Auxins or Sugars: What Makes the Difference in the Adventitious Rooting of Stored Carnation Cuttings?
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Cold storage of cuttings is frequently applied in the vegetative propagation of ornamental plants. Dianthus caryophyllus was used to study the limiting influences of auxin and sugars on adventitious root formation (ARF) in cuttings stored at 5°C. Carbohydrate levels during storage were modulated by exposing cuttings to low light or darkness. The resulting cuttings were treated (or not) with auxin and planted, and then ARF was evaluated. Carbohydrate levels in the cuttings were monitored and the influence of light treatment on indole-3-acetic acid (IAA) and zeatin (Z) in the basal stem was investigated. Dark storage for up to 4 weeks increased the percentage of early rooted cuttings and the final number and length of adventitious roots, despite decreased sugar levels in the stem base. Light during cold storage greatly enhanced sugar levels, particularly in the stem base where the Z/IAA ratio was higher and ARF was lower than observed in the corresponding dark-stored cuttings. Sugar levels in nonstored and dark-stored cuttings increased during the rooting period, and auxin application enhanced the accumulation of sugars in the stem base of nonstored cuttings. Auxin stimulated ARF most strongly in nonstored, less so in light-stored, and only marginally in dark-stored cuttings. A model of auxin-sugar interactions in ARF in carnation is proposed: cold storage brings forward root induction and sink establishment, both of which are promoted by the accumulation of auxin but not of sugars, whereas high levels of sugars and probably also of cytokinins act as inhibitors. Subsequent root differentiation and growth depend on current photosynthesis.
KeywordsRoot development Light Dark exposure Temperature Carbohydrates Source-sink Plant hormones Signaling
The work was supported by the Ministry of Science and Innovation of Spain (projects MICINN/FEDER AGL-2008-02472 and AGL-2004-07902); the Federal Ministry of Food, Agriculture and Consumer Protection of Germany; the State Ministry of Rural Development, Environment and Consumer Protection of Brandenburg; and the Ministry for Agriculture, Nature and Environment Protection of the Free State of Thüringen. M. A. Agulló thanks the Spanish MICINN for a FPI fellowship and a travel grant. We appreciate the skillful technical assistance of Baerbel Broszies and Sabine Czekalla (IGZ, Erfurt) and the valuable help of Dr. A. Torrecillas (CAID, Universidad de Murcia) with hormonal analyses. The authors are grateful to Drs. G. Garrido and E. Cano (Barberet & Blanc S.A., Murcia, Spain) for the plant material supplies.
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