Flower Formation in Excised Tobacco Stem Segments: III. Deoxyribonucleic Acid Content in Stem Tissue of Vegetative and Flowering Tobacco Plants.

A method has been developed that extracts DNA from stem tissue of flowering tobacco plants, Nicotiana tabacum cv. Wis. 38. The DNA content of stem tissue from a flowering tobacco plant is correlated with its capacity to flower in vitro. Stem segments known to form 100% floral buds contain 10 times more DNA per gram fresh weight than segments that form 5% floral buds and 95% vegetative buds, and in the uppermost 28 centimeters of flowering tobacco plant stems the DNA content decreases roughly in parallel with the floral gradient.((3)H)-Thymidine incorporation into DNA in the internodes is inhibited by attached leaves in flowering tobacco plants but promoted in vegetative plants. Low indoleacetic acid concentrations (2.8 and 5.7 mum) inhibit DNA synthesis in internodes of defoliated stems of flowering tobacco plants to the same extent as attached leaves, whereas the same concentrations of indoleacetic acid promote DNA synthesis in internodes of defoliated stems of vegetative plants. The optimal concentration (11.4 mum) of indoleacetic acid supplied to defoliated stems of vegetative plants increased the rate of DNA synthesis to 4 times the rate in defoliated stems without indoleacetic acid treatment. This increase more than compensates for the promotion of DNA synthesis by the young leaves. Thus, the opposite effects of young leaves on DNA synthesis in internodes of flowering and vegetative tobacco plants may be related to their auxin content.