2.4. 2-D DIGE analysis
2-D DIGE gels of each group of T and NT soybean leaf protein
species were prepared in quadruplicate. Protein samples were
labelled according to the manufacturer's protocol for minimal
labelling (GE Healthcare). The precipitate of the protein was
resolubilised in a lysis buffer (7 M urea, 2 M thiourea, 4% (m/v)
CHAPS, and 20 mM Tris, pH 8.8, without reducing agent), prior
to dye labelling. For labelling with CyDye DIGE Fluor minimal
dyes, 50 μg (pH range 4–7) of each sample was labelled with
400 pM CyDye DIGE Fluor minimal dyes (GE Healthcare) and
incubated on ice in the dark for 30 min. For each replicate
reaction, one sample was labelled with Cy3, the other sample
with Cy5, and the internal standard with Cy2. Two T and two
NT leaf samples were labelled with Cy5 and Cy3, respectively.
For the third replicate, the CyDyes were swapped to correct for
any bias introduced by the different fluorescence characteristics
of acrylamide at the different excitation wavelengths of
Cy3 and Cy5. The internal standard, labelled with Cy2,
consisted of a pooled sample comprised of equal amounts of
each T and NT leaf sample used for each quadruplicate. The
Cy2 dye itself is considered to be a normaliser [23], increasing
the statistical confidence for quantification among different
gels. The reactions were quenched by adding 1 μL of 10 mM
lysine followed by incubation for an additional 10 min. Each
labelled protein sample was diluted with rehydration