Absract:

Cytokinins (CKs) exist in various forms within potato plants, among which the active CKs account for only a minute fraction but play crucial roles in tuber development. In the present study, in vitro potato stolons were exposed to graded concentrations of active CK N⁶-(Δ²-isopentenyl)-adenine (2ip) and CK-biosynthesis inhibitor lovastatin, and the phenotypic and endogenous phytohormone dynamics during tuber development were investigated. The results showed that low 2ip concentrations promoted tuberization, with 0.1 μM 2ip exhibiting the strongest inductive effect. The initial time of tuberization was advanced, and the tuberization rate, tuber fresh weight, and tuber diameter significantly increased. With increasing 2ip concentrations, higher levels (>50 μM) inhibited tuberization and markedly elevated the length-to-width ratio of tubers. Inhibiting CK biosynthesis by lovastatin also inhibited tuberization, and even induced the formation of abnormal tubers. Treatment with 0.1 μM 2ip shifted the endogenous hormone balance toward a state that favors tuber formation and development. Levels of active CKs (iP, tZ, and DHZ), IAA, and SA significantly increased, whereas the contents of total jasmonates (JA, JA-Ile, and cis-OPDA), ABA, and inactive CKs (iPR and cZR) decreased. The ratios of active CKs to GA₃, ABA, or JA, as well as the IAA/ABA and IAA/GA₃ ratios, significantly increased. Inhibition of CK biosynthesis elicited changes in CKs, JAs, and ABA levels, as well as in the associated phytohormone ratios, that were opposite to those observed with 0.1 μM 2ip treatment. Thus this study revealed the specific physiological roles of active CKs in tuber development and provided insights into the mechanisms of tuber development regulated by CKs.