Figure 1

Elevated endogenous auxin level in the basal end of explants inhibits shoot organogenesis of ‘Carrizo’ citrange stem segments. In all pictures, explants are arranged with the apical end facing up and the basal end facing down. (a) An internodal stem explant with a blunt basal end formed shoot primordia on the apical end, but shoot initiation was repressed on the basal end. (b) When N-1-naphthylphthalamic acid (NPA) was applied to blunt-cut internodal stem explants, shoot primordia formed on both the apical and basal ends of the explant. (c) GUS-stained DR5::uidA blunt-cut internodal segments show a blue color at the basal end, which is indicative of an elevated auxin level. (d) When NPA was applied to DR5::uidA blunt-cut internodal segments, a blue color was evenly distributed across the explant, indicating polar auxin transport was inhibited. (e) An internodal stem explant with a slanted end had shoots initiated from the upper region of the cut (sub-apical). (f) When NPA was applied to slant-cut internodal stem explants, shoot primordia formed at both the apical and basal ends of the cut. (g) GUS-stained DR5::uidA slant-cut internodal segments show a blue color at the basal end of the cut, indicating elevated auxin in these cells due to polar auxin transport. (h) When NPA was applied to DR5::uidA slant-cut internodal segments, a blue color was evenly distributed across the explant, indicating that polar auxin transport was inhibited.