DNA content and expression of genes related to cell cycling in developing Gossypium hirsutum (Malvaceae) fibers

The cell cycle in cotton (Gossypium hirsutum) fibers is poorly understood. The objective of this study was to evaluate the cell cycle status and DNA content in developing cotton fibers. The DNA content and cell cycle distribution in fiber and hypocotyl cells were determined by flow cytometry. Expression levels of minichrosomal maintenance protein (mcm), cyclin B, and a retinoblastoma-like protein (rb) genes were determined with real-time PCR in fibers and dividing and nondividing tissues. No endoreduplication occurred, nor did genome size or percentage of G1-phase nuclei differ between hypocotyls and fibers. Approximately 13 and 17% of fiber nuclei were in the S phase in 14 days after anthesis (d) fibers and 25 d fibers, respectively. The mcm and cyclin B were expressed at higher levels in fibers than in mature leaves, but expression levels in fibers were less than 15% of meristematic tissues. Rb was expressed in fibers at levels less than 50% of mature leaves or meristematic tissues. Based on an apparent increase in S-phase cells as fibers mature and the low level of expression of genes associated with cell cycle progression, we conclude that S-phase arrest occurs in developing cotton fiber.