Figure 6. Effect of nitrate or ammonium ion on AtSIZ1 transcript and AtSIZ1 protein levels.

(a, b) Effect of nitrate or ammonium ion on the AtSIZ1 transcript level. The leaves (a) and roots (b) of WT plants were treated with 5 mM KNO3 or (NH4)2SO4, and the transcript level of AtSIZ1 was examined by real-time RT–PCR. Results are expressed as means±s.e. (n=3). (c) Transgenic plants overexpressing HA₃-AtSIZ1. Total proteins were extracted from transgenic plants harbouring 35S-HA₃-AtSIZ1, and the HA₃-AtSIZ1 protein was detected by immunoblotting with an anti-HA antibody. Numbers within parentheses indicate independent transgenic lines. Transgenic line (number 2) with high HA₃-AtSIZ1 protein was chosen for further experimentation. (d) Effect of nitrate or ammonium sources on AtSIZ1 stability transgenic plants were treated with 5 mM KNO3 or (NH4)2SO4. The HA₃-AtSIZ1 protein levels were detected by immunoblotting with an anti-HA antibody. Tubulin levels were used as loading controls. Numbers under lanes indicate relative intensities.