Expression of Aux/IAA genes during development of sylleptic and proleptic buds in white poplar

In this study, the genes of the Aux/IAA family were used as functional markers to characterise bud break stages in a white poplar clone. In the first experiment, under greenhouse conditions, the sprouting of repressed sylleptic buds was obtained by pruning the shoot tip during growing season. Buds were collected at 0, 6, 24 and 48 h after pruning for molecular analyses. A decrease in transcript level of IAA4 and IAA8 genes was observed in the first and second bud below the cut after 6 and 24 h, respectively. In the second experiment, bud break of post-dormant proleptic buds was induced by forcing in climatic chamber. The first 6 and the following 6 buds below the apical one were sampled every 48 h during forcing. Anatomical studies were also carried out on buds and plants were equipped with stem and bud radial growth sensors to check their swelling. In both experiments, gene expression patterns showed a decrease and a successive increase in expression of IAA4 and IAA8 genes during bud break. The transient down-regulation of these genes was observed only in buds that formed new branches. Thus, similar molecular mechanisms are involved in bud break of both sylleptic and proleptic buds.