Revisiting the Proliferated Seed Cones in Larix kaempferi Reveals a Growth Arrest Plasticity.

Abstract

In angiosperms, such as Arabidopsis, silique removal can reverse developmental arrest and reactivate inflorescence meristems, illustrating that post-fertilization growth cessation is a plastic process rather than terminal differentiation. However, it remains unclear whether a similar growth arrest plasticity occurs in conifers, where mature seed cones typically undergo terminal differentiation as determinate structures. In this study, we analyzed the proliferated seed cones of Larix kaempferi, which exhibited vegetative shoots sprouting from their central axes. We collected and examined both the proliferated and normal seed cones from a second-generation seed orchard. The proliferated seed cones were longer, produced more seeds, had a smaller seed scale spacing, and displayed enhanced secondary growth compared to normal seed cones. Our analysis suggested that the proliferated seed cones underwent a transition from reproductive to vegetative growth after seed production, indicating that proliferative arrest in these cones can be disrupted. Based on structural and developmental comparisons with Arabidopsis thaliana, the proliferated seed cones exhibit unexpected plasticity: their growth arrest is reversible rather than terminal, similar to silique-removal-induced meristem reactivation in Arabidopsis. This suggests that conifer cones retain the ability for delayed differentiation, not only offering new insights into conifer development but also a potential conifer model for studying reproductive-to-vegetative phase transition.