Abstract
The rooting of stem cuttings is a highly efficient procedure for the vegetative propagation of ornamental plants. In cultivated carnations, an increased auxin level in the stem cutting base produced by active auxin transport from the leaves triggers adventitious root (AR) formation from the cambium. To provide additional insight into the physiological and genetic basis of this complex trait, we studied AR formation in a collection of 159 F1 lines derived from a cross between two hybrid cultivars (2003 R 8 and 2101-02 MFR) showing contrasting rooting performances. In three different experiments, time-series for several stem and root architectural traits were quantified in detail in a subset of these double-cross hybrid lines displaying extreme rooting phenotypes and their parental genotypes. Our results indicate that the water content and area of the AR system directly contributed to the shoot water content and shoot growth. Moreover, morphometric data and rooting quality parameters were found to be associated with some stress-related metabolites such as 1-aminocyclopropane-1-carboxylic acid (ACC), the ethylene precursor, and the conjugated auxin indol-3-acetic acid-aspartic acid (IAA-Asp).
Highlights
In contrast to most root tissues, adventitious roots (ARs) arise from non-root cells in response to some abiotic stresses or after wounding [1,2]
Despite the high auxin biosynthesis and transport rate in 2003 R 8, the high expression of GRETCHEN HAGEN3 (GH3) genes in the stem cutting base of this cultivar enhanced the conjugation of the active auxin indol-3-acetic acid (IAA) to amino acids, such as aspartic acid, which directly contributed to quick turnover of active auxin in the cambium [7]
We found a significant variation in the stem cutting size, estimated by the SA_13 trait, between sowings in both parental lines (Figure 1a and Supplementary Materials Figure S1)
Summary
In contrast to most root tissues, adventitious roots (ARs) arise from non-root cells in response to some abiotic stresses or after wounding [1,2]. Carnation (Dianthus caryophyllus L.) plants are vegetatively propagated from terminal stem cuttings that undergo adventitious rooting, a process which has a strong genetic dependency and which leads to production losses in certain commercial cultivars [4]. Plants 2019, 8, 226 or a slow elongation rate of these ARs. In addition, genome-wide gene expression profiling and functional changes occurring in the stem cutting base during the early stages of adventitious rooting were further analyzed in two of these cultivars, 2003 R 8 and 2101-02 MFR, which were selected because of their contrasting rooting performances [6]. Differences in rooting ability were caused by delayed activation of formative divisions from cambial-derived cells in the bad rooting cultivar (2003 R 8), a phenotype that could be rescued by exogenous auxin treatment [6]. Despite the high auxin biosynthesis and transport rate in 2003 R 8, the high expression of GRETCHEN HAGEN3 (GH3) genes in the stem cutting base of this cultivar enhanced the conjugation of the active auxin indol-3-acetic acid (IAA) to amino acids, such as aspartic acid, which directly contributed to quick turnover of active auxin in the cambium [7]
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