Abstract :
[en] The shoot apical meristem (SAM) of Sinapis alba can be switched from vegetative to reproductive fate by exposure of 2-month old plants to a single long day (LD). Floral transition then occurs in good synchrony within a population, and a number of biochemical, cellular, and morphological changes have been described. Our aim is to integrate gene expression patterns into this timing. We report here the analysis of SaLFY, orthologous to the floral meristem identity gene LEAFY of Arabidopsis. Materials and Methods: Plants of Sinapis were grown in 8-h shorts days for two months before being induced to flower by one 22-h LD. Shoot apices were harvested 24, 32, 40, 48, 56 and 80h after start of the LD, and prepared for in situ hybridization (Melzer et al., 1999). Results and Conclusions: As expected, the expression of SaLFY was very strong in flower primordia. More surprisingly, SaLFY was expressed well before the initiation of flowers. First, a strong signal was detected in the tip of young leaf primordia of vegetative plants. Secondly, SaLFY was transiently expressed in the SAM of induced plants, from 32h after the start of the LD, when cell proliferation increased. The signal formed, in transverse sections, a discontinuous ring with activation where last leaves were to be initiated. Interestingly, this activation in the SAM matched in time and space early growth changes previously described during the transition to flowering, namely an increase of leaf primordia growth and an acceleration of last leaf initiation (Bernier, 1997), suggesting that SaLFY may have dual functions in fate specification during the floral transition of the SAM. References: Bernier G 1997. J Exp Bot 48; 1071-1077. Melzer S, Kampmann G, Chandler J, Apel K 1999. Plant J 18; 395-405.
