AOBPreview originally published online on March 8, 2007
Annals of Botany 2007 99(4):735-745; doi:10.1093/aob/mcm008
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Ethylene Production is Associated with Germination but not Seed Dormancy in Red Rice
1 CRA-Experimental Institute for Cereal Research, Section of Fiorenzuola, s.s. via S. Protaso 302, 29017 Fiorenzuola d'Arda (PC), Italy
2 Life Science Trace Gas Exchange Facility, Molecular and Laser Physics, Radboud University, Toernooiveld, 6525 ED Nijmegen, The Netherlands
3 Istituto Biosintesi Vegetali, CNR, Via Bassini 15, 20133 Milano, Italy
* For correspondence. E-mail agianinetti{at}tin.it
Received: 20 October 2006 Returned for revision: 15 November 2006 Accepted: 20 December 2006 Published electronically: 8 March 2007
Background and Aims: The relationship between ethylene production and both seed dormancy and germination was investigated using red rice (weedy rice) as a model species.
Methods: Both fully dormant and after-ripened (non-dormant) naked caryopses were incubated with or without inhibitors of ethylene synthesis [aminoethoxyvinylglycine (AVG)] and perception [silver thiosulfate (STS)], or in the presence of the natural ethylene precursor 1-aminocyclopropane-1-carboxylic acid (ACC). The kinetics of ethylene emissions were measured with a sensitive laser–photoacoustic system.
Key Results: Dormant red rice caryopses did not produce ethylene. In non-dormant caryopses, ethylene evolution never preceded the first visible stage of germination (pericarp splitting), and ethylene inhibitors completely blocked ethylene production, but not pericarp splitting. Accordingly, endogenous ACC appeared to be lacking before pericarp splitting. However, early seedling growth (radicle or coleoptile attaining the length of 1 mm) followed ethylene evolution and was delayed by the inhibitors. Wounding the dormant caryopses induced them to germinate and produce ethylene, but their germination was slow and pericarp splitting could be speeded up by ethylene.
Conclusions: The findings suggest that, in red rice, endogenous ethylene stimulates the growth of the nascent seedling, but does not affect seed dormancy or germination inception. Correspondingly, this phytohormone does not play a role in the dormancy breakage induced by wounding, but accelerates germination after such breakage has occurred.
Key words: Seed dormancy, red rice, Oryza sativa f. spontanea, ethylene inhibitors, wounding
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