Spatial patterns of gene expression in Brassica napus seedlings: identification of a cortex-specific gene and localization of mRNAs encoding isocitrate lyase and a polypeptide homologous to proteinases.

We investigated the spatial expression of three genes that are expressed during seed germination and postgerminative development in Brassica napus L. using in situ hybridization procedures. Two of the mRNAs encode isocitrate lyase and a predicted polypeptide that is homologous to cysteine proteinases. We reported previously that the mRNAs are prevalent primarily in cotyledons of seedlings and accumulate with similar kinetics during postgerminative growth. Here, we show that the two mRNAs are detected in several seedling tissues, but they display different distribution patterns in both cotyledons and root-shoot axes. The third mRNA is abundant in seedling axes and accumulates specifically in the ground meristem and mature cortex of hypocotyls and roots. Distribution of the mRNA in root meristems suggests that the gene product participates in an early event in cortical cell differentiation. Our results provide insight into the physiological processes that characterize seedlings.