American Journal of Plant Sciences, 2011, 2, 601-608
doi:10.4236/ajps.2011.24071 Published Online October 2011 (http://www.SciRP.org/journal/ajps)
601
Low Magnesium with High Potassium Supply
Changes Sugar Partitioning and Root Growth
Pattern Prior to Visible Magnesium Deficiency in
Leaves of Rice (Oryza sativa L.)
Yuchuan Ding1*, Guohua Xu2
1Institute of Agricultural Environment and Resources, Shanxi Academy of Agricultural Sciences, Taiyuan, China; 2College of Re-
sources and Environmental Sciences, Nanjing Agricultural University, Nanjing, China.
Received July 23th, 2011; revised September 8th, 2011; accepted September 20th, 2011.
ABSTRACT
This research was conducted to investigate the effects of low magnesium (Mg) with high potassium (K) supply on the
Mg concentration, sugar partitioning and root growth of rice (Oryza Sativa L. cv. Wuyunjing 7) plants grown in hy-
droponics under greenhouse conditions, at Nanjing Agricultural University, China. The nutrient solution contained
0.01 and 1.0 mM Mg concentration, with K at 1.0 and 6.0 mM. Compared with the co n trol (1mM Mg and K) treatment,
the soluble sugar content at the treatment of low Mg (0.01 mM) with high K (6 mM) decreased by 35.7% in leaves,
whereas increased 29.2% in roots at day 15 after treatment initiation. The shoot dry weight (DW) declined 12.9%, but
root DW increased 12.1% lead ing to the significan t increase in the ro ot to shoot ratio at da y 30. Furthermore, the total
root length, total root surface area, root volume, average root diameter, total length of 0 - 0.5 mm and 0.5 - 1.0 mm
diameter roots at day 30 significantly increased by 11.8%, 16.4%, 25.3%, 8.1%, 16.6% and 12.5%, respectively. Cor-
relation analysis revealed the root to shoot ratio is closely related to the soluble sugar contents in roots and root mor-
phological parameters of rice at day 15 and day 30. The typical visible symptoms of Mg deficiency in leaves of rice
were obtained in the trea tment of low Mg with high K at day 35. These findings indicated that low Mg with high K sup-
ply altered sugar pa rtition ing and roo t morpho logica l pa rameters, resultin g in th e in crea sed root to sho o t ra tio pr io r to
visible Mg deficiency symptoms in rice leaves. The increase in root to shoot ratio maybe an important adaptive mecha-
nism for rice plants to respond to low-Mg stress during the early growth stag e.
Keywords: Magnesium, Potassium, Sugar Partitioning, Root Growth Parameter, Rice
1. Introduction
Magnesium (Mg) is one of the essential mineral nutrients
for the growth and development of plants. Apart from
being a central atom of the chlorophyll molecule, Mg
also acts as activator or regulator of many key enzymes
in plant physiological processes [1,2]. Both Mg defi-
ciency and oversupply have detrimental effects on plant
photosynthesis [3], consequently resulting in abnormal or
restricted growth of plants [2].
With the introduction of high-yielding varieties, the
heavy application of nitrogen (N), phosphorus (P) and
potassium (K) fertilizers, the amplified rotations per site
and the continuous intensive harvesting of crop produc-
tions without recycling crop residues or replacing with
mineral fertilizers, the Mg depletion in soils is increasing
[4]. Consequently, many light-textured soils have been
shown to exhibit Mg deficiencies, particularly in highly
weathered acid soils with high percolation rates and
leaching losses. Mg deficiency can be caused not only by
small concentrations of the nutrient in a soil but also by
ionic antagonism, particularly in acid and K-rich soils.
The cation competitive effects frequently lead to Mg
deficiency in the field [5]. Mg deficiency in plants occurs
worldwide influencing productivity and quality in agri-
culture [4].
Plant growth and development depend highly on envi-
ronmental conditions, such as temperature, light intensity
and availability of water and essential mineral nutrients

Low Magnesium with High Potassium Supply Changes Sugar Partitioning and Root Growth Pattern Prior
602
to Visible Magnesium Deficiency in Leaves of Rice (Oryza sativa L.)
[6]. Mineral nutrients possess several roles in formation,
partitioning, and utilization of photosynthates. Therefore,
mineral nutrient deficiencies substantially impair produc-
tion of dry matter and its partitioning between the plant
organs [7]. Mg deficiency has been reported to affect
plant growth and biomass partitioning between root and
shoot [4]. Under Mg deficiencies root growth markedly
decreased, leading to an increase in shoot to root dry
weight (DW) ratios in plants [8-11].
