The Accumulation and Physio-Biochemical Characteristics of Three
Cassava Cultivars under As Stress
Pan Pan
1,2
, Beibei Liu
1,2*
, Lin Wu
1,2
, Chunyuan Wu
1,2
and Qinfen Li
1,2
1
Environment and Plant Protection Institute, Chinese Academy of Tropical Agricultural Sciences, Haikou, Hainan, China
2
Agricultural Environmental Science Observation and Experiment Station, Ministry of Agriculture, Danzhou, Hainan, China
Keywords: Cassava, Arsenic, Accumulation characteristics, Physio-biochemical characteristics
Abstract: Cassava is one of the most important crops in tropical regions. Due to multiple mining activities, arsenic (As)
pollution becomes a serious problem in planting lands. In this study, a hydroponic experiment was carried out
to ascertain the influence of As on three cassava cultivars (sc12, 8229 and sc6068). The three cassava cultivars
showed different accumulation and response characteristics to As. The 8229 was apt to accumulate As in the
root. Low As concentration promoted the growth of 8229 but inhibited that of sc12 and sc6068. This indicated
that 8229 is more tolerant to As than the other two cassava cultivars. The malondialdehyde (MDA) of the
three cassava cultivars, both in roots and leaves, were elevated with increasing As concentration. This study
could be a reference for cassava planting in safety.
1 INTRODUCTION
Cassava (Manihot esculenta crantz) is a woody
perennial root crop belonging to the Euphorbiaceae
family. It is an adaptable crop that can survive in
infertile soil or marginal environments (Nassar and
Ortiz, 2010). It has being cultivated abundantly in the
tropics and subtropics (Hannah et al., 2017). Cassava
tuber is organically rich in starch and carbohydrates,
and is a staple food crop in some areas of Africa,
South America and Southeast Asia (Okudoh et al.,
2014). In China, cassava is one of the most important
crops in tropical regions like Hainan, Guangdong,
Guangxi and Yunnan provinces (Yao and Zhang,
2017). However, there are a number of mine fields
located in these regions, which caused a serious
problem of toxic element pollution. Arsenic (As) is
one of the toxic trace elements, the report on China’s
soil pollution stated that 2.7% of soil is polluted by
As (MEP and MLR of P. R. China, 2014). Cassava is
apt to accumulate toxic metals. When cultivated in
Au mining area in Ghana, it accumulated zinc and
lead which far exceeded the recommended levels for
daily consumption (Zango et al., 2013). As primary
soil pollutant in China, As has threatened the safety
of agricultural products. To understand the
accumulating characteristics of As in crops is very
important for food safety.
Cultivars have a great impact on accumulation
ability of toxic trace metals, and the breeding of
cultivars is a widely applied technique for selecting
low accumulating varieties of crops such as wheat
and maize for ensuring food safety (Fu et al., 2011;
Xing et al., 2016). But there is little research
reporting about the accumulation ability of toxic
elements by different cassava cultivars so far. In
order to understand the accumulation ability for As
by different cassava cultivars and give a reference for
cassava safe planting, a hydroponic experiment was
conducted to ascertain the influence of As
concentration on the growth of different cassava
cultivars. Specifically, the aims of this study
including (1) the accumulation characteristics for As
of three cassava cultivars and (2) the influence of As
on the growth and physiological metabolism of the
three cassava cultivars.
2 MATERIALS AND METHODS
2.1 Hydroponic Experiments
Stem cuttings (about 15 cm tall, 0.8 cm in diameter)
of three cassava cultivars (sc12, 8229, sc6068) were
selected for propagation and cultivation. They were
conducted in a pot with a modified Hoagland nutrient
268
Pan, P., Liu, B., Wu, L., Wu, C. and Li, Q.
The Accumulation and Physio-Biochemical Characteristics of Three Cassava Cultivars under As Stress.
DOI: 10.5220/0008188702680272
In The Second International Conference on Materials Chemistry and Environmental Protection (MEEP 2018), pages 268-272
ISBN: 978-989-758-360-5
Copyright
c
2019 by SCITEPRESS – Science and Technology Publications, Lda. All rights reserved
solution, the pH value was adjusted to 6.5 using
diluted HCl or NaOH. After growing for 2 weeks,
cuttings with new roots and leaves were transplanted
to Hoagland nutrient solution containing different
concentration of As. The sets with no As addition was
the control treatments, denoted by CK. The
concentration of As was set with a high level (0.5
mg/L) and a low (0.05 mg/L) level according to the
V-level Quality Standard of surface water (GB
3838-2002) (0.1 mg/L). Cuttings were bond by
sponge and fixed on cystosepiment, and were allowed
to grow and observed for 4 weeks. Hoagland nutrient
solution with As were renewed every 3 days to keep
the As concentration unchanged. Each treatment was
replicated 3 times. After 4 weeks, cassava were
harvested, washed with tap water, and then rinsed
thrice with deionized water. The plant height
(distance from the top of the plant to the bottom of the
root) was measured. The cassavas were segregated
into shoot (including leaves and stems) and roots.
