Germination and storage reserve mobilization are regulated independently in Arabidopsis

Authors

  • Sarah L. Pritchard,

    1. Centre for Novel Agricultural Products, Department of Biology, University of York, Heslington, York YO10 5YW, UK,
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  • Wayne L. Charlton,

    1. Centre for Plant Sciences, Leeds Institute of Biotechnology and Agriculture, University of Leeds, Leeds LS2 9JT, UK
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  • Alison Baker,

    1. Centre for Plant Sciences, Leeds Institute of Biotechnology and Agriculture, University of Leeds, Leeds LS2 9JT, UK
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  • Ian A. Graham

    Corresponding author
    1. Centre for Novel Agricultural Products, Department of Biology, University of York, Heslington, York YO10 5YW, UK,
      * For correspondence (fax +44 1904 328762; e-mail iag1@york.ac.uk).
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* For correspondence (fax +44 1904 328762; e-mail iag1@york.ac.uk).

Summary

The phytohormone abscisic acid (ABA) inhibits the germination of many seeds, including Arabidopsis, but the mechanism for this is not known. In cereals, ABA inhibits the expression of genes involved in storage reserve mobilization. We have found that in Arabidopsis ABA decreases transcription from the promoters of marker genes for β-oxidation and the glyoxylate cycle, essential pathways for the conversion of storage lipid (triacylglycerol) into sucrose. Thirty per cent of stored lipid is broken down over 6 days following imbibition of ABA-treated seed. Sucrose levels in ABA-treated seeds, rather than decreasing as under normal growth conditions, actually double during the 3 days following imbibition. This sucrose is derived from triacylglycerol as demonstrated by two mutants disrupted in the conversion of triacylglycerol into sucrose, kat2 and icl1, which do not accumulate sucrose in the presence of ABA. We conclude that the ABA block on germination is not a consequence of inhibition of storage lipid mobilization. Two independent programmes appear to operate, one that is blocked by ABA, governing developmental growth resulting in germination; and a second that governs storage lipid mobilization which is largely ABA-independent.

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