Despite numerous studies examining the effects of Mg
deficiency on plant development and biomass allocation,
very little information is known about the influence of
Mg stress on plant biomass allocation before the symp-
toms of Mg deficiency appear in leaves of plants, espe-
cially in field crops. The present investigation was im-
plemented to study the interaction between Mg and K in
relation to their effects on the uptake and translocation of
Mg, soluble sugar partitioning and root growth parame-
ters during the early growth stage of rice (Oryza sativa
L.), one of the most important food crops for large world
population [12]. In this study, we found that under Mg
stress induced by low Mg with high K supply, rice
changes its soluble sugar partitioning and root growth
parameters leading to an increase in root to shoot DW
ratio before visible Mg deficiency symptoms occur in the
leaves of rice plants. With increasing Mg deficiency, the
root to shoot ratio was gradually decline, mainly because
of impaired photosynthesis and export of carbohydrates
from the leaves to roots of rice.
2. Materials and Methods
2.1. Plant Material and Cultivation
Rice (Oryza sativa L. cv. Wuyunjing-7) plants were
grown in hydroponics culture under greenhouse condi-
tions at Nanjing Agricultural University, Nanjing, China.
The maximum light intensities at the experimental site
ranged from 1100 to 1450 µmol·m–2·s–1 at 12:00 noon,
maximum and minimum temperature during this period
ranged 30˚C - 35˚C at daytime and 20˚C - 22.5˚C at night.
The relative humidity ranged from 65% to 75%. Seeds of
rice were washed thoroughly and disinfected in 10%
H2O2 for 20 min followed by five washes with deionized
water. Seeds of uniform size were imbibed overnight and
germinated in a solution in a plastic box in a growth
chamber (16 h light/8 h dark, day/night temperature of
28/22˚C, and 65% - 70% relative humidity). The uniform
20d-old seedlings (two-leaf stage) were transplanted into
a 5 L plastic container. The box had 12 holes in the lid
(two seedlings per hole). The transplanted rice seedlings
had been grown at one-fifth strength of full nutrient solu-
tion for two weeks prior to the beginning of the treat-
ments. The nutrient solusion, based on Yoshida et al.,
1972 [13], contained nutrients at the following concen-
trations (in µM): 1000 (NH4)2SO4; 1000 Ca(NO3)2; 1000
NaH2PO4; 1000 MgSO4·7H2O; 1000 KCl; 2000 Na2-
SiO3·9H2O; 0.5 MnSO4·H2O; 10.0 H3BO3; 1.0 Zn-
SO4·7H2O; 0.1 CuSO4·5H2O; 0.05 (NH4)6Mo7-O24·4H2O;
20.0 FeNaEDTA. All nutrients were made with the AR
grade salts in deionized water. The average pH of the
solutions was daily controlled and maintained at 5.8 ±
0.1. The deionized water was added to the container daily
to replace water loss by transpiration. The nutrient solu-
tions were replaced every three days. The electrical con-
ductivity (EC) of the nutrient solution was maintained
below 2.0 dS·m–1. At the beginning of the third week
after transplanting, the concentrations of Mg and K in the
culture solutions were adjusted to: 0.01 (low level) and
1.0 mM (normal level as control) of Mg and to: 1.0
(normal level) and 6.0 mM (high level) of K, for a total
of four treatments (Mg0.01K1, Mg0.01K6, Mg1K1, Mg1K6).
Each treatment was replicated three times in a com-
pletely randomized design (CRD).
2.2. Chemical Analysis of Plant Tissue
Plants were harvested at day 15 (seven-leaf stage), 30
(nine-leaf stage) and 40 (eleven-leaf stage) after treat-
ment initiation. At each harvest, the plants were divided
into shoots and roots. The roots were washed by tap wa-
ter and cleaned with distilled water. The plant material
for determination of dry weight and mineral analysis was
dried in a forced air oven for 48 h at 70˚C. K concentra-
tions were determined by flame emission photometry
(FEP). Mg concentrations were assayed by atomic ab-
sorption spectrometry (AAS) after wet digestion in a
block digester using an H2SO4-H2O2 solution [14].
