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that without NaCl treatment and 7
-
fold higher than the
NS at the 100 mmol/L NaCl concentration (Figure 2).
When salt stress was in 150 mmol/L NaCl concentration
levels, the enzyme activity decreased in TS and NS,
because cell plasmid membrane was destructed
seriously and antioxidant enzymes were inactivates.
By contrast to TS, the enzyme activities of NS
decrease sharply, even increased few or decreased
below the 100 mmol/L NaCl concentration level,
SOD activity decreased under the 50 mmol/L NaCl
concentration level. These showed that transgenic
sweetpotato might efficiently tolerate the salt stress,
because excessive expression of SOD-APX gene with
the stress-inducible promoter.
Figure 2 SOD, APX, CAT and POD activities in sweet potato leaves under NaCl stress
Note: Values are the means of at least three different experiments ± SD; Differences between NS and TS values in the same treatment
were significant at: *: P <0.05, **: P<0.01, according to Duncan's Multiple Range Test
1.3 MDA (Malondialdehyde) content
The MDA is one of the final products of the cell
membrane damage because of free radicals attack.
The MDA content positively correlated with NaCl
concentration. There was no remarkable difference
without NaCl stress between TS and NS, however,
there were remarkable differences under NaCl stress
between TS and NS (P<0.01 and P<0.01; Figure 3).
The MDA content of TS was lowest under the 100
mmol/L NaCl concentration level, resulting from high
enzyme activities which cleaned extra MDA, thereby
reduced the damage of the cell membrane. When salt
stress was in 150 mmol/L NaCl concentration levels,
the MDA content increased in TS and NS, because cell
plasmid membrane was destructed and the enzymes
activities declined.
Figure 3 MDA content in sweet potato leaves under NaCl stress
Note: Values are the means of at least three different
experiments ± SD; Differences between NS and TS values in
the same treatment were significant at: *: P<0.05, **: P<0.01,
according to Duncan's Multiple Range Test
1.4 Chlorophyll content
The chlorophyll content of the leaf reduced due to
NaCl stress (Rao and Rao, 1981). There was no