Morphogenesis in tobacco subepidermal cells: Putrescine as marker of root differentiation

We have used the tobacco thin cell layer in vitro system to evaluate changes in polyamine titers as correlated with root differentiation and with variations in external pH during culture. We show that root differentiation in this system depends on both a rise in putrescine titers and a drop of pH, each of these two factors acting independently. With respect to polyamine titers, the most dramatic changes occur in the levels of putrescine liberated from perchloric acid-soluble conjugates. These titers increase from day 0 to day 7 of culture, reaching almost 2000 nmol g^-1 fresh weight. Inhibition of putrescine biosynthesis prevents root initiation, while exogenous putrescine supply reverses this effect. We conclude that putrescine is a good marker for root differentiation.