Figure 4.

MdHXK1 improves stability and Na⁺/H⁺ exchanger activity of MdNHX1. A, Cell-free degradation assay of recombinant protein MdNHX1-GST or MdNHX1^S275A-GST in the protein extract of transgenic apple calli as labeled. Protein samples of each transgenic apple calli were extracted in degradation buffer. The levels of MdNHX1-GST or MdNHX1^S275A-GST were visualized by immunoblotting using an anti-GST antibody. B, Quantification of MdNHX1-GST protein or MdNHX1^S275A-GST levels as in (A). C, Na⁺/H⁺ exchanger activity of vacuolar membrane proteins in 35S::MdNHX1 and 35S::MdNHX1^S275A transgenic calli after transformation with 35S::MdHXK1 or anti-MdHXK1-RT vector. Each value represents the mean ± sd from three separate experiments. n.s., P > 0.01; *, P < 0.01; **, P < 0.001.