2.3. Measurement of Root Morphological
Parameters
At each harvest, root samples were scanned using the
Win-RHIZO system (Regent Instruments, Inc., Quebec,
Canada) on a LA 1600 scanner. Roots were spread into a
single layer on a transparent tray with a small quantity of
water, and then scanned and analyzed automatically by
the software [15].
2.4. Soluble Sugar Determination
0.2 g fresh leaves (0.5 g for roots) were extracted with 10
ml deionized water for 30 min at 100˚C. The extraction
was repeated five times. Supernatants were filtrated and
collected to a volume of 50 ml tube. Soluble sugar con-
tents in fresh leaves and roots were determined according
to Ding et al., 2006 [16].

Low Magnesium with High Potassium Supply Changes Sugar Partitioning and Root Growth Pattern Prior 603
to Visible Magnesium Deficiency in Leaves of Rice (Oryza sativa L.)
2.5. Statistical Analyses
The results were examined by analysis of variance
(ANOVA) with the statistical software SAS (V. 9.0) for
windows (SAS Institute Inc., Cary, NC. USA). Differ-
ences between means of treatments were compared using
the Fisher’s least significant difference (LSD) at the 0.05
and 0.01 probability levels.
3. Results
3.1. Visible Symptoms of Magnesium Deficiency
Rice plants in the treatment of Mg0.01K6 did not produce
visible symptoms of Mg deficiency until at day 35 after
treatment initiation. The typical visible symptoms of Mg
deficiency in rice leaves have been previously described
[16]. Since the rice seedlings had been grown in one fifth
of full nutrient solution (containing 0.2 mM Mg) for two
weeks prior to treatment initiation, the initial accumu-
lated Mg and its internal recycling in the seedlings at-
tenuated the visible signs of Mg deficiency.
3.2. Magnesium Concentrations in Shoot and
Root
With increasing concentration of Mg in the nutrient solu-
tion, Mg content in shoots of rice plants significantly
increased at day 15, 30 and 40 after treatment (Figure
1(a)). Compared with the treatments of Mg1K1, Mg con-
tent in shoot of the Mg0.01K6 treatment remarkably de-
creased. At day 40 after treatment, the Mg concentrations
in shoots of the Mg0.01K6 treatment were much lower
(0.63 mg·g–1 DW) and clearly below the critical defi-
ciency level of 1.1 mg·Mg·g–1 DW [16]. Figure 1(a) also
shows that high K supply (6 mM K) significantly re-
strained Mg uptake at different Mg supply levels from
0.01 to 1 mM Mg, demonstrating a strong antagonistic
effect between Mg and K. The Mg content in roots
showed the same trend as for shoots (Figure 1(b)). The
ANOVA results suggested that both K and Mg concen-
trations and their interaction had a significant effect on
the Mg contents in both shoots and roots of rice plants.
3.3. Magnesium Translocation
Similarly to the Mg contents in shoots and roots of rice
plants, Mg uptake in shoots and roots significantly in-
creased with increasing concentration of Mg in the nutrient
solution after treatment initiation (result not shown).
The translocation of Mg was quantified by dividing
the amount of the Mg accumulated in the shoots by the
total amount of Mg taken up in the shoots and roots [17].
The result showed that the rate of Mg translocation from
the root to the shoot of Mg0.01K6 treatment maintained a
higher level as compared with that of the Mg1K1 treat-
Figure 1. Effects of the interaction between Mg and K on
the Mg contents in shoot (a) and root (b) and the rate of Mg
translocation from the root to the shoot (c) of rice plants
after treatment initiation. The nutrient solution contained
0.01 and 1.0 mM Mg concentration, with K at 1.0 and 6.0
mM. The vertical bars are the standard error of means of
three replicates. Bars with the same small letters at the
same harvest mean not significantly difference between
treatments by the least significant difference (LSD) at the
0.05 probability level. Mg, magnesium; K, potassium; DW,
dry weight.
ment at day 15, 30 and 40 after treatment initiation. This
result indicated that increased Mg translocation from the
root to the shoot may be an adaptive response of rice
plants to the Mg stress.
3.4. Soluble Sugar Concentration in Plant
Tissues
The soluble sugar contents in leaves (Figure 2(a)), stems
(Figure 2(b)) and roots (Figure 2(c)) of rice plants were
significantly affected by external Mg concentration and
its interaction with K at day 15 after treatment initiation.

