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

Dong Pei,Junpei Zhang,Xiaobo Song,Hao Liu,Qingguo Ma,Ying Gao

doi:10.1186/s13007-018-0280-0

Dong Pei, Junpei Zhang + Show 4 more

Open Access

https://doi.org/10.1186/s13007-018-0280-0

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Abstract

BackgroundJuglans is a difficult-to-root tree. In the present study, we successfully rejuvenated stock plants by grafting and then burying them horizontally.ResultsRooting 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 A3 (GA3) 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 GA3 and ZR. During rooting induction, GA3 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.ConclusionsThe 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.

Highlights

Some studies have shown that rejuvenation of mature trees or the induction of plants to regress from maturity to the juvenile state may significantly improve adventitious root formation (ARF)
Adventitious roots broke through the epidermis after 10 days of induction (Fig. 1c, c1)
Adventitious rooting occurred from the basal regions of rejuvenated soft shoots and was longitudinally distributed along the stem (Fig. 1d, d1)

Summary

Introduction

We successfully rejuvenated stock plants by grafting and burying them horizontally. When trees age, their capacity to form adventitious roots becomes weaker and propagation via cuttings becomes increasingly difficult. From growers’ point of view, it is important to improve the adventitious root formation (ARF) capacities of mature trees. Some studies have shown that rejuvenation of mature trees or the induction of plants to regress from maturity to the juvenile state may significantly improve ARF. Rejuvenation restores the juvenile features of trees, for example, by increasing the activities of esterases and peroxidases [21], and by improving photosynthetic and respiratory rates [22]. Huang et al [24] found that rooting abilities of successive generations of Buxussinica

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