, Schulin R, Chaney RL, Daneshbakhsh B,
Afyuni M (2010) Micronutrient-efficient genotypes for crop
yield and nutritional quality in sustainable agriculture: a review.
Agron Sustain Dev 30:83–107
Marcelis LFM (1996) Sink strength as a determinant of dry matter
partitioning in the whole plant. J Exp Bot 47:1281–1291
Marschner H (1995) Mineral nutrition of higher plants, 2nd edn.
Academic, London
Millaleo R, Reyes-Dıaz M, Ivanov AG, Mora ML, Alberdi M (2010)
Manganese as essential and toxic element for plants: transport,
accumulation and resistance mechanisms. J Soil Sci Plant Nutr
10(4):476–494
Norman RJ, Guindo D, Wells BR, Wilson CE (1992) Seasonal
accumulation and partitioning of nitrogen-15 in rice. Soil Sci Soc
Am J 56:1521–1527
Pearson J, Rengel Z (1994) Distribution and remobilization of Zn and
Mn during grain development in wheat. J Exp Bot 45:1829–1835
Pearson JN, Rengel Z, Jenner CF, Graham RD (1996) Manipulation
of xylem transport affects Zn and Mn transport into developing
wheat grains of cultured ears. Physiol Plant 98(2):229–234
Pittman J (2005) Managing the manganese: molecular mechanisms of
manganese transport and homeostasis. New Phytol 167:733–742
Riesen O, Feller U (2005) Redistribution of nickel, cobalt, manga-
nese, zinc, and cadmium via the phloem in young and maturing
wheat. J Plant Nutr 28(3):421–430
Sadana US, Lata K, Claassen N (2002) Manganese efficiency of
wheat cultivars as related to root growth and internal manganese
requirement. J Plant Nutr 25(12):2677–2688
Sadana US, Sharma P, Castaneda ON, Samal D, Claassen N (2005)
Manganese uptake and Mn efficiency of wheat cultivars are
related to Mn-uptake kinetics and root growth. J Plant Nutr
168:581–589
Shankar A, Sadana US, Jhanji S (2013) Mechanisms of differential
manganese uptake efficiency in winter cereals at generative
phase. Proc Natl Acad Sci India Sect B Biol Sci 83:525–531
Singal HR, Sheoran JS, Singh R (1992) Photosynthetic contribution
of pods towards seed yield in Brassica. Proc Ind Nat Sci Acad
58:365–370
Singh S, Bansal ML, Singh TP, Kumar R (2001) Statistical methods
for research workers. Kalyani Publishers, New Delhi
Soylu S, Sade B, Topal A, Akgun N, Gezgin S (2005) Responses of
irrigated durum and bread wheat cultivars to boron application in
low boron calcareous soil. Turk J Agri 29:275–286
Sperotto RA, Vasconcelos MW, Grusak MA, Fett JP (2012) Effects of
different Fe supplies on mineral partitioning and remobilization
during the reproductive development of rice (Oryza sativa L.).
Plant Soil 5:1–27
Waters BM, Grusak MA (2008) Whole plant mineral partitioning
throughout the life cycle in Arabidopsis Thaliana ecotypes
Coloumbia, Landsbergerecta, Cape verde islands, and the mutant
line ys/1ys/3. New Phytol 177:389–405
Wu CY, Lu LL, Yang XE, Feng Y, Wei YY, Hao HL, Stoffella PJ, He
ZL (2010) Uptake, translocation, and remobilization of Zinc
absorbed at different growth stages by rice genotypes of different
Zn densities. J Agric Food Chem 58:6767–6773
Yang XE, Chen WR, Feng Y (2007) Improving human micronutrient
nutrition through biofortification in the soil–plant system: China
as a case study. Environ Geochem Health 29(5):413–428
Yoneyama T, Gosho T, Kato M, Goto S, Hayashi H (2010) Xylem
and phloem transport of Cd, Zn and Fe into grains of rice plants
(Oryza sativa L.) grown in continuously flooded Cd-contami-
nated soil. Soil Sci Plant Nutr 56:445–453
Plant Cell Rep
123