Histological analysis

Histological staining was conducted in the tobacco at growth period with three biological replicates. The procedure was as follows: 1) fixed the stems in the FAA solution (70% ethanol: glacial acetic acid: formaldehyde; 90: 5: 5, v/v) and embedded them in the frozen sectioning medium (OCT; Thermo Scientific, Waltham, MA); 2) cut the embedded stems into slices and put the slices on the slides; 3) stained the slides with phloroglucinol solution for 2 min; 4) soaked the slides in 50% (v/v) HCl; 5) put coverslips on the slides and wiped the slides with lens paper; 6) examined the slides with optical light microscope [47].