IN SITU LOCALIZATION OF SPECIFIC mRNAs IN PLANT TISSUES
In situ hybridization permits the localization of specific mRNA transcripts at the cellular level by hybridizing a specific probe to tissue sections in which the mRNA is preserved. Thus. in situ hybridization is a powerful method for studying gene expression during development. In addition to specific cellular localization. it offers the advantage over other methods. such as northern analysis, of increased sensitivity: mRNAs of low abundance can be detected even in a few cells. Moreover, genes that are expressed only at certain developmental stages and/ or in specific cell types can be studied. For example, we have used in situ hybridization techniques successfully to study the spatial patterns of expression of nodulin genes in Rhi:ohium meliloti-induced alfalfa root nodules (Figure lA-D).