A novel rejuvenation approach to induce endohormones and improve rhizogenesis in mature tree.

BACKGROUND

is a difficult-to-root tree. In the present study, we successfully rejuvenated stock plants by grafting and then burying them horizontally.

RESULTS

Rooting rates of rejuvenated shoots were 98.1% 20 days after cutting. We recorded spatial and temporal variation in endogenous indole-3-acetic acid (IAA), abscisic acid (ABA), gibberellin A (GA) and zeatin-riboside (ZR) under root induction. The four types of endohormones were mainly confined to the phloem sieve and companion cells (S&Cs) at the base of either rejuvenated or mature soft shoots. IAA and ABA levels were higher in rejuvenated shoots than in mature shoots, whereas the opposite was true for GA and ZR. During rooting induction, GA was the first hormone to be observed outside phloem S&Cs, followed by IAA, ABA and ZR. In rejuvenating soft shoots, IAA accumulated in the cross-sectional areas of the cambium and phloem, where root primordia were evident.

CONCLUSIONS

The improvement in the rooting ability that was evident after rejuvenation most likely results a transformation of the plant to a juvenile form, from elevated IAA levels in phloem S&Cs and from a promotion of all four endohormones outside phloem S&Cs, in particular, from an accumulation of IAA in the cross-sectional areas of the cambium and phloem.