Planta 235: 137-151 (2012)

Dose- and tissue-specific interaction of monoterpenes with the gibberellin-mediated release of potato tuber bud dormancy, sprout growth and induction of α-amylases and β-amylases

Abstract
Gibberellins (GA) are involved in bud dormancy release in several species. We show here that GA treatment released bud dormancy, initiated bud sprouting and promoted sprout growth of excised potato tuber bud discs ('eyes'). Monoterpenes from peppermint oil (PMO) and S-(+)-carvone (CAR) interact with the GA-mediated bud dormancy release in a hormesis-type response: low monoterpene concentrations enhance dormancy release and the initiation of bud sprouting whereas high concentrations inhibit it. PMO and CAR did however not affect sprout growth rate after its onset. We further show that GA-induced dormancy release is associated with tissue-specific regulation of α- and β-amylases. Molecular phylogenetic analysis shows that potato α-amylases cluster into two distinct groups: α-AMY1 and α-AMY2. GA-treatment induced transcript accumulation of members of both α-amylase groups, as well as α- and β-amylase enzyme activity in sprout and 'sub-eye' tissues. In sprouts, CAR interacts with the GA-mediated accumulation of α-amylase transcripts in an α-AMY2-specific and dose-dependent manner. Low CAR concentrations enhance the accumulation of α-AMY2-type α-amylase transcripts, but do not affect the α-AMY1-type transcripts. Low CAR concentrations also enhance the accumulation of α- and β-amylase enzyme activity in sprouts, but not in 'sub-eye' tissues. In contrast, high CAR concentrations have no appreciable effect in sprouts on the enzyme activities and the α-amylase transcript abundances of either group. The dose-dependent effects on the enzyme activities and the α-AMY2-type α-amylase transcripts in sprouts are specific for CAR but not for PMO. Different monoterpenes therefore may have specific targets for their interaction with hormone signaling pathways.


Key words: alpha-amylase • beta-amylase • bud dormancy release • carvone • gibberellin • hormesis • monoterpenes • peppermint oil • post-harvest sprout inhibitors • potato tuber sprouting • Solanum tuberosum

Financial support: Our work is funded by grants from the Deutsche Forschungsgemeinschaft (Grant DFG LE720/6 and MU3114/1-1) to G.L.-M. and K.M., respectively, and the Wissenschaftliche Gesellschaft Freiburg to A.L., A.V., and Kai Graeber (licenses for Geneious bioinformatics software) which are gratefully acknowledged. We also acknowledge awards related to this work to S.R. by the Faculty of Biology in Freiburg, and to M.I. in the national competition ‘Schweizer Jugend forscht’ in Switzerland. Further information: 'The Seed Biology Place' - www.seedbiology.de.