High frequency of cytomixis observed at zygotene in tetraploid Lippia alba

Abstract

Lippia alba (Verbenaceae) is an aromatic shrub recently described as a new tropical polyploid species with five distinct chromosome numbers (2n = 30, 38, 45, 60, and 90) with 2n = 30, 45, and 60 being the most frequent ones. Cytomixis is a cellular process known as the migration of genetic material mainly between meiocytes through cytoplasmic connections or cytomictic channels. This phenomenon has been reported in various plant families such as Leguminosae, Brassicaceae, Poaceae, Apocynaceae, Liliaceae, Rutaceae, and others. The transference of genetic material between pollen mother cells (PMCs), by cytomictic channels, induces the formation of unbalanced and unreduced (2n) gametes, and is considered a possible source of aneuploid and polyploid plants. Here, we describe for the first time, the occurrence of cytomixis in meiotic cells of L. alba (tetraploid cytotype) analyzing data obtained from meiotic behavior assays. In addition, the pollen size and viability were also evaluated. A high index of irregularities during meiosis was observed as well as unviable pollen with heterogeneous size. Approximately 80 % of zygotene cells showed genetic material exchange. Considering that L. alba shows different chromosome numbers, the contribution of cytomixis to cytotypes formation is also discussed.