Each part was placed in individually labelled paper
bags and oven-dried at 60℃ for 7 days. After drying,
each sample was weighted for biomass assessment.
2.2 Chemical Analysis
The plant samples were digested with 5 mL HNO
3
using microwave digestion system (Mars 6, CEM,
US). Samples of certified standard reference
materials GSV-2 from the China National Standard
Materials Centre was analysed with the experimental
samples. Arsenic concentrations were determined
using an atomic fluorescence spectrometer
(AFS-8220, Beijing Jitian Instrumental Co., Ltd.,
Beijing, China).
The ability of cassava to translocate As from roots
to shoots was measured by calculating translocation
factor (TF) using the following formula:
TF=As concentration in shoots/As concentration in
roots.
The malondialdehyde (MDA) was measured
according to Heath and Packer (Heath and Packer,
1968). In brief, 0.5g root or shoot of cassava was
centrifuged at 3000 r/min for 10 min after being
homogenized in 5 mL of 5% TCA. The collected
supernatant (2 mL) was added to 2 mL of 0.67%
TBA. The mixture was heated in water bath at 100℃
for 30 min, then cooled and re-centrifuged at 3000
r/min. The supernatant were measured at 450 nm, 532
nm and 600 nm.
2.3 Data Analysis
Variance analysis was conducted using the SPSS
20.0. Data are presented as mean values SE, and
difference of means was subjected to the least
significant difference (LSD) test at 0.05 probability
level. All graphs were carried out with Origin Pro
2016 (OriginLab, USA).
3 RESULTS AND DISCUSSION
3.1 Accumulating Characteristics of As
by Three Cassava Cultivars
The accumulated As in the shoot and root of 8229
cultivar were significantly (p<0.05) higher than the
other two cultivars under both low and high
concentration, but with lowest TFs. This indicated
that 8229 was apt to accumulate As in root. Root is
the main edible part of cassava, which means that a
high risk of food pollution when 8229 is planted in As
contaminated soils. In contrast, sc12 showed a low
accumulating ability for As but had highest TFs,
demonstrating that it was low-risk in As
accumulation. To get a deep understanding of the risk
of As contamination in cassava, the concentration of
As in cassava were compared with their limit values
according to the national standards for food safety
(GB2762-2017) in Table 1. Only the concentration of
As in roots of 8229 (0.802±0.021 mg/kg) under the
treatment with 0.5mg/L As exceeds the limit value
(0.5 mg/kg). Which again suggested 8229 has a high
risk of As accumulation.
Its high accumulation of toxic elements had been
reported by previous studies. Cassava accumulated
up to 12.59 g/kg Hg and 18.99 mg/kg Au in its fibrous
roots, thus it was considered as a suitable candidate
for Hg and Au remediation (Hannah et al., 2017).
Cassava could extract 30.58 g of Cd and 3174.69 g of
Pb per hectare a year, suggesting a tremendous
potential application in soil remediation (Shen et al.,
2013).
The Accumulation and Physio-Biochemical Characteristics of Three Cassava Cultivars under As Stress
269
Table 1: The accumulation characteristics of As by three cassava cultivars.
Concentration
Cultivars
Uptake by
Transfer factor
(TF)
Limited value in
food*
Shoot(mg/kg)
Root(mg/kg)
0.05 mg/L
sc12
0.05(3.0E-03)b
0.125(1.0E-03)b
0.42(0.03)a
0.5 mg/kg
8229
0.07(6.0E-03) a
0.300(1.5E-02)a
0.22(0.01)c
sc6068
0.05(1.0E-03)b
0.137(2.0E-03)b
0.38(0.01)b
0.5 mg/L
sc12
0.08(1.1E-03)b
0.236(1.0E-01)c
0.32(0.03)a
8229
0.10(9.0E-03)a
0.802(2.1E-02)a
0.13(0.002)c
sc6068
0.08(2.8E-03)b
0.309(3.4E-02)b
0.26(0.03)b
3.2 The Height and Weight of Cassava
under As Stress
To figure out how As influences the cassava growth,
we measured their height and weight under different
concentration of As (Figure 1). Under the stress of
0.05 mg/L As, only the weight of sc12 was
significantly (p<0.05) lower than that of its control.
