Abstract
A study was taken to find out the soybean genotypes tolerant to salt, response to
salinity and cloning of antiporter genes to develop salt tolerant transgenic soybean.
Six experiments were carried out regarding in vitro screening of soybean genotypes
at 80 mM NaCl, molecular characterization of soybean genotypes by salt tolerant
SSR (Simple Sequence Repeat) markers, response of selected soybean genotypes for
different salinity levels under in vitro conditions, physio-biochemical response of
soybean to salt stresses, expression of AtNHX1 and ThNHX1 genes under different
salinity stresses and cloning of AtNHX1 and ThNHX1 genes in Agrobacterium. These
experiments were done at USDA-Biotechnology Laboratory, Department of
Biotechnology, Bangladesh Agricultural University, Mymensingh, Biotechnology
Laboratory, Bangladesh Institute of Nuclear Agriculture, Mymensingh and
Molecular Biology Laboratory, Department of Biochemistry and Molecular Biology,
Xiamen University, Fujian, China during the period of 2009-2012. Thirty eight
soybean genotypes of soybean were screened at 80 mM NaCl in 1½ strength MS
media. Through multivariate analysis, 21, 16, 31.5 and 31.5% of the genotypes were
categorized as tolerant, moderate tolerant, moderate susceptible and highly
susceptible, respectively. This grouping was verified at molecular levels by salt
tolerant linked 4 SSR markers. It was found that Shohag, Asset 93, AGS 313, MACS
57 and AGS 66 were more tolerant than others. Selected soybean genotypes (10) from
the different categories were further assessed by 0, 40, 80, 120 and 160 mM NaCl
levels under in vitro condition. It was found that shoot length, fresh shoot weight,
dry shoot weight, fresh root weight and dry root weight were significantly reduced
with the increasing of salinity levels. Tolerance index, proline content, soluble sugar,
soluble protein, superoxide dismutase, ascorbate peroxidase, catalase, chlorophyll a,
chlorophyll b, total chlorophyll, carotenoids anthocyanin, potassium ion in leaf were
higher in genotype of Shohag comparing to susceptible genotype Asset 95 under
different salinity levels. On the other hand, water uptake capacity, malondialdehyde,
hydrogen peroxide, sodium content in leaf, sodium potassium ration etc. were
higher in Asset 95 confers the tolerance of salinity in Shohag and susceptibility in
Asset 95. Expression of AtNHX1 and ThNHX1genes were also study under different
salinity levels. Highest expression of AtNHX1 and ThNHX1 were found at 150 and
100 mM salinity levels, respectively. AtNHX1 and ThNHX1 were cloned from the
Arabidopsis thaliana and Thellungiella halophila, respectively following the Gateway
cloning system. The cloned AtNHX1 and ThNHX1 genes will help to develop
transgenic salt tolerant soybean in future.