Also,
550 ng of [13C6]-IAA (Cambridge Isotopes, Inc.) was
added as an internal standard for the GC-MS-SIM
quantification. After 60 h of constant shaking at 4 1C
in the dark, the methanolic extracts were filtered
through 0.45 and 0.22 mm cellulose acetate membranes
(Millipores) and then passed through a Sep-
Pak C-18 (Waterss) cartridge. After filtration,
eluates were reduced to dryness in a speed vacuum
concentrator (Speed Vac, Hetos, CT 100) and the
residues redissolved in 100 mL acid water (ultrapure
water+0.2% formic acid, pH 3.0).