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Tomato seed germination: regulation of different response modes by phytochrome B2 and phytochrome A
Author(s) -
APPENROTH KLAUSJ.,
LENK GABRIELE,
GOLDAU LYDIA,
SHARMA RAMESHWAR
Publication year - 2006
Publication title -
plant, cell and environment
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.646
H-Index - 200
eISSN - 1365-3040
pISSN - 0140-7791
DOI - 10.1111/j.1365-3040.2005.01455.x
Subject(s) - phytochrome , germination , phytochrome a , darkness , mutant , lycopersicon , biology , biophysics , botany , far red , fluence , irradiation , horticulture , red light , arabidopsis , biochemistry , physics , gene , nuclear physics
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 µ mol 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].