*2.6. Cold Stress Treatment of Transgenic Lines*

The Agrobacterium transformed with pCAMBIA1304-*PebHLH56*p were shaken at 28 ◦C in YEB medium containing Kan and Rif antibiotics, respectively, and added to an *Arabidopsis* transgenic infiltration solution (1/2 MS, 50 g/L) to OD 600 = 0.8–1.0. Inflorescence impregnation was used to transform *Arabidopsis thaliana*. Eight transgenic lines have been obtained. Then three plants from each of the two lines in the T2 generation were cultured for cold stress treatment [8]. The 14-day-old transgenic *Arabidopsis* was treated in an incubator at 4 ◦C for 0, 24, and 36 h, respectively [3].

#### *2.7. Detection of GUS Activity*

The transgenic *Arabidopsis* with pCAMBIA1304-*PebHLH56p* under normal and cold stress were GUS stained. For GUS staining, seedlings of two lines were incubated in X-Gluc solution for 24 h at 37 ◦C [45,49]. GUS enzyme activity was determined by 4-methylumbel ureylglucuronide fluorometry [50].
