Antagonistic interactions between cytokinin and gibberellin during initial stem growth and leaf structure of royal poinciana [Delonix regia (Bojer ex. Hook.) Raf.]

Gibberellin (GA) and cytokinin (CK) signaling play antagonistic roles in leaf development and secondary plant growth. In the current study, we investigated the effects of changes in the balance of CKs and GAs on the development and leaf and stem morpho-anatomy of Delonix regia (Bojer ex. Hook.) Raf. seedlings. The balance of CKs and GAs was modified by the exogenous application of plant growth regulators (PGRs), individually or in combination. After 30 days of daily PGR applications, the growth and the morpho-anatomy of the leaf and stem were assessed. CKs and GAs have antagonistic effects on the development of D. regia. Seedlings treated with GA showed a significant increase in height, while the application of CK led to greater formation of axillary shoots, altering the architecture of the plants. GA inhibited almost all CK responses, although a negative reciprocal interaction was observed in some growth parameters. The treatments in which GA was applied showed an increase in leaf length. However, these plants presented a reduction in leaf tissue thickness and the stem cambial band. In contrast, plants treated with CK and paclobutrazol had thicker leaf blades and more prominent radial growth of the stem, with a higher proportion of secondary xylem. Our results suggest a mutual antagonistic interaction between GA and CK in D. regia and contribute to understanding how the balance between these two classes of phytohormones modulates the structure and development of plant lateral organs.