Low Magnesium with High Potassium Supply Changes Sugar Partitioning and Root Growth Pattern Prior
604
to Visible Magnesium Deficiency in Leaves of Rice (Oryza sativa L.)
Figure 2. Effects of the interaction between Mg and K on
the soluble sugar contents in shoots (a), stems (b) and roots
(c) of rice plants after treatment initiation. The nutrient
solution contained 0.01 and 1.0 mM Mg concentration, with
K at 1.0 and 6.0 mM. The vertical bars are the standard
error of means of three replicates. Bars with the same small
letters at the same harvest mean not significantly difference
between treatments by the least significant difference (LSD)
at the 0.05 probability level. Mg, magnesium; K, potassium;
FW, fresh we ight.
When Mg concentration was 1.81 mg·g–1 DW in shoots
and 0.36 mg·g–1 DW in roots, the soluble sugar content in
leaves was significantly decreased by 35.8% at Mg0.01K6
treatment, as compared with the treatment of Mg1K1
(Figure 2(a)) at day 15 after treatment. In contrast to the
leaves, the soluble sugar contents in stems and roots were
significantly increased by 10.2% (Figure 2(b)) and
29.2% (Figure 2(c)), respectively, as compared with the
treatment of Mg1K1. This result suggested that low Mg
supply with high K level alters soluble sugar partitioning
in different organs of rice plants, particularly increasing
the proportion of soluble sugars in the roots. At day 40
after treatment, Mg concentration in shoots was below
the critical deficiency level. Compared with the treatment
of Mg1K1, the soluble sugar content at Mg0.01K6 treat-
ment was significantly increased by 20.8% in leaves
(Figure 2(a)), but decreased by 37.1% and 39.2% in
stems (Figure 2(b)) and roots (Figure 2(c) ), respectively.
This result indicated that under Mg deficiency, soluble
sugars may be accumulated in leaves of rice.
3.5. Plant Growth and Root to Shoot Dry Weight
Ratio
At day 15 after treatment, dry matter yield of both shoots
(Figure 3(a)) and roots (Figure 3(b)) in the low-Mg
treatment was not significantly different compared to that
of the Mg1K1 treatment. However, the root to shoot ratio
was significantly higher than that of the Mg1K1 treatment
(Figure 3(c)). At day 30 after treatment, the shoot DW of
the Mg0.01K6 treatment was reduced by 12.9% (Figure
3(a)), whereas the root DW increased by 12.1% (Figure
3(b)) as compared with that of the Mg1K1 treatment. The
greater decrease in the dry matter of shoots and the
marked increase in roots resulted in the increased root to
shoot DW ratio (Figure 3(c)) in rice plants. At day 40
after treatment, compared with the Mg1K1 treatment, the
DW of both shoots and roots of the Mg0.01K6 treatment
was markedly reduced by 14.7% (Figure 3(a)) and
12.5% (Figure 3(b)), respectively, because of Mg defi-
ciency. The root to shoot ratio did not differ significantly
between the Mg0.01K1 and Mg1K1 treatments (Figure
3(c)). These results revealed that the increase in root to
shoot ratio occurred prior to visible Mg deficiency
symptoms in leaves of rice plants.
3.6. Root Morphology
In order to study the effects of the interaction between
Mg and K on root morphology of rice plants, we use a
Win-Rhizo LA-1600 Scanner to scan the roots of all
treatments of the experiment prior to Mg deficiency
symptoms in rice leaves. The results showed that the
total root length (Figure 4(a)), total root surface area
(Figure 4(b)), root volume (Figure 4(c)), average root di-
ameter (Figure 4(d)), total length of 0 - 0.5 mm diameter
roots (Figure 4(e)), and total length of 0.5 - 1.0 mm diame-
ter roots (Figure 4(f)) significantly increased by 11.8%,
16.4%, 25.3%, 8.1%, 16.6% and 12.5% respectively for the
Mg0.01K6 treatment at day 30 after treatment initiation, as
compared with the Mg1K1 treatment. Under Mg deficiency
at day 40 after treatment, the total root surface area
(Figure 4(b)), root volume (Figure 4(c)), average root
diameter (Figure 4(d)) were reduced by 10.9%, 21.1%

Low Magnesium with High Potassium Supply Changes Sugar Partitioning and Root Growth Pattern Prior 605
to Visible Magnesium Deficiency in Leaves of Rice (Oryza sativa L.)
