Vol.4, No.5B, 112-115 (2013) Agricultural Sciences
doi:10.4236/as.2013.45B021
Effect of heat stress on the MDA, proline and soluble
sugar content in leaf lettuce seedlings
Yingyan Han, Shuangxi Fan*, Qiao Zhang, Yanan Wang
Department of Plant Science and Technology, Beijing Agricultural College, Beijing, China; *Corresponding Author: fsx20@163.com
Received 2013
ABSTRACT
High temperature stress on different varieties of
lettuce seedlings in MDA, proline and soluble
sugar content were studied. The results w ere as
follows : With the stress temperature, varieties
of leaf lettuce seedlings in the MDA, proline and
soluble sugar content gradually increased; Dif-
ferent varieties had the most significant differ-
ence in 38/33 (d/n). The increase of heat-re-
sistant varieties on proline and soluble sugar
content was quick and high, while it s increas e in
MDA content was slow and small.
Keywords: Leaf Lettuce; High Temperature; MDA;
Praline; Soluble Sugar
1. INTRODUCTION
Leaf lettuce (Lactuca sative L.) native to the Mediter-
ranean coast liked the cold weather, and was prone to rot
species, seedling difficult, easy bolting, perishable and
other obstacles at high temperature, causing yield and
quality difficult to achieve the desired goal. Therefore,
fostering resistant varieties of leaf lettuce had to be re-
solved, and the problem of heat-resistant type of leaf
lettuce seedling formation and growth was an important
prerequisite for cultivating heat-resistant varieties. Cur-
rently more heat tolerance of vegetable was cabbage[1-3],
and the heat resistance of leaf lettuce on a rarely reported.
Study of this experiment in heat stress conditions, the
different varieties of leaf lettuce seedlings in the MDA,
proline and soluble sugar content, was designed to heat-
resistant varieties of leaf lettuce to provide a theoretical
basis.
2. TEXT
2.1. Material and Methods
2.1.1. Plant materials
There were significant differences in heat resistance of
four cultivars: S24, S39 for the heat-resistant varieties,
and J20, J2 is for the non-heat-resistant varieties.
2.1.2. High Temperature Treatments
When the seedlings to 4 or 5 leaves, when all varieties
of the same robust growth state selected plants, placed in
artificial climate boxes at 25/20 (d/n) (CK), 30/25
(d/n), 38/33 (d/n), 42/37 (d/n) for high temperature
treatment. Illumin ation period of 12 h/12 h (d/n), and air
humidity of (70 ± 5)%. To avoid the impact of drought,
the water treatment quantitative to maintain consistent
soil moisture. 10 seedlings per treatment were randomly
arranged. 3d after treatment were consistent with the
growth of leaves taken, immediately placed in liquid
nitrogen fixed -80 refrigerator.
2.1.3. The Content of MDA
The content of MDA was measured by thiobarbituric
acid colorimetry[4,5].
2.1.4. The Content of Proline
The content of proline was measured by sulfosalicylic
acid colorimetry[6].
2.1.5. The Content of Soluble Sugar
The content of soluble sugar was measured by an-
throne colorimetry[7] .
2.2. Results and Discussion
2.2.1. Effects of Heat Stress on MDA in Leaf
Lettuce Seedlings
Under stress conditions, MDA, as products of lipid
peroxidation, the level of its content was often used to
explain the extent of peroxidation. Figure 1 showed that
with increasing temperature, the content of MDA in-
creased. 30/25 (d/n), the content of MDA of S24 and
J20 increased slightly, but compared with the control, the
increase was not significant; The content of MDA of S39
and J2 was increased by 60.03% and 43.30%, to reach a
significant level. From this description, the content of
MDA of the non-heat-resistant varieties than the
heat-resistant varieties increased rapidly. 38/33 (d/n),
The content of MDA of S24 and S39 was increased by
50.70% and 97.49%, the MDA content of J20 and J2
increased 55.04% and 77.49% . Compared with control,
Copyright © 2013 SciRes. Openly accessible at http://www.scirp.org/journal/as/
Y. Y. Han et al. / Agricultural Sciences 4 (2013) 112-115 113
species difference between the increase in MDA content
was significant, the increase of the content of MDA of
the heat-resistant varieties than the non-heat-resistant
varieties in small. The increase of the content of MDA
was related with varieties of heat resistance. 42/37
(d/n), all varieties were higher the content of MDA, but
compared with the control, varieties was no significant
difference between the content of MDA of increase.
2.2.2. Effects of Heat Stress on Proline in Leaf
Lettuce Seedlings
Proline as a kind of osmotic adjustment, under stress
the increase of proline content was benefit to stress in
plant resistance to a certain extent, enhancing the
adaptability of organisms to environmental stress. Figure
2 shows that with the temperature, the proline content of
the four kinds of leaf lettuce seedlings was rising. 30/25
(d/n), the proline con tent of S39 and J2 increased slightly,
but compared with the control, the increase was not sig-
nificant; the proline content of S24 and J20 was in-
creased by 27.01% and 22.40%, reached a significant
level. It showed the proline content of non-heat-resistant
varieties than heat-resistant varieties increased rapidly.
