Cell-specific photosynthetic gene expression in maize determined using cell separation techniques and hybridization in situ.

Bundle sheath strands and mesophyll cell extracts have been isolated from maize (Zea mays L.) leaves using a mechanical disruption-filtration technique. Northern blot analysis showed that phosphoenolpyruvate carboxylase (PEPCase; EC 4.1.1.31) mRNA accumulates only in mesophyll cells. The mechanisms regulating the cell-specific expression of this gene must, therefore, be at either the level of RNA transcription or that of mRNA turnover. The first successful application of hybridization to mRNA molecules in photosynthetic plant tissue sections is described. Results obtained from this in situ study corroborate our finding that PEPCase mRNA accumulates only in mesophyll cells as well as the previously reported (Link, G, DM Coen, L Bogorad 1978 Cell 15: 725-731) finding that the accumulation of ribulose 1,5-bisphosphate carboxylase (RuBPCase; EC 4.1.1.39) large subunit mRNA is restricted to bundle sheath cells. Demonstrating the differential accumulation of PEPCase mRNA and RuBPCase mRNA by utilizing the in situ hybridization technique paves the way for its use as a powerful tool in relating cellular differentiation to gene expression during plant development.