Figure 3. Effects of the interaction between Mg and K on
dry matter yield of shoot (a) and root (b), and root to shoot
DW ratio (c) of rice plants after treatment initiation. The
nutrient solution contained 0.01 - 1.0 mM Mg concentra-
tion, with K at 1.0 - 6.0 mM. The vertical bars are the stan-
dard error of means of three replicates. Bars with the same
small letters at the same harvest mean not significantly dif-
ference between treatments by the least significant differ-
ence (LSD) at the 0.05 probability level. Mg, magnesium; K,
potassium; DW, dry weight.
and 11.4% respectively, except the total length of 0 - 0.5
mm diameter roots (Figure 4(e)), and total length of 0.5 -
1.0 mm diameter roots (Figure 4(f)) were increased by
13.9% and 5.0%, respectively.
3.7. Correlation Analysis
Regression analysis was performed to examine relation-
ships between the soluble sugar contents in roots, root to
shoot DW ratio and root morphological parameters of rice
plants. Table 1 shows that the soluble sugar contents in
leaves at day 15 after treatment initiation had a highly posi-
tive correlation with the total root length, total root surface
area, root volume, number of root forks, total length of 0 -
0.5 mm and 0.5 - 1.0 mm diameter roots and the root to
shoot ratio of rice plants at day 30 after treatment initia-
tion. Moreover, these root morphological parameters had
a highly positive correlation with the root to shoot ratio
at day 30 after treatment initiation. These results indicate
that the root to shoot ratio is closely related to the soluble
sugar contents in roots and root morphological parame-
ters of rice plants.
4. Discussion
In almost all higher plants, the principle end products of
leaf photosynthates are sucrose and starch. However,
partitioning of sucrose and starch and their effect on dry
matter distribution is influenced by several environ-
mental factors, such as low temperature, drought and
essential mineral nutrients [18,19]. Mineral nutritional
status of plants has a considerable impact on partitioning
of carbohydrates and dry matter between shoots and
roots [1,7,20,21]. It has long been known that deficien-
cies of essential macronutrients (N, P, K and Mg) result
in an accumulation of carbohydrates in leaves and roots,
and modify the root to shoot biomass ratio [6]. Mg defi-
ciency leads to the accumulation of sugars and starch in
young source leaves [8,16,22-25], but they rarely in-
crease their root growth because of impaired export of
carbohydrates from source to sink sites [6]. In the present
study, Mg nutritional status had a stronger effect on both
root and shoot growth and dry matter distribution of rice
plants. At day 30 after treatment initiation, shoot growth
for the Mg0.01K6 treatment was severely affected by low
Mg stress because the Mg concentration in shoots was
1.27 mg·g–1 DW (Figure 1(a)), which was near the criti-
cal deficiency level of 1.1 mg Mg·g–1 DW [16]. However,
the root growth significantly increased (Figure 3(b))
indicating that a considerable proportion of dry matter
was partitioned to the roots, leading to an increase in root
to shoot DW ratio before Mg deficiency symptoms were
visible in leaves of rice plants (Figure 3(c)). This finding
was consistent with that of Hermans et al. [6] who ob-
tained an increase in the root to shoot ratio in Arabidoop-
sis thaliana plants. We suggest that the increase in root to
shoot ratio may be closely associated with the concentra-
tions and distribution of soluble sugars in different tis-
sues of plants because there is a close relationship be-
tween shoot to root DW ratios and relative distribution of
total carbohydrates in shoots and roots [23]. The increase
of root to shoot ratio may be an important adaptive
mechanism for rice plants to low-Mg stress before visible
Mg deficiency signs in the leaves. Previous studies sug-
gest that under Mg deficiencies root growth markedly
ecreases, leading to an increase in shoot to root DW d

Low Magnesium with High Potassium Supply Changes Sugar Partitioning and Root Growth Pattern Prior
to Visible Magnesium Deficiency in Leaves of Rice (Oryza sativa L.)
606
Figure 4. Effects of the interaction between Mg and K on the root morphological parameters of rice plants after treatment
initiation. Total root length (a); Total root surface area (b); Root volume (c); Average root diameter (d); Total length of 0 -
0.5 mm diameter roots (e); Total length of 0.5 - 1.0 mm diameter roots (f). The nutrient solution contained 0.01 - 1.0 mM Mg
concentration, with K at 1.0 - 6.0 mM. The vertical bars are the standard error of means of three replicates. Bars with the
same small letters at the same harvest mean not significantly different between treatments by the least significant difference
(LSD) at the 0.05 probability level. Mg, magnesium; K, potassium.
ratios in plants [8-11].