38/33 (d/n) , compared with the control, the increase
of proline of S24 w as 94.62%, S39 was 20.54%. J2 0 was
52.81%, and J2 was 13.82%, the most significant differ-
ence among varieties .42/37 (d/n), the proline content
of all varieties began to decrease, the increase of S24 and
J20 was significantly higher than the control, while the
S39 and J2 of the increase was not significant compared
with the control. These resu lts suggest that the content of
proline was related with varieties of heat resistance, the
heat-resistant varieties of proline content and growth
were higher.
2.2.3. Effects of Heat Stress on the Content of
Soluble Sugar in Leaf Lettuce Seedlings
Soluble sugar h elped reduce th e cell osmotic potential,
reduced water losses, and its role was important in re-
search of physiology. As can be seen from Figure 3, with
increasing temperature, leaf lettuce seedling soluble
sugar content increased significantly. 30/25 (d/n),
soluble sugar content of S24 and S39 was increased 1.68
times and 1.28 times, J20, and J2 was increased 1.43
times and 1.67 times. 38/33 (d/n), the peak of soluble
sugar content was reached. Compared with the control,
soluble sugar content of S24 and J20 respectively was
increased 2.48 times and 2.83 times, S39 and J2 was in-
creased 2.43 and 2.13 times respectively. Temperatures
continue to rise, the soluble sugar content of leaf lettuce
seedlings decreased slightly. These results indicated that
under heat stress, the soluble sugar content of leaf lettuce
increased, its content of heat-resistant varieties of seed-
lings higher than th e non-heat-resistant varieties.
0.00
100.00
200.00
300.00
400.00
500.00
600.00
25/20℃ 30/25℃38/33℃ 42/37℃
temperature
MDA
nmol/g
S24
S39
J20
J2
Figure 1. Effects of heat stress on MDA in leaf lettuce seedlings.
0.00
2.00
4.00
6.00
8.00
10.00
12.00
14.00
16.00
25/20℃ 30/25℃ 38/33℃ 42/37℃
temperature
PRO
ug/g
S24
S39
J20
J2
Figure 2. Effects of heat stress on the content of proline in leaf lettuce seedlings.
Copyright © 2013 SciRes. Openly accessible at http://www.scirp.org/journal/as/
Y. Y. Han et al. / Agricultural Sciences 4 (2013) 112-115
114
0.00
0.20
0.40
0.60
0.80
1.00
25/20℃ 30/25℃ 38/33℃ 42/37℃
temperature
soluble sugar
%
S24
S39
J20
J2
Figure. 3. Effects of heat stress on the content of soluble sugar in leaf lettuce seedlings.
Many studies showed that the cell membrane more
sensitive to high temperature, was the core issues of h eat
damage and heat resistance of plant. Thylakoid mem-
brane and the plasma membrane than the mitochondria
were more susceptible to heat damage [8]. Heat stress
often leaded to oxidative stress, reactive oxygen species
(ROS) accumulation, Eventually leading to membrane
peroxidation, protein structure damage and DNA in-
jury[9-11]. MDA was a lipid peroxidation of product, its
content reflected the lev el of lipid levels by the injury. In
this study, with the temperature, the MDA content of leaf
lettuce of all varieties had increased, and high tempera-
ture stress on the non-heat-resistant varieties of mem-
brane stability was greater damage than the heat-resistant
varieties. This is Li Min[12] consistent with the findings
of the spinach.
However, the response of plants to heat stress was not
entirely passive, the body would occur through various
mechanisms and appropriate adaptive response to resis-
tance or to avoid harm to maintain basic metabolic pro c-
esses. Proline and soluble sugar to osmotic adjustment,
the increase of its concentration could increase the con-
centration of cell protoplasm, to maintain normal mem-
brane function at high temperatures to be conducive to
plant resistance of environmental stress, which could be
enhanced to some exten t the adaptability of organisms to
environmental stress. In this study, with the temperature,
leaf lettuce seedlings proline and soluble sugar content
increased, and the rate of increase in differences between
species, the heat-resistant varieties of increase was sig-
nificantly higher than the heat of the non-heat-resistant
varieties. The results were as the same as the proline
changes of tomato under high temperature stress [13].
But the soluble sugar content of eggplant was decreased
under high temperature [14], and Dioscorea zingibercnsis
leaves in the soluble sugar content showed a trend of
low-high-low level [15]. Results of this paper were not
agree with them and further studies are needs.
3. CONCLUSIONS
MDA con tent in radicles increased significantly as the
processing temperature rising, and the most obvious was
that in the range of 35 - 40. The strong heat-resistant
varieties were lower of MDA than the weak
heat-resistant varieties. Theses show that membrane sys-
tem was hurt under the high-temperature, and the weak
heat-resistant varieties of destruction were more serious.
Activity of cell protective enzymes showed a downward
trend after the first rise, 30, all varieties of SOD and
POD activity reached a maximum; 35, the various
varieties of SOD and POD activity was significantly de-
creased, and there was the most significant difference
between varieties. The strong heat-resistant varieties of
these two protective enzyme activities were higher than
the weak heat-resistant varieties. Researches showed that
to maintain a high membrane protective enzyme activity
can reduce the heat hazards.
4. ACKNOWLEDGEMENTS
This work was supported by the earmarked fund for Beijing Leafy-
Vegetables Innovation Team of Modern Agro-industry Technology
Research System (Number blvt-02), the “Beijing Nova Program”
(Number 2010B020) and the “Beijing Natural Science Foundation”
(Number 6112005).
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