Potassium iodide promotes bud regeneration from the apical root sections of shallot plants

Abstract

The apical root sections of Allium ascalonicum plants respond to a callus inducing treatment by forming callus from the root apical meristem. It has been shown in Arabidopsis thaliana that balance between superoxide and hydrogen peroxide (H2O2) in the root tip determines root meristem size by controlling the transition from cell proliferation to differentiation. Hence, the increased size of root meristem may affect callus formation and subsequent bud regeneration from the root-tips. To test this hypothesis, in vitro-grown shallot plants were pretreated with aqueous solutions of H2O2 (100, 500 or 1000 μM) or potassium iodide (KI, 1 or 10 mM) for 24h. Plants incubated in water were used as a control. The apical root sections (1 cm) isolated from these plants were cultivated on callus induction medium, supplemented with 5 μM 2,4-D + 5 μM BA, for 8 weeks and then on regeneration induction medium, containing 5 μM BA, for 4 weeks. Obtained results indicate the significant impact of KI on de novo bud regeneration. Explants treated with 1 mM KI regenerated buds with significantly higher frequency (83.6% vs. 25.2%) and the mean bud number (6.19 vs. 0.21) compared to the control. The frequencies of bud regeneration and the mean bud numbers obtained for H2O2-treated explants were significantly lower compared to KI-treated explants (43.5% 52.0% and 1.0-2.3, respectively). Assuming that H2O2 decreases size of the root meristem, as was shown in Arabidopsis, the results obtained in this work suggest that KI, a H2O2 scavenger, increased bud-forming capacity presumably by increasing the size of root meristem.