The role of gibberellin, abscisic acid, and sucrose in the regulation of potato tuber formation in vitro

The effects of plant hormones and sucrose (Suc) on potato (Solanum tuberosom L.) tuberization were studied using in vitro cultured single-node cuttings. Tuber-inducing (high Sue) and -noninducing (low Suc or high Suc plus gibberellin [CA]) media were tested. Tuberization frequencies, tuber widths, and stolen lengths were measured during successive stages of development. Endogenous GAs and abscisic acid (ABA) were identified and quantified by high-performance liquid chromatography and gas chromatography-mass spectrometry. Exogenous GA(4/7) promoted stolen elongation and inhibited tuber formation, whereas exogenous ABA stimulated tuberization and reduced stolen length. Indoleacetic acid-containing media severely inhibited elongation of stolons and smaller sessile tubers were formed. Exogenous cytokinins did not affect stolen elongation and tuber formation. Endogenous GA(1) level was high during stolen elongation and decreased when stolen tips started to swell under inducing conditions, whereas it remained high under noninducing conditions. GA(1) levels were negatively correlated with Suc concentration in the medium. We conclude that GA(1) is likely to be the active CA during tuber formation. Endogenous ABA levels decreased during stolen and tuber development, and ABA levels were similar under inducing and noninducing conditions. Our results indicate that CA is a dominant regulator in tuber formation: ABA stimulates tuberization by counteracting GA, and Suc regulates tuber formation by influencing CA levels.