Evaluation of endopolyploidy patterns in selected Capsicum and Nicotiana species (Solanaceae)

Abstract

Endopolyploidy has arisen countless times in angiosperms, and endopolyploidisation is an important genetic feature in many plant species. It is generated through a process called endoreduplication, where a mitotic cell cycle shifts into an endocycle, and DNA replication occurs without chromosome separation and cytokinesis. It has been well established that endopolyploidy plays a vital role during plant growth and development and in various stress responses. Many agriculturally important plant families are polysomatic, including the Solanaceae. To better understand and characterise polysomatic species within the Solanaceae, we studied endopolyploidy in mature vegetative and reproductive organs (root, stem, lower leaf petiole, lower leaf lamina, flower pedicel, calyx, corolla, pistil and stamen tissue) of representative diploids within the genus Capsicum, i.e. C. annuum, C. baccatum, C. chinense and diploid and tetraploids within the genus Nicotiana, i.e. N. rustica (4x), N. sylvestris (2x) and N. tabacum (4x), by means of flow cytometry. The presence of 2C–16C nuclei (rarely 32C) was detected, and the degree of endopolyploidisation was expressed using four different parameters for each organ analysed. In vegetative organs, the endoreduplication index (EI) reached a maximum of 0.84 on average for roots of C. baccatum, whereas the lowest values (EI < 0.10) were detected in the leaf lamina of the same species. Among the reproductive organs investigated in N. tabacum, EI values for pistils were higher than for stamens. When the diploid and polyploid Nicotiana species were compared, diploid N. sylvestris possessed a higher endopolyploidy level than the polyploids N. rustica and N. tabacum. In this study, we also determined genome size for each of the investigated species, which ranged from 5.51 picograms (pg) in N. sylvestris to 10.43 pg in N. rustica.