Abstract
Differentiation of a protocorm-like body (PLB) in vitro from the outer tissue (OT) of Cymbidium PLBs was studied. Cell division frequency was high in the first to third layers of OT explants. The frequency of anticlinal cell division was dominant in outer cell layers, whereas both periclinal and anticlinal cell divisions occurred in the inner cell layers. Cell division frequency in a group of dividing cells was activated in the center of a protuberance (PLB initials). These results trace the process of globular PLB formation. There were differences between NAA and BA effects on the cells of OT cultured tissue. Cell division activity was high in the BA treatment whereas dividing cells were not observed in most cultures of NAA treatment. The cell size was larger in NAA-treated explants ; it was smaller in BA-treated ones. These results show that BA stimulated cells division whereas NAA affected cell maturation. The nuclear DNA contents were stable and constant on both hormone-free and BA supplemented media. In NAA-treated explants the DNA contents changed gradually with time toward the levels of 8c and 16c. NAA did not inhibit DNA synthesis but inhibit mitosis. NAA may affect the cell cycle between the S and M phases. The data on the cell division activity and the cell size indicate that plant growth regulators also may affect the length of the G1 phase and induce somaclonal variations during plant culture distorting the cell cycle.
