Effects of benzyladenine and alpha - Naphthaleneacetic acid on cell division and nuclear DNA contents in outer tissue of Cymbidium explants cultured in vitro

Differentiation of a protocorm-like body (PLB) in vitro from the outer tiss ue (OT) of Cymbidium PLBs was studied. Cell division frequency was high in the first to third layers of CT explants. The frequency of anticlinal cell division was dominant in outer cell layers, whereas both periclinal and ant iclinal cell divisions occurred in the inner cell layers. Cell division fre quency in a group of dividing cells was activated in the center of a protub erance (PLB initials). These results trace the process of globular PLB form ation. There were differences between NAA and BA effects on the cells of OT cultur ed tissue. Cell division activity was high in the BA treatment whereas divi ding cells were not observed in most cultures of NAA treatment. The cell si ze was larger in NAA- treated explants; it was smaller in BA-treated ones. These results show that BA stimulated cells division whereas NAA affected c ell maturation. The nuclear DNA contents were stable and constant on both h ormone-free and BA supplemented media. In NAA-treated explants the DNA cont ents changed gradually with rime toward the levels of 8c and 16c. NAA did not inhibit DNA synthesis but inhibit mitosis. NAA may affect the c ell cycle between the S and M phases. The data on the cell division activit y and the cell size indicate that plant growth regulators also may affect t he length of the G1 phase and induce somaclonal variations during plant cul ture distorting the cell cycle.