Tomato seed germination: regulation of different response modes by phytochrome B2 and phytochrome A

Authors

  • KLAUS-J. APPENROTH,

    Corresponding author
    1. University of Jena, Institute of General Botany and Plant Physiology, Dornburger Str. 159, 07743 Jena, Germany and
      Klaus-J. Appenroth. Fax: +49 3641 949232; e-mail: Klaus.Appenroth@uni-jena.de
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  • GABRIELE LENK,

    1. University of Jena, Institute of General Botany and Plant Physiology, Dornburger Str. 159, 07743 Jena, Germany and
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    • *

      Ms Gabriele Lenk died on 7 May 2004.

  • LYDIA GOLDAU,

    1. University of Jena, Institute of General Botany and Plant Physiology, Dornburger Str. 159, 07743 Jena, Germany and
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  • RAMESHWAR SHARMA

    1. University of Hyderabad, School of Life Sciences, Hyderabad, India
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Klaus-J. Appenroth. Fax: +49 3641 949232; e-mail: Klaus.Appenroth@uni-jena.de

ABSTRACT

Lycopersicon esculentum seeds germinate after rehydration in complete darkness. This response was inhibited by a far-red light (FR) pulse, and the inhibition was reversed by a red light (R) pulse. Comparison of germination in phytochrome-deficient mutants (phyA, phyB1, phyB2, phyAB1, phyB1B2 and phyAB1B2) showed that phytochrome B2 (PhyB2) mediates both responses. The germination was inhibited by strong continuous R (38 µmol m−2 s−1), whereas weak R (28 nmol m−2 s−1) stimulated seed germination. Hourly applied R pulses of the same photon fluence partially replaced the effect of strong continuous R. This response was called ‘antagonistic’ because it counteracts the low fluence response (LFR) induced by a single R pulse. This antagonistic response might be an adaptation to a situation where the seeds sit on the soil surface in full sunlight (adverse for germination), while weak R might reflect that situation under a layer of soil. Unexpectedly, the effects of continuous R or repeated R pulses were mediated by phytochrome A (PhyA). We therefore suggest that low levels of PhyA in its FR-absorbing form (Pfr) cause inhibition of seed germination produced either by extended R irradiation (by degradation of PhyA-Pfr) or by extended FR irradiation [keeping a low Pfr/R-absorbing form (Pr) ratio].

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