Effect of Light and Cytokinin Modulators on Adventitious Shooting in Melia volkensii Gürke

Adventitious shoot regeneration in woody species is regulated by interactions between plant growth regulators, endogenous hormone metabolism, and environmental cues such as light quality. Here, we investigated the effects of thidiazuron (TDZ) and the cytokinin oxidase/dehydrogenase (CKX) inhibitors INCYDE and phenyladenine (PA), in combination with different light spectra, on morphogenesis in Melia volkensii leaf explants. TDZ induced the highest frequencies of callus formation and adventitious shoot regeneration, particularly under white light. INCYDE promoted localized regeneration responses, including activation of dormant meristematic regions in secondary leaf axils, whereas PA showed limited regeneration efficiency. Light quality significantly influenced morphogenesis, with white and blue light favoring organized shoot development, while red and far-red light suppressed shoot regeneration and promoted callus formation. Cytokinin profiling revealed treatment-dependent shifts in endogenous cytokinin composition, most notably in isopentenyladenine (iP)-type cytokinins, which is consistent with altered cytokinin degradation dynamics. Cis-zeatin-type cytokinins were abundant across treatments, likely reflecting regulation associated with in vitro culture conditions. These findings indicate that cytokinin metabolism and light quality jointly influence organogenic competence in Melia volkensii Gürke, providing a physiological basis for optimizing regeneration strategies in woody plants. This study provides the first integrated analysis of cytokinin-modulating compounds and light spectra on adventitious shoot regeneration in Melia volkensii. The findings establish a physiological basis for improving regeneration protocols in recalcitrant woody species and support future biotechnological applications, including genetic improvement and advanced propagation strategies.