Determination of endogenous levels of abscisic acid (ABA)
Cucumber plants were immediately frozen using liquid N and
stored at
−80 ◦C before use. Samples were extracted three times
using 80% methanol at 4 ◦C overnight. Methanol was combined
and evaporated in vacuo to get an aqueous residue. The aqueous
solution with deuterium-labeled ABA (d6-ABA) as an internal standard
was adjusted to pH 7 with 1 N NaOH and then partitioned
against ethyl acetate three times. After partitioning, the aqueous
phase was adjusted to pH 2 with 1 N HCl and partitioned against
ethyl acetate three times. The organic phase was combined and
evaporated to dryness. Silica gel thin layer chromatography with
the solvent system of n-hexane:chloroform:ethyl acetate:acetic
acid = 20:8:20:5 (v/v/v/v) was introduced to purify the samples.
The zone corresponding to that of ABA in the chromatogram was
scraped off and extracted with ethyl acetate. After the ethyl acetate
evaporated, a partially purified sample was methylated with ethereal
diazomethane. The total amounts of endogenous ABA were
determined using gas chromatography–mass spectrometry (GCQ,
Finnigan MAT Co.). The retention times of cis, trans-ABA and trans,trans-ABA were 10.1 and 11.0 min, respectively. The areas of mass
spectrometry fragments at m/z 190 (native ABA) and 194 (d6-ABA)
were used for quantification.
Determination of endogenous levels of abscisic acid (ABA)
Cucumber plants were immediately frozen using liquid N and
stored at
−80 ◦C before use. Samples were extracted three times
using 80% methanol at 4 ◦C overnight. Methanol was combined
and evaporated in vacuo to get an aqueous residue. The aqueous
solution with deuterium-labeled ABA (d6-ABA) as an internal standard
was adjusted to pH 7 with 1 N NaOH and then partitioned
against ethyl acetate three times. After partitioning, the aqueous
phase was adjusted to pH 2 with 1 N HCl and partitioned against
ethyl acetate three times. The organic phase was combined and
evaporated to dryness. Silica gel thin layer chromatography with
the solvent system of n-hexane:chloroform:ethyl acetate:acetic
acid = 20:8:20:5 (v/v/v/v) was introduced to purify the samples.
The zone corresponding to that of ABA in the chromatogram was
scraped off and extracted with ethyl acetate. After the ethyl acetate
evaporated, a partially purified sample was methylated with ethereal
diazomethane. The total amounts of endogenous ABA were
determined using gas chromatography–mass spectrometry (GCQ,
Finnigan MAT Co.). The retention times of cis, trans-ABA and trans,trans-ABA were 10.1 and 11.0 min, respectively. The areas of mass
spectrometry fragments at m/z 190 (native ABA) and 194 (d6-ABA)
were used for quantification.
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