While under the stress of 0.5 mg/L As, the height of
sc12 and sc6068 were significantly lower than their
controls, the weight of three cassava cultivars
significantly (p<0.05) decreased compared with their
controls. This indicated that sc12 was more sensitive
to As than 8229 and sc6068. However, 8229 was
most tolerant to As.
In this study, high concentration of As showed
inhibition to cassava growth, while low concentration
had no significant effect on growth. The inhibition of
inorganic pollutants to crops has been reported by
other studies. The weight of Sedum aizoon was
promoted by 2 mg/L Cd but inhibited by 5 mg/L Cd
(Guo et al., 2018). Low Pb concentration (1000
mg/L) had promotional effect on height and biomass
of Pogonatherum crinitum, but high Pb concentration
(2000 mg/L and 3000 mg/L) had inhibition effect on
its shoot height and leaf biomass (Han et al., 2018).
Figure 1: The height and weight of three cassava cultivars
under the stress of As. Different letters indicated a
significant difference at p<0.05 (same as in Figure 2).
3.3 Resistance Reaction of Cassava
under As Stress
Malonaldehyde (MDA) is an index of cell membrane
damage. Arsenic had a great impact on MDA in root
and leaf of the three cassava cultivars (Figure 2). The
roots MDA of 8229 and sc6068 under the stress of
0.05mg/L and 0.5 mg/L As were significantly
(p<0.05) higher than their controls. But As had
indistinctive impact on that of sc12, which might be
related to its low accumulation ability for As
(showing in Table 1). Under the stress of 0.5mg/L As,
the leaf MDA of three cassava cultivars were all
significantly (p<0.05) increased, as compared with
their controls. However, under the stress of 0.05
mg/L As, only the leaf MDA of sc6068 was
observably (p<0.05) increased than its control,
MEEP 2018 - The Second International Conference on Materials Chemistry and Environmental Protection
270
indicating sc6068 was more susceptive to As stress
than sc12 and 8229 in leaf. The increased MDA
contents followed the order of sc6068>8229>sc12, in
the root of cassava under both As levels. These
findings suggested that sc12 had the lowest MDA
increment and strong tolerant for As. However,
sc6068 had the highest increment for As, showing an
intolerant ability.
sc12 8229 sc6068
0.00
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
a
a
b
a
b
b
a
ab
MDA in leaf (μmol/g)
CK As 0.05mg/L As 0.5mg/L
b
sc12 8229 sc6068
0.00
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
c
b
a
b
a
a
a
a
a
MDA in root (μmol/g)
Figure 2: The malonaldehyde in root and leaf of three
cassava cultivars under different concentration of As.
Malonaldehyde is one of the most important
products of lipid peroxidation. Under the stress of
toxic elements, plants are known to produce more
“reactive oxygen species” (ROS), which
subsequently cause the lipid peroxidation (Shahid et
al., 2014). Malonaldehyde is often used as an
indicator of the extent of oxidative stress. The content
of MDA in each cassava cultivar increased along
with increasing of As concentration, suggesting that
cassava suffered oxidative stress by As. Similar
increment of MDA has been observed in Brassica
napus (Ali et al., 2015) and maize (Anjum et al.,
2016). The varied MDA content is related with ROS
scavenging ability. Compared between two maize
cultivars, a lower MDA was observed in Dong Dan
80 than Run Nong 35 in the stress of Cd and Cd+As,
which indicated that Dong Dan 80 exhibited more
efficient ROS scavenging system (Anjum et al.,
2016). In this study, sc12 had the lowest MDA
increment for As. It could be speculated that it has a
strong ROS scavenging ability.
4 CONCLUSIONS
Three cassava cultivars, sc12, 8229 and sc6068,
showed different accumulation and response
characteristics to As stress. The 8229 was apt to
accumulate As in roots. Low As concentration had a
promotion on the growth of 8229, showing a high
accumulation capacity for As. Sc12 had a low
accumulation capacity for As. The MDA of the three
cassava cultivars, both in roots and leaves, were
increased with increasing As concentration,
suggesting that cassava has a resistant reaction at
physio-biochemical level. These findings could be a
reference for planting cassava in safety.
ACKNOWLEDGEMENTS
This work was supported by the Central
Public-interest Scientific Institution Basal Research
Fund for Chinese Academy of Tropical Agricultural
Sciences Environment and Plant Protection Institute
(No.2016hzs1J008, No.2018hzs1J004) and the Major
Science and Technology Program of Hainan Province
(ZDKJ2017002).
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