title: Tomato seed germination: regulation of different response modes by phytochrome B2 and phytochrome A.
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 micromol 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].
authors.affiliation: University of Jena, Institute of General Botany and Plant Physiology, Dornburger Str. 159, 07743 Jena, Germany. Klaus.Appenroth@uni-jena.de
authors.forename: Klaus J
authors.initials: KJ
authors.lastname: Appenroth
authors.forename: Gabriele
authors.initials: G
authors.lastname: Lenk
authors.forename: Lydia
authors.initials: L
authors.lastname: Goldau
authors.forename: Rameshwar
authors.initials: R
authors.lastname: Sharma
mesh_terms: D018525:Germination / Q000235:genetics / Q000502:physiology* / Q000528:radiation effects; D008027:Light; D018551:Solanum lycopersicum / Q000235:genetics / Q000254:growth & development* / Q000378:metabolism; D009154:Mutation; D051942:Phytochrome A / Q000235:genetics / Q000502:physiology*; D051939:Phytochrome B / Q000235:genetics / Q000502:physiology*; D010940:Plant Proteins / Q000235:genetics / Q000502:physiology*; D012639:Seeds / Q000235:genetics / Q000254:growth & development* / Q000378:metabolism
chemical_list: D051942:Phytochrome A; D010940:Plant Proteins; D051939:Phytochrome B