Endopolyploidy pattern in Corydalis early spring geophytes

Abstract Endopolyploidy, a condition where the nuclear ploidy level of various cells and tissues of an organism increases, is present in diverse plant species. Endopolyploidy contributes to cell enlargement, increases gene expression, and accelerates growth, hence it is associated with cell differentiation, development, and physiology of plants. However, the occurrence of this phenomenon in plants and the diversity of functional roles of endopolyploidy remains poorly understood. In this study, we have used flow cytometry to perform a detailed survey of the extent and patterns of endopolyploidy in various organs of two early spring geophytes, Corydalis cava and C. solida. We identified between 2C and 32C ploidy classes. Most of the stem samples contained only endopolyploid cells (4C – 32C) in both species. The endoreduplication index varied between 0.34 (leaf lamina) and 2.45 (basal part of the stem). Both species showed a similar level of endopolyploidy, and the endopolyploidy index exceeded 1.5 in the root, tuber, stem, peduncle, petiole, and scale leaf of at least one species. The endopolyploidy index differed in leaf lamina, ovary, style, and stamen between two species. Compared to other angiosperm groups, Corydalis may be included into highly endopolyploid plants. Geophytism is generally associated with high genome size, but this is not the case in Corydalis. We hypothesised that high endopolyploidy level found in Corydalis may compensate for the low genome size and thus help to promote plant growth during the early spring.