Inverse Relationship between Polyamine Levels and the Degree of Phenotypic Alteration Induced by the Root-Inducing, Left-Hand Transferred DNA from Agrobacterium rhizogenes.

Floral induction in plants is a paradigm for signal perception, transduction, and physiological response. The introduction of root-inducing, left-hand transferred DNA (Ri T-DNA) into the genomes of several plants results in modifications of flowering (D Tepfer [1984] Cell 47: 959-967), including a delay in flowering in tobacco ( Nicotiana tabacum ). Conjugated polyamines are markers for flowering in numerous species of plants. In tobacco their accumulation is correlated with the onset of flowering (F Cabanne et al. [1981] Physiol Plant 53: 399-404). Using tobacco, we have explored the possibility of a correlation between the expression of Ri TL-DNA and changes in polyamine metabolism. We made use of two levels of phenotypic change, designated T and T′, that retard flowering by 5 to 10 and 15 to 20 days, respectively. We show that delay in flowering is correlated with a reduction in polyamine accumulation and with a delay in appearance of conjugated polyamines, and we propose that genes carried by the Ri TL-DNA intervene either directly in polyamine metabolism or that polyamine metabolism is closely linked to direct effects of Ri T-DNA expression.