ORGANOGENESIS AND NUCLEAR DNA CONTENT IN PINE TISSUE CULTURES (CYTOPHOTOMETRY, PROPAGATION, APICAL MERISTEM)

Methods for cell and tissue culture of forest trees are continually being refined. Available techniques are increasing as are their applications. Despite these advances, little is known of the effects of the issue culture process on the genetic condition of tissues and regenerated plants. To investigate the genetic condition of loblolly pine (Pinus taeda L.) tissue cultures, nuclear DNA content was measured by microspectrophotometry.;Pines can be propagated in vitro from embryonic tissues, but explants from mature trees have proven recalcitrant. Although callus cultures can be established from older trees with relative ease, whole plants have not been regenerated from pine callus cultures. Shoot apical meristem cultures were established using apices from seedlings and brachyblasts. A method for vegetative propagation of mature pines from brachyblast culture is suggested.;Nuclear DNA content was quantitatively measured in cells from callus cultures initiated from embryonic and megagametophytic explants. Buds regenerated on media containing cytokinin as the sole exogenous growth regulator contained nuclei with DNA contents in the diploid range. When auxin was added to media, DNA contents in regenerated buds were in the diploid and tetraploid range. Heterogeneity of nuclear DNA content was greatest in callus from diploid embryos, ranging from diploid amounts to amounts in excess of that in tetraploid cells. Callus from haploid explants became mixoploid, with approximately one-quarter of the cell population possessing diploid amounts of DNA. These results demonstrate that, for a given species, alteration of medium composition can affect the degree of genetic instability introduced during the tissue culture phase of plant regeneration programs.