PubMed:17080619 JSONTXT

{"project":"Trait curation","denotations":[{"id":"T1","span":{"begin":358,"end":362},"obj":"1416679"},{"id":"T2","span":{"begin":358,"end":362},"obj":"1659561"},{"id":"T3","span":{"begin":364,"end":369},"obj":"1416682"},{"id":"T4","span":{"begin":808,"end":811},"obj":"174805"},{"id":"T5","span":{"begin":1151,"end":1155},"obj":"1659561"},{"id":"T6","span":{"begin":1151,"end":1155},"obj":"1416679"},{"id":"T7","span":{"begin":1198,"end":1202},"obj":"1659561"},{"id":"T8","span":{"begin":1198,"end":1202},"obj":"1416679"},{"id":"T9","span":{"begin":1332,"end":1336},"obj":"1416679"},{"id":"T10","span":{"begin":1332,"end":1336},"obj":"1659561"}],"text":"Tomato seed germination: regulation of different response modes by phytochrome B2 and phytochrome A.\nLycopersicon 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]."}