AOBPreview published online on October 21, 2008
Annals of Botany, doi:10.1093/aob/mcn203
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Exogenous ethylene inhibits sprout growth in onion bulbs
Institut für Sonderkulturen und Produktionsphysiologie (370), Universität Hohenheim, Emil-Wolffstr. 25, 70593 Stuttgart, Germany
* For correspondence. E-mail buflergw{at}uni-hohenheim.de
Received: 10 June 2008 Returned for revision: 2 September 2008 Accepted: 12 September 2008
Background and Aims: Exogenous ethylene has recently gained commercial interest as a sprouting inhibitor of onion bulbs. The role of ethylene in dormancy and sprouting of onions, however, is not known.
Methods: A cultivar (Allium cepa ‘Copra’) with a true period of dormancy was used. Dormant and sprouting states of onion bulbs were treated with supposedly saturating doses of ethylene or with the ethylene-action inhibitor 1-methylcyclopropene (1-MCP). Initial sprouting was determined during storage at 18 °C by monitoring leaf blade elongation in a specific size class of leaf sheaths. Changes in ATP content and sucrose synthase activity in the sprout leaves, indicators of the sprouting state, were determined. CO2 and ethylene production of onion bulbs during storage were recorded.
Key results: Exogenous ethylene suppressed sprout growth of both dormant and already sprouting onion bulbs by inhibiting leaf blade elongation. In contrast to this growth-inhibiting effect, ethylene stimulated CO2 production by the bulbs about 2-fold. The duration of dormancy was not significantly affected by exogenous ethylene. However, treatment of dormant bulbs with 1-MCP caused premature sprouting.
Conclusions: Exogenous ethylene proved to be a powerful inhibitor of sprout growth in onion bulbs. The dormancy breaking effect of 1-MCP indicates a regulatory role of endogenous ethylene in onion bulb dormancy.
Key words: Bulb dormancy, Allium cepa, onion, sprout growth, ethylene, CO2 production, respiration, 1-methylcyclopropene