Endopolyploidy and ploidy stability during protocorm-like body morphogenesis and regeneration in Cattleya tigrina A. Richard

Background: Protocorm-like bodies (PLBs) represent a major morphogenic pathway in orchids and are characterized by cellular reprogramming, tissue differentiation, and developmental reorganization. Although PLB formation is widely explored for orchid micropropagation, endopolyploidy dynamics during PLB morphogenesis remain poorly understood. Aims: This study aimed to characterize endopolyploidy patterns and evaluate nuclear DNA content maintenance during PLB morphogenesis and plant regeneration in *Cattleya tigrina*. Methods: Basal leaf explants were cultured under PLB-inducing conditions *in vitro*. Morphological and histological analyses were performed throughout PLB development, while nuclear DNA content was estimated by flow cytometry in leaf regions, PLBs at successive developmental stages, and regenerated plants. Results: The leaf base was the most responsive region for PLB induction, showing intense cell proliferation and meristematic activity. Flow cytometric profiles consistently revealed 2C, 4C, and 8C nuclear DNA peaks, indicating endopolyploidy in somatic tissues. PLBs exhibited transient shifts in ploidy distribution during active proliferation phases, particularly at intermediate developmental stages, when 4C nuclei became predominant. Regenerated plants maintained nuclear DNA contents comparable to the original explants. Conclusions: Endopolyploidy is an intrinsic and developmentally regulated feature of PLB morphogenesis in *Cattleya tigrina*. PLB-mediated regeneration maintained overall nuclear DNA content under the evaluated *in vitro* conditions.