Planta 211: 144-149 (2000)

Ethylene promotes ethylene biosynthesis during pea seed germination by positive feedback regulation of 1-aminocyclo-propane-1-carboxylic acid oxidase

Luciana Petruzzelli (1), Immacolata Coraggio (1), Gerhard Leubner-Metzger

Friedrich Miescher Institute, Maulbeerstr. 66, CH-4058 Basel, Switzerland (1) Istituto Biosintesi Vegetali, C.N.R., Via Bassini 15, I-20133 Milano, Italy Received: 28 September 1999 / Accepted: 27 December 1999

Abstract. Increased ethylene evolution accompanies seed germination of many species including Pisum sativum L., but only little is known about the regulation of the ethylene biosynthetic pathway in different seed tissues. Biosynthesis of the direct ethylene precursor 1-aminocyclopropane-1-carboxylic acid (ACC), the expression of ACC oxidase (ACO), and ethylene production were investigated in the cotyledons and embryonic axis of germinating pea seeds. An early onset and sequential induction of ACC biosynthesis, Ps-ACO1 mRNA and ACO activity accumulation and ethylene production were localized almost exclusively in the embryonic axis. Maximal levels of ACC, Ps-ACO1 mRNA, ACO enzyme activity and ethylene evolution were found when radicle emergence was just complete. Treatment of germinating seeds with ethylene alone or in combination with the inhibitor of ethylene action 2,5-norbornadiene showed that endogenous ethylene regulates its own biosynthesis through a positive feedback loop that enhances ACO expression. Accumulation of Ps-ACO1 mRNA and of ACO enzyme activity in the embryonic axis during the late phase of germination required ethylene, whereas Ps-ACS1 mRNA levels and overall ACC contents were not induced by ethylene treatment. Ethylene did not induce ACO in the embryonic axis during the early phase of germination. Ethylene-independent signalling pathways regulate the spatial and temporal pattern of ethylene biosynthesis, whereas the ethylene signalling pathway regulates high-level ACO expression in the embryonic axis, and thereby enhances ethylene evolution during seed germination.  Key words: 1-Aminocyclopropane-1-carboxylic acid oxidase - Ethylene - Feedback regulation - Pisum - Seed germination - Signalling Links to other publications on ethylene and pea seed germination: Petruzzelli et al. 2003 Petruzzelli et al. 1999

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