Involvement of the auxin\u2013cytokinin homeostasis in adventitious root formation of rose cuttings as affected by their nodal position in the stock plant

Millicent A Otiende,Julius O Nyabundi,Mohammad R Hajirezaei,Klaus Fricke,Kamau Ngamau,Uwe Druege

doi:10.1007/s00425-021-03709-x

Abstract

Main conclusionEnhanced levels of indole-3-acetic and raised auxin to cytokinin ratios in the stem base contribute to the positive acropetal gradient in rooting capacity of leafy single-node stem cuttings of rose.Cuttings excised from different nodal positions in stock plants can differ in subsequent adventitious root formation. We investigated the involvement of the auxin–cytokinin balance in position-affected rooting of Rosa hybrida. Leafy single-node stem cuttings of two rose cultivars were excised from top versus bottom positions. Concentrations of IAA and cytokinins were monitored in the bud region and the stem base during 8 days after planting using chromatography–MS/MS technology. The effects of nodal position and external supply of indole-butyric acid on rooting were analyzed. Most cytokinins increased particularly in the bud region and peaked at day two before the bud break was recorded. IAA increased in both tissues between day one and day eight. Top versus bottom cuttings revealed higher levels of isopentenyladenosine (IPR) in both tissues as well as higher concentrations of IAA and a higher ratio of IAA to cytokinins particularly in the stem base. The dynamic of hormones and correlation analysis indicated that the higher IPR contributed to the enhanced IAA in the bud region which served as auxin source for the auxin homeostasis in the stem base, where IAA determined the auxin–cytokinin balance. Bottom versus top cuttings produced lower numbers and lengths of roots, whereas this deficit was counterbalanced by auxin application. Further considering other studies of rose, it is concluded that cytokinin-, sucrose- and zinc-dependent auxin biosynthesis in the outgrowing buds is an important factor that contributes to the enhanced IAA levels and auxin/cytokinin ratios in the stem base of apical cuttings, promoting root induction.

Highlights

Adventitious root (AR) formation is a fundamental biological process by which new roots are formed post-embryonically from cells of non-root tissues (Steffens and Rasmussen 2016)
We investigated the involvement of the auxin–cytokinin balance in position-affected rooting of Rosa hybrida, regarding potential interferences with plant genotype
The findings, that the acropetal increase of indole3-acetic acid (IAA) levels in the bud region and in the stem base and the resulting higher IAA to CK ratio was consistent between the two cultivars and that independent on cultivar the deficit in AR formation of bottom versus top position cuttings was counterbalanced by external auxin supply, highlights the functional role of auxin in the acropetal stimulation of AR formation and support the conclusion that the found relationships are highly relevant to the frequently observed better rooting of apical cuttings of R. hybrida

Summary

Introduction

Adventitious root (AR) formation is a fundamental biological process by which new roots are formed post-embryonically from cells of non-root tissues (Steffens and Rasmussen 2016). AR formation involves successive developmental phases (da Costa et al 2013; Druege et al 2019). Often the cells first have to acquire root competence involving dedifferentiation. After determination of AR founder cells, new roots are formed by cell division, differentiation and growth. It is widely accepted that auxin, mainly indole3-acetic acid (IAA), is the central player that induces ARs in competent cells. Among the co-players, cytokinins (CKs) are thought to have an early positive regulative function during dedifferentiation, whereas high CK levels act antagonistic to auxin during the induction phase (da Costa et al 2013; Druege et al 2019)

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