Figure 1.

Membrane localization of the Arabidopsis SOS1 protein. Microsomal membranes from plants grown in the absence of salt were fractionated over 5% to 45% (w/v) Suc gradients, and 1-mL fractions were collected. Membrane protein (18 μg) from the indicated fractions was separated by 10% (w/v) SDS-PAGE and transferred to nitrocellulose membranes. Unless indicated, immunological detection was carried out on fractions isolated from shoots of wild-type plants. Antibodies used from top to bottom: SOS1, SOS1 (membrane protein isolated from roots), SOS1 (membrane protein isolated from shoots of sos1 mutant plants), V-ATPase (VMA-E, vacuolar H⁺-ATPase E-subunit; Dietz and Arbinger, 1996), PPase (vacuolar H⁺-pyrophosphatase; PAB-HK antibody; Kim et al., 1994), Calreticulin (Nelson et al., 1997), P-ATPase (plasma membrane H⁺-ATPase; PMA1 isoform; Pardo and Serrano, 1989), and HKT1 (plasma membrane K⁺/Na⁺ cotransporter; Su et al., 2003). Bands were detected by chemiluminescence. Molecular masses of the bands are indicated.