Sugars perform important regulatory functions in
plants including photosynthesis [26] and carbohydrate
partitioning [27,28]. Soluble sugar states have been
showed to affect various aspects of physiology and de-
velopment in higher plants by up- or down-regulating the
expression of the relevant genes [26]. In this study, our
data showed that the concentration of soluble sugar for
the Mg0.01K6 treatment at day 15 after treatment was re-
duced in leaves (Figure 2(a)), but increased in roots
(Figure 2(c)) as compared with the Mg1K1 treatment,
indicating the increased translocation of sugars to the
roots, which might contribute to the increase in root to
shoot ratio in rice plants at day 30 after treatment since
the growth and development of the root system needs
more sugar supply. Furthermore, correlation analysis
also revealed that there was a significantly positive linear
correlation between the soluble sugar contents in roots of
rice plants at day 15 and the root to shoot DW ratio at day
0 after treatment (Table 1). Under Mg deficiency, the 3

Low Magnesium with High Potassium Supply Changes Sugar Partitioning and Root Growth Pattern Prior 607
to Visible Magnesium Deficiency in Leaves of Rice (Oryza sativa L.)
Table 1. Correlation coefficients between sugar content in root at day 15 and root to shoot ratio and root parameters of rice
plants at day 30 after treatment initiation. Rice plants were grown in the nutrient solution contained 0.01 and 1.0 mM Mg
concentration, with K at 1.0 and 6.0 mM. The root parameters of rice were obtained by using a scanner at day 30 after
treatment initiation.
Items Total root
length
Total surface
area of root Root volumeNumber of root forks
Total length of 0 - 0.5 mm
diameter roots
Total length of 0.5 - 1
mm diameter roots
Root to shoot
ratio
Sugar content in root
at day 15 0.866** 0.630** 0.601** 0.818** 0.754** 0.759** 0.661**
Root to shoot ratio
at day 30 0.664** 0.694** 0.800** 0.812** 0.627** 0.642** ―
Shown are R values (n = 12), significant differences are indicated by the asterisks (**Significant at the 0.01 probability level).
soluble sugar contents in leaves were significantly increased
at day 40 after treatment (Figure 2(a)) but markedly re-
duced in roots (Figure 2(c)) because of impaired export of
carbohydrates from leaves to roots. This observation is in
agreement with that of Hermans et al. [25]. As the mecha-
nism of sugar regulation involved in carbohydrate metabo-
lism, long-distance transport and partitioning remains un-
known, further intensive studies in physiological and mo-
lecular level are required.
Root morphology and architecture are the primary
traits that influence plant resource acquisition [29]. Root
growth requires nutrients that are absorbed from the ex-
ternal culture medium and photosynthates that are trans-
ported from the shoot. It is evident that sugar supply is
one of the most important factors limiting growth of the
root system [30]. Hermans et al. [6] suggest that root
morphology alterations are closely related to the regula-
tion of sugars and hormones in plants. The results in
Figure 4 indicate that the enhanced total root length
(Figure 4(a)), total surface area (Figure 4(b)), root
volume (Figure 4(c)), average root diameter (Figure
4(d)) and total length of 0 - 0.5 mm (Figure 4(e)) and 0.5
- 1.0 mm diameter roots (Figure 4(f)) may be related to
enhanced concentration of soluble sugars in roots of rice
at day 15 after treatment initiation. The correlation
analysis indicated that the root to shoot ratio is closely
related to the soluble sugar contents in roots and root
morphological parameters of rice plants (Table 1).
In conclusion, low Mg with high K supply alters solu-
ble sugar partitioning and root morphological parameters,
restrains shoot growth but enhances root growth, and
thereby increases root/shoot DW ratio before visible Mg
deficiency symptoms appear in rice leaves. These re-
sponses may represent a primary adaptive mechanism for
rice plants to Mg stress during the early growth stage.
5. Acknowledgements
We thank Professor Richard M. Cruse and Heidi Asb-
jornsen of Iowa State University for their critically read-
ing and correcting the English language of the manu-
script. This research was financially supported in part by
the Dead Sea Works Ltd., Israel.
