Figure 3
Auxin concentrations are negatively correlated with shoot organogenesis on ‘Carrizo’ citrange stem segments. In all pictures, explants are arranged with the apical end facing up and the basal end facing down. (a) Untreated explants produced calli at both ends and developed shoots from the apical end. (b) GUS-stained DR5::uidA explants had higher GUS expression at the basal end due to polar auxin transport. (c) Explants treated with 0.5 mg L-1 exogenous IAA had enhanced callus production from both ends and had reduced shoot organogenesis. (d) GUS-stained DR5::uidA explants had elevated GUS activity in the entire explant because of exogenous application of auxin (0.5 mg L-1 indole-3-acetic acid (IAA)). (e) Explants incubated with MS medium (wash) for 2 h to deplete endogenous auxin produced shoots from both the apical and basal ends. (f) GUS-stained DR5::uidA explants had no detectable GUS activity after the wash. (g) Shoot organogenesis was negatively correlated with auxin concentration: ‘0’—no auxin was added to the solid MS medium; ‘0.5’—0.5 mg L-1 IAA was added to the solid medium; MS incubated—explants were washed with MS liquid medium for 2 h to deplete endogenous auxin.
