|Van't Hof, J - BROOKAVEN NATIONAL LAB|
Submitted to: Journal of New Seeds
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 3, 2005
Publication Date: April 1, 2005
Citation: Saha, S., Van'T Hof, J. 2005. Cotton fiber cells are arrested at G1 stage. Journal of New Seeds. 7:1-8. Interpretive Summary: A cotton fiber cell normally elongates as a single ovule epidermal cell. Regulation of cell division during the early stages of fiber development may trigger specific epidermal cells to elongate into what are called fibers. The interphase of dividing cells may broadly be grouped under three cell cycle phases: the presynthesis phase (G1), the DNA-synthesis phase (S) and the postsynthesis phase (G2). Very little information is available on the cell cycle of a fiber cell. The primary objective of this study was to identify the phase in which division of cotton fiber cells stops and elongation begins. We exploited our recent discovery that fiber cells can divide in order to determine the stage of the cell cycle at which fiber cells stop dividing and begin elongation. If cell division stops and fiber elongation begins when the cell is in the G1 phase, treatment with an inhibitor of DNA replication would prevent cell division and reduce the frequency of multi-celled fibers; however, if elongation begins in the G2 phase, multi-celled fibers would be produced. When the inhibitor 5-aminouracil (5-AU) was added to ovule culture medium, we observed that 98% of the fiber cells in an ovule did not divide. Our results demonstrated that cotton fiber cell division stops in the G1 cell cycle phase and begins to elongate. We also observed that in developing fiber cells, cell division and cell elongation are independent events.
Technical Abstract: Regulation of cell cycle genes during the very early stages of cotton fiber development triggers specific epidermal cells in the ovule to stop cell division and then elongate into fiber cells. The objective of this study was to identify the cell cycle phase in which cotton fiber cells are arrested before beginning elongation and the different cellular mechanisms that may control the initial phases of fiber development. We exploited the recent discovery that fiber cells can divide to determine the cell cycle stage at which fiber cell elongation occurs. If elongation begins when the cell is in the G1 phase of the cell cycle, treatment with an inhibitor of DNA replication would prevent cell division and reduce the frequency of multi-celled fibers. On the other hand, if elongation begins from the G2 phase after the completion of DNA replication during S phase of the cell cycle, multi-celled fibers still would be produced. The 5-aminouracil (5-AU), an inhibitor of DNA replication, added to ovule culture medium, was used to identify the cell cycle phase in which the developing fiber cells were arrested. Our results demonstrated that cotton fiber cells were arrested at the G1 stage. The unique pattern of cell wall formation resulting in multicellular fiber demonstrated that an ovule epidermal cell regulates the morphogenesis or polarity in fiber at a very early stage of development by controlling cell wall formation only perpendicular to the long axis of the fiber. We also observe no branched fibers from ovules grown under any condition (in vitro or in vivo). The lack of branched fibers indicated polarized fiber growth was fixed.