REFERENCES
[1] H. Marschner, “Mineral Nutrition of Higher Plants,” 2nd
Edition, Academic Press, London, 1995.
[2] O. Shaul, “Magnesium Transport and Function in Plants:
the Tip of the Iceberg,” Biometals, Vol. 15, No. 3, Sep-
tember 2002, pp. 309-323.
doi:10.1023/A:1016091118585
[3] S. Shabala and Y. Hariadi, “Effects of Magnesium Avail-
ability on the Activity of Plasma Membrane Ion Trans-
porters and Light-Induced Responses from Broad Bean
Leaf Mesophyll,” Planta, Vol. 221, No. 1, April 2005, pp.
56-65. doi:10.1007/s00425-004-1425-0
[4] C. Hermans, F. Bourgis, M. Faucher, R. J. Strasser, S.
Delrot and N. Verbruggen, “Magnesium Deficiency in
Sugar Beets Alters Sugar Partitioning and Phloem Load-
ing in Young Mature Leaves,” Planta, Vol. 220, No. 4,
October 2005, pp. 541-549.
doi:10.1007/s00425-004-1376-5
[5] K. Mengel and E. A. Kirkby, “Principles of Plant Nutri-
tion,” 4th Edition, International Potash Institute, Switzer-
land, 1987.
[6] C. Hermans, J. P. Hammond, P. J. White and N. Verbr-
uggen, “How Do Plants Respond to Nutrient Shortage by
Biomass Allocation?” Trends in Plant Science, Vol. 11,
No. 12, December 2006, pp. 610-617.
doi:10.1016/j.tplants.2006.10.007
[7] H. Marschner, E. A. Kirkby and I. Cakmak, “Effect of
Mineral Nutritional Status on Shoot-Root Partitioning of
Photoassimilates and Cycling of Mineral Nutrients,”
Journal of Experimental Botany, Vol. 47, No. Special Is-
sue, August 1996, pp. 1255-1263.
doi:10.1093/jxb/47.Special-Issue.1255
[8] I. Cakmak, C. Hengeler and H. Marschner, “Partitioning
of Shoot and Root Dry Matter and Carbohydrates in Bean
Plants Suffering from Phosphorus, Potassium and Magne-
Sium Deficiency,” Journal of Experimental Botany, Vol.
45, No. 9, September 1994, pp. 1245-1250.

Low Magnesium with High Potassium Supply Changes Sugar Partitioning and Root Growth Pattern Prior
608
to Visible Magnesium Deficiency in Leaves of Rice (Oryza sativa L.)
[9] T. Ericsson, “Growth and Shoot: Root Ratio of Seedlings
in Relation to Nutrient Availability,” Plant and Soil, Vol.
168-169, No. 1, 1995, pp. 205-214.
[10] C. Hermans, G. N. Johnson, R. J. Strasser and N. Ver-
bruggen, “Physiological Characterization of Magnesium
Deficiency in Sugar Beet: Acclimation to Low Magne-
sium Differentially Affects PhotosystemsⅠand Ⅱ,”
Planta, Vol. 220, No. 2, 2004, pp. 344-355.
doi:10.1007/s00425-004-1340-4
[11] R. K. Tewari, P. Kumar and P. N. Sharma, “Magnesium
Deficiency Induced Oxidative Stress and Antioxidant Re-
sponses in Mulberry Plants,” Scientia Horticulturae, Vol.
108, No. 1, March 2006, pp. 7-14.
doi:10.1016/j.scienta.2005.12.006
[12] N. K. Fageria, “Dry Matter Yield and Nutrient Uptake by
Lowland Rice at Different Growth Stages,” Journal of
Plant Nutrition, Vol. 27, No. 6, 2004, pp. 947-958.
[13] S. Yoshida, D. A. Forno, G. H. Cock and K. A. Gomez,
“Laboratory Manual for Physiological Studies of Rice,”
2nd Edition, International Rice Research Institute, Los
Banos, 1972.
[14] J. R. Lowther, “Use of a Single Sulphuric-Hydrogen Per-
oxide Digest for the Analysis of Pinus radiate Needles,”
Communications in Soil Science and Plant Analysis, Vol.
11, No. 2, 1980, pp. 175-188.
[15] L. Villarreal-Ruiz, I. C. Anderson and I. J. Alexander,
“Interaction between an Isolate from the Hymenoscyph-
us Ericae Aggregate and Roots of Pinus and Vaccinium,”
New Phytologist, Vol. 164, No. 1, October 2004, pp. 183-
192. doi:10.1111/j.1469-8137.2004.01167.x
[16] Y. Ding, W. Luo and G. Xu, “Characterization of Magne-
sium Nutrition and Interaction of Magnesium and Potas-
sium in Rice,” Annals of Applied Biology, Vol. 149, No. 2,
October 2006, pp. 111-123.
doi:10.1111/j.1744-7348.2006.00080.x
[17] T. Ohno and D. L. Grunes, “Potassium-Magnesium In-
teraction Affecting Nutrient Uptake by Wheat Forage,”
Soil Science Society of America Journal, Vol. 49, No. 3,
1985, pp. 685-690.
[18] S. C. Huber, “Biochemical Mechanism for Regulation of
Sucrose Accumulation in Leaves during Photosynthesis,”
Plant physiology, Vol. 91, No. 2, October 1989, pp. 656-
662.
[19] I. A. Wardlaw, “The Control of Carbon Partitioning in
Plants,” New Phytologist, Vol. 116, No. 3, November
1990, pp. 341-381.
[20] U. Druege, S. Zerche, R. Kadner and M. Ernst, “Relation
between Nitrogen Status, Carbohydrate Distribution and
Subsequent Rooting of Chrysanthemum Cuttings as
Affected by Pre-Harvest Nitrogen Supply and Cold-
storage,” Annals of Botany, Vol. 85, No. 5, May 2000, pp.
687-701. doi:10.1006/anbo.2000.1132
[21] J. López-Bucio, A. Cruz-Ramirez and L. Herrera-Estrella,
“The Role of Nutrient Availability in Regulating Root
Architecture,” Current Opinion in Plant Biology, Vol. 6,
No. 3, Jun 2003, pp. 280-287.
doi:10.1016/S1369-5266(03)00035-9
[22] I. Cakmak and H. Marschner, “Magnesium Deficiency
and High Light Intensity Enhance Activities of
Superoxide Dismutase, Ascorbate Peroxidase, and Gluta-
thione Reductase in Bean Leaves,” Plant Physiology, Vol.
98, No. 4, April 1992, pp. 1222-1227.
[23] I. Cakmak, C. Hengeler and H. Marschner, “Changes in
Phloem Export of Sucrose in Leaves in Response to Phos-
phorus, Potassium and Magnesium Deficiency in Bean
Plants,” Journal of Experimental Botany, Vol. 45, No. 9,
September 1994, pp. 1251-1257.
[24] E. S. Fischer, G. Lohaus, D. Heineke and H. W. Heldt,
“Magnesium Deficiency Results in Accumulation of
Carbohydrates and Amino Acids in Source and Sink
Leaves of Spinach,” Physiologia Plantarum, Vol. 102,
No.1, January 1998, pp. 16-20.
[25] C. Hermans and N. Verbruggen, “Physiological Charac-
terization of Mg Deficiency in Arabidopsis Thaliana,”
Journal of Experimental Botany, Vol. 56, No. 418, Au-
gust 2005, pp. 2153-2161. doi:10.1093/jxb/eri215
[26] F. Rolland, B. Moore and J. Sheen, “Sugar Sensing and
Signaling in Plants,” The Plant Cell, Vol. 14, No. Supply,
May 2002, pp. 185-205. doi:10.1105/tpc.010455
[27] T. J. Chiou and D. R. Bush, “Sucrose Is a Signal
Molecule in Assimilate Partitioning,” Proceedings of the
National Academy of Sciences of the United States of
America, Vol. 95, No. 8, April 1998, pp. 4784-4788.
[28] F. Rook and M. W. Bevan, “Genetic Approaches to
Understanding Sugar-Response Pathways,” Journal of
Experimental Botany, Vol. 54, No. 382, January 2003, pp.
495-501. doi:10.1093/jxb/erg054
[29] H. Wang, Y. Inukai and A. Yamauchi, “Root Deveiop-
ment and Nutrient Uptake,” Critical Reviews in Plant
Sciences, Vol. 25, No. 3, May 2006, pp. 279-301.
doi:10.1080/07352680600709917
[30] W. R. John, L. P. Linda and R. S. Charles, “Partitioning
of Sugar between Growth and Nitrate Reduction in
Cotton Roots,” Plant Physiology, Vol. 62, No. 4, October
1978, pp. 550-553.