Hormone profiling of chrysanthemum hairy roots after co-cultivation with Rhizobium rhizogenes

We have used chrysanthemum as a model crop to determine auxin and cytokinin levels in hairy roots formed after coculture of leaf discs with Rhizobium rhizogenes. All 6 genotypes tested formed hairy roots, upon which the presence of T-DNA genes was tested with a qPCR assay, evaluating the presence of TL- as well as TR-genes. Transformation efficiencies varied between 14 and 100%, and for every cultivar, roots with either only TL-genes and roots with both TL- and TR-genes were found. 2-isopentenyladening (2iP) and indole-3-acetic acid (IAA) levels were compared for all 12 roots that yielded sufficient material for analysis. In two cultivars, multiple TL+TR positive independent root lines could be compared, showing a significant difference for as well auxin as cytokinin levels. However, both for 2iP and IAA, 10-fold differences were detected between roots induced on leaves of a single cultivar. This suggests that phytohormone levels, and probably subsequent hairy root regeneration, depend on individual pRi-gene integration for